CSWI P 3.2 – Senior Welding I nspect or
WI S10
Training and Exam inat ion Ser vices
Grant a Park , Gr eat Abingt on
Cam bridge CB21 6AL
Unit ed Kingdom
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CSWIP 3.2 Senior Welding Inspector
CSWIP 3.2 Senior Welding Inspection
Introduction
WIS10
Copyright © TWI Ltd
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The Course
 The Senior Welding Inspector course covers a
variety of subjects that somebody operating at
this level will have to have a comprehensive
knowledge of.
 Once each subjected is presented it will be
reinforced with 10 questions relating to that
subject. As the examination is multi choice
these questions will also be.
Course Subjects
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QA and QC
Destructive testing
Heat treatments
Welding procedures
Welding dissimilar
Residual stress and
distortion
 Weldability
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Weld fractures
Welding symbols
Non destructive testing
Welding consumables
Weld repairs
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Specifications
Joint design
HSLA steels
Arc energy and heat
input
There will also be homework each night in multi choice
format which will be reviewed the following day.
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Course Assessment
Exam after the
course is completed
No continuous
assessment
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CSWIP Certificate Scheme
 3.0 Visual Welding Inspector
 3.1 Welding Inspector
 3.2 Senior Welding Inspector
 For further examination information please see
website www.cswip.com
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0‐1
CSWIP 3.2 Examination
 The TWI Specification
will be used.
 To attempt the
Senior Welding
Inspectors
Examination (3.2)
you must already be
a holder of the
Welding Inspectors
Qualification (3.1).
CSWIP 3.0 Examination
Before attempting the examination, you MUST
provide the following
 Two passport size photographs, with your name
and signature on reverse side of both.
 Eye test certificate, the certificate must show near
vision and colour tests. (N4.5 or Times Roman
numerals standard) and verified enrolment.
 Completed examination form, you can print from
the website www.twi.training.com
It is the sole responsibility of the candidate to provide the
above. Failure to do so will delay results and certification
being issued.
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CSWIP 3.2 Examination
 3.2.1
Without radiograph interpretation
70% pass mark required in all areas
of examination
 3.2.2
With radiograph interpretation
(Optional)
70% Pass mark required in all areas
of examination including radiographic
interpretation before certificate can be
issued.
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CSWIP 3.2 Examination
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CSWIP 3.2 Examination
There are four sections to the examination each will
require 70% pass mark for the qualification to be awarded.
 Part 1 General Multi-choice 30 Questions
45 minutes
 Part 2 Scenario multi choice 60 questions
150 minutes
 Part 3 Assessment of four NDT Reports 40 Questions
75 minutes
 Part 4 The interpretation of weld symbols using a
drawing 10 questions
30 minutes
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CSWIP 3.2 Examination
All of the questions from all of the sections are
generated individually from a large data base so no
one student has the same exam.
For candidates wishing to complete the RT supplementary
examination
In the case of the scenario section of 60 questions,
12 topics will be randomly generated, each with 4
questions from the 12 sections presented through
the week and 12 questions directly related to the
specification.
 Theory: Density and Sensitivity Calculations 1 hour
The exam specification, will be required for most of
the scenario and NDT questions but not for the
General and weld symbol questions.
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 Theory B2: Radiographic general theory 20 multiplechoice questions 30 Minutes
 Practical D2: Interpretation of Radiographs
 Metal Group A: Ferrous 6 Radiographs 1 Hour 30
Minutes
 Metal Group B: Austenitic 3 Radiographs 45 Minutes
 Metal Group C: Aluminum 3 Radiographs 45 minutes
 Metal Group D: Copper 3 Radiographs 45 minutes
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0‐2
Notification of Examination Results
70% Pass mark
required for
EVERY section
of the exam
CSWIP 3.2 Renewals
5 years
10 years
Log book submittal
Renewal examination
2 copies of certificates and an identity card
sent to delegates’ sponsor
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Certification Scheme for
Personnel
Recognised Worldwide
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0‐3
CSW I P 3 .2 – Se n ior W e ldin g I n spe ct or
Con t e n t s
Se ct ion
Subj e ct
1
D u t ie s of t h e Se n ior W e ldin g I nspe ct or
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.11
1.12
Leader ship skills
Technical skills
Knowledge of t echnology
Knowledge of norm at ive docum ent s
Knowledge of planning
Knowledge of organisat ion
Knowledge of qualit y/ audit ing
Man m anagem ent
Recruit m ent
Morals and m ot ivat ion
Discipline
Sum m ary
2
W e lde d Join t D e sign
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
Welds
Types of j oint
Fillet welds
But t welds
Dilut ion
Welding sym bols
Welding posit ions
Weld j oint preparat ions
Designing welded j oint s
Sum m ary
3
Qu a lit y Assu r an ce a n d Qu a lit y Con t r ol
3.1
3.2
3.3
3.4
3.5
3.6
Definit ions
Qualit y syst em st andards
Audit ing and docum ent at ion
Qualit y requirem ent s for w elding
Calibrat ion/ validat ion of welding equipm ent
Workshop exercise
4
Code s a n d St an da r ds
4.1
4.2
4.3
4.4
Com pany m anuals
Audit ing
Codes and st andards
Sum m ary
5
Fe - C St e e ls
5.1
St eel t erm inology
6
D e st r u ct ive Te st in g
6.1
6.2
6.3
Test t ypes, t est pieces and t est obj ect ives
Fract ur e t est s
Macr oscopic exam inat ion
WI S10- 30816
Cont ent s
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7
H e a t Tr e a t m en t
7.1
7.2
7.3
7.4
7.5
Heat t r eat m ent of st eel
Post weld heat t r eat m ent ( PWHT)
PWHT t herm al cycle
Heat t r eat m ent furnaces
Local PWHT
8
W PS a n d W e lde r Qu a lifica t ion s
8.1
8.2
Qualified welding procedure specificat ions
Welder qualificat ion
9
Ar c En er gy a n d H e at I n pu t
9.1
9.2
Curr ent and v olt age
Arc energy or heat im put
10
Re sidu a l St r ess a n d D ist or t ion
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
What causes dist ort ion?
What ar e t he m ain t ypes of dist ort ion?
What ar e t he fact or s affect ing dist ort ion?
Dist ort ion – prevent ion by pr e- set t ing, pre- bending or use of r est raint
Dist ort ion – prevent ion by design
Elim inat ion of w elding
Dist ort ion – prevent ion by fabricat ion t echniques
Dist ort ion – corr ect ive t echniques
11
W e lda bilit y of St e e ls
11.1
11.2
11.3
11.4
Fact or s t hat effect w eldabilit y
Hydr ogen cracking
Solidificat ion cracking
Lam ellar t earing
12
W e ld Fr a ct ur es
12.1
12.2
12.3
Duct ile fract ur es
Brit t le fract ure
Fat igue fract ure
13
W e ldin g Sym bols
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
13.9
13.10
13.11
13.12
St andards for sym bolic represent at ion of welded j oint s on drawings
Elem ent ary w elding sym bols
Com binat ion of elem ent ary sym bols
Supplem ent ary sym bols
Posit ion of sym bols on drawings
Relat ionship bet ween t he arr ow line and t he j oint line
Posit ion of t he refer ence line and posit ion of t he w eld sym bol
Posit ions of t he cont inuous line and t he dashed line
Dim ensioning of welds
I ndicat gion of t he w elding process
Ot her inform at ion in t he t ail of t he r eference line
Weld sym bols in accordance wit h AWS 2.4
14
NDT
14.1
14.2
14.3
14.4
Radiographic m et hods
Magnet ic part icle t est ing
Dye penet rant t est ing
Surface cracks det ect ion ( m agnet ic part icle/ dye penet rant ) : general
WI S10- 30816
Cont ent s
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15
Welding Consumables
15.1
15.2
15.3
15.4
15.5
15.6
15.7
15.8
MMA electrodes
Cellulosic electrodes
Rutile electrodes
Basic electrodes
Classification of electrodes
TIG filler wires
MIG/MAG filler wires
SAW filler wires
16
MAG welding
16.1
16.2
16.3
16.4
The process
Process variables
Welding consumables
Important inspection point/checks when MIG/MAG welding
17
MMA Welding
17.1
17.2
17.3
17.4
17.5
17.6
17.7
17.8
Manual metal arc/shielded metal arc welding (MMA/SMAW)
MMA welding basic equipment requirements
Power requirements
Welding variables
Voltage
Type of current and polarity
Type of consumable electrode
Typical welding defects
18
Submerged Arc Welding
18.1
18.2
18.3
The process
Process variables
Storage and care of consumables
19
TIG Welding
19.1
19.2
19.3
19.4
19.5
19.6
19.7
19.8
Process characteristics
Process variables
Filler wires and shielding gases
Tungsten inclusions
Crater cracking
Common applications of the TIG process
Advantages of the TIG process
Disadvantages of the TIG process
20
Weld Repairs
20.1
20.2
Production repairs
In-service repairs
Appendix
Appendix
Appendix
Appendix
WIS10-30816
Contents
1
2
3
4
Homeworks
NDT Training Reports
Training Drawing
Specification Questions
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Se ct ion 1
D u t ie s of t h e Se n ior W e ldin g I n spe ct or
1
D u t ie s of t h e Se n ior W e ldin g I nspe ct or
The Senior Welding I nspect or has prim arily a supervisor y/ m anagerial role,
which could encom pass t he m anagem ent and cont r ol of an inspect ion cont ract .
The role w ould cert ainly include leading a t eam of Welding I nspect or s, who will
look t o t he Senior Welding I nspect or for guidance, especially on t echnical
subj ect s. The Senior Welding I nspect or will be expect ed t o give advice, r esolve
problem s, t ak e decisions and generally lead from t he fr ont , som et im es in
difficult sit uat ions.
The at t ribut es required by t he Senior Welding I nspect or are varied and t he
em phasis on cert ain at t ribut es and skills m ay differ fr om proj ect t o proj ect .
Essent ially t hough t he Senior Welding I nspect or will require leadership skills,
t echnical skills and experience.
1 .1
Le a de r ship sk ills
Som e aspect s on t he t heory of leadership m ay be t aught in t he classroom , but
leadership is an inherent part of t he char act er and t em peram ent of an
individual. Pract ical applicat ion and experience play a m aj or part in t he
dev elopm ent of leadership skills and t he Senior Welding I nspect or should st rive
t o im prov e and fine t une t hese skills at every opport unit y.
The skills required for t he developm ent of leader ship include a:
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1 .2
Willingness and abilit y t o accept inst ruct ions or orders from senior st aff and
t o act in t he m anner pr escribed.
Willingness and abilit y t o give orders in a clear and concise m anner,
whet her v erbal or writ t en, which will leave t he recipient in no doubt as t o
what act ion or act ions are r equired.
Willingness t o t ak e r esponsibilit y, part icularly when t hings go w rong,
perhaps due t o t he Senior Welding I nspect or ’s direct ion, or lack of it .
Capacit y t o list en ( t he basis for good com m unicat ion skills) if and when
explanat ions are necessar y and t o provide const ruct ive r easoning and
advice.
Willingness t o delegat e r esponsibilit y t o allow st aff t o get on wit h t he j ob
and t o t rust t hem t o act in a professional m anner. The Senior Welding
I nspect or should, wherever possible, st ay in t he background, m anaging.
Willingness and abilit y t o support m em bers of t he t eam on t echnical and
adm inist rat ive issues.
Te chnica l sk ills
A num ber of fact or s m ake up t he t echnical skills r equired by t he Senior Welding
I nspect or and t hese are a knowledge of:
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Technology.
Nor m at ive docum ent s.
Planning.
Organisat ion.
Audit ing.
WI S10- 30816
Dut ies of t he Senior Welding I nspect or
1- 1
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1 .3
Know le dge of t e ch nology
Welding t echnology knowledge r equired by t he Senior Welding I nspect or is v ery
sim ilar t o t hat required by t he Welding I nspect or, but wit h som e addit ional
scope and dept h.
Cert ain areas wher e addit ional knowledge is required are a:
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1 .4
Knowledge of qualit y assurance and qualit y cont rol.
Sound appreciat ion of t he four com m only used non- dest ruct ive t est ing
m et hods.
Basic underst anding of st eel m et allurgy for com m only welded m at erials and
t he applicat ion of t his underst anding t o t he assessm ent of fract ure sur faces.
Assessm ent of non- dest ruct ive t est report s, par t icularly t he int erpr et at ion of
radiographs.
Know le dge of nor m a t ive docu m e nt s
I t is not a requirem ent for I nspect ors at any lev el t o m em orise t he cont ent of
relevant norm at ive docum ent s, except possibly wit h t he except ion of t aking
exam inat ions.
Specified norm at ive docum ent s ( specificat ions, st andards, codes of pract ice,
et c) should be available at t he workplace and t he Senior Welding I nspect or
would be expect ed t o read, under st and and apply t he requirem ent s wit h t he
necessary level of precision and direct ion required.
The Senior Welding I nspect or should be aware of t he m ore widely used
st andards as applied in welding and fabricat ion. For exam ple:
1 .5
BS EN I SO 15614 / ASME I X
St andards for welding procedur e approval
BS 4872, BS EN 287/ BS EN I SO
9606 / ASME I X
PED BS 5500 / ASME VI I I
St andards for welder approval.
BS EN I SO 9000 – 2000
St andards for qualit y m anagem ent .
St andards for qualit y of fabricat ion.
Know le dge of pla n nin g
Any proj ect or cont ract will require som e planning if inspect ion is t o be carried
out effect ively and wit hin budget .
See Sect ion: Planning for m ore det ailed inform at ion.
1 .6
Know le dge of or ga nisa t ion
The Senior Welding I nspect or m ust hav e good organisat ional skills in order t o
ensur e t hat t he inspect ion requirem ent s of any qualit y/ inspect ion plan can be
m et , wit hin t he allocat ed t im e, budget and using t he m ost suit able per sonnel
for t he act ivit y. Assessm ent of suit able personnel m ay require considerat ion of
t heir t echnical, physical and m ent al abilit ies in order t o ensur e t hat t hey are
able t o perfor m t he t asks required of t hem . Ot her considerat ions would include
availabilit y of inspect ion personnel at t he t im e required, levels of supervision
and t he m onit oring of t he inspect or’s act ivit ies form st art t o cont ract
com plet ion.
WI S10- 30816
Dut ies of t he Senior Welding I nspect or
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1 .7
Know le dge of qu a lit y / a u dit ing
Ther e ar e m any sit uat ions in m anufact uring or on a pr oj ect wher e t he Senior
Welding I nspect or m ay be r equired t o carr y out audit s.
See sect ion on: Qualit y Assurance/ Qualit y Cont rol and I nspect ion for m or e
det ailed inform at ion.
1 .8
M a n m a na ge m e nt
As m ent ioned abov e, t he Senior Welding I nspect or will have t o
wit h a t eam of I nspect ion personnel which he m ay well have
have t o liaise wit h cust om er r epr esent at ives, sub- cont ract ors
I nspect or s. He m ay have t o invest igat e non- com pliances, deal
discipline as well as per sonal m at t ers of his st aff.
direct and work
t o pick. He will
and t hird part y
wit h m at t ers of
To do t his effect ively he needs skills in m an m anagem ent .
1 .9
Re cr u it m e nt
When r ecruit ing an individual or a t eam t he SWI will first have t o est ablish t he
requirem ent s of t he wor k. Am ong t hem w ould be:
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What skills are definit ely required for t he wor k and what addit ional ones
would be desirable?
Are part icular qualificat ions needed?
I s experience of sim ilar wor k desirable?
What physical at t ribut es ar e needed?
I s t he work local, in- shop, on- sit e, in a t hird world count ry?
Does t he j ob require w orking unsociable hours being away from hom e for
long periods?
I s t he j ob for perm anent st aff or for a fixed t er m ?
I f overseas what ar e t he leave and t ravel ar rangem ent s?
What is t he likely salary?
During subsequent int erviews t he SWI will need t o assess ot her aspect s of t he
candidat es’ suit abilit y:
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1 .1 0
Has he t he abilit y t o work on his own init iat ive?
Can he w or k as part of a t eam ?
I f overseas has t he person been t o a sim ilar locat ion?
What is his m arit al/ hom e sit uat ion?
Are t her e any Passport / Visa problem s likely?
M or a le a nd m ot iv a t ion
The m orale of a workfor ce has a significant effect on it s perform ance so t he
SWI m ust st rive t o keep t he personnel happy and m ot ivat ed and be able t o
det ect signs of low m or ale.
Low m orale can lead t o am ong ot her t hings, poor productivity, less good
workm anship, lack of diligence, taking short cut s, ignoring safet y pr ocedures and
higher levels of absent eeism .
The SWI needs t o be able t o recognise t hese signs and ot hers such as
per sonnel not st art ing wor k pr om pt ly, t aking longer breaks, t alking in groups
and grum bling about m inor m at t er s.
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Dut ies of t he Senior Welding I nspect or
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A good supervisor should not allow his wor kforce t o get int o such a st at e.
He m ust k eep t hem m ot ivat ed by:
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1 .1 1
His own dem eanour – does he have drive and ent husiasm or is he seen t o
have no energy and generally depressed. The w ork force will r eact
accordingly.
I s he seen t o be leading fr om t he fr ont in a fair and consist ent m anner?
Favourit ism in t he t reat m ent of st aff, on disciplinary m at t ers, t he allocat ion
of w ork, allot m ent of overt im e, week end w or king and holidays are com m on
causes of problem s.
Keep t hem inform ed in all aspect s of t he j ob and t heir sit uat ion. Rum ours of
im pending redundancies or cut s in allowances et c will not m ake for good
m orale.
D isciplin e
Any workfor ce m ust be working in a disciplined m anner, norm ally t o rules and
st andards laid down in t he Com pany’s condit ions of em ploym ent or relevant
com pany handbook. The SWI m ust hav e a good underst anding of t hese
requirem ent s and be able t o apply t hem in a fair and equit able m anner.
He m ust hav e a clear underst anding as t o t he lim it s of his aut horit y – knowing
how far he can go in disciplinary proceedings.
The usual st ages of disciplinary pr ocedur e ar e:
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The quiet word.
Form al verbal warning.
Writ t en warning.
Possible dem ot ion, t ransfer, suspension.
Dism issal wit h not ice.
I nst ant dism issal.
Usually aft er t he writ t en warning st age t he m at t er will be handled by t he
Com pany’s Per sonnel or Hum an Resources Depart m ent .
I t is of vit al im port ance t hat t he com pany rules are rigorously followed as any
deviat ion could result in claim s for unfair or const ruct ive dism issal.
I n dealing wit h disciplinary m at t er s t he SWI m ust :
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Act pr om pt ly.
Mean what he says.
Tr eat every one fairly and as an adult .
Avoid const ant com plaining on pet t y issues.
Wher e t her e ar e serious breaches of com pany rules by one or t w o people t he
rest of t he w orkfor ce should be inform ed of t he m at t er so t hat rum our and
count er- rum ours can be quashed.
Som e m at t er s of discipline m ay well arise because of incor rect wor king
pract ices, passing off below qualit y work, signing for work which has not been
done, et c.
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Dut ies of t he Senior Welding I nspect or
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I n all such cases t he SWI will need t o carry out an invest igat ion and apply
disciplinary sanct ions t o t he personnel involved.
To do t his:
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1 .1 2
First est ablish t he fact s – by int erviewing st aff, from t he relevant r ecords,
by having recheck s on part of t he j ob.
I f any suspicions are confirm ed, t ransfer/ r em ov e suspect per sonnel from
t he j ob pending disciplinary proceedings. I f t he per sonnel ar e em ployed by a
sub- cont ract or t hen a m eet ing wit h t he sub- cont ract or will be needed t o
achieve t he sam e end.
Find out t he ext ent of t he pr oblem , is it localised or widespr ead?
I s t here need t o inform t he cust om er and t hird part y inspect or?
Form ulat e a plan of act ion, wit h ot her com pany depart m ent s wher e
necessary , t o r et riev e t he sit uat ion.
Carr y out t he necessary disciplinary m easur es on t he personnel involved.
Convene a m eet ing wit h t he r est of t he w ork for ce t o infor m t hem of t he
sit uat ion and ensure t hat any sim ilar lapses will be dealt wit h sever ely.
Follow up t he m eet ing wit h a writ t en m em o.
Sum m a r y
The Senior Welding I nspect or’s r ole can be varied and com plex, a num ber of
skills need t o be dev eloped in order for t he individual t o be effect ive in t he role.
Ev er y Senior Welding I nspect or will have personal skills and at t ribut es which
can be br ought t o t he j ob, som e of t he skills ident ified abov e m ay already have
been m ast er ed or under st ood. The im port ant t hing for t he individual t o
recognise is not only do t hey hav e unique abilit ies which t hey can bring t o t he
role, but t hey also need t o st rive t o be t he best t hey can by st rengt hening
ident ifiable weak ar eas in t heir knowledge and underst anding.
Som e way s in which t hese goals m ay be achieved is t hrough:
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Em bracing fact s and r ealit ies.
Being creat ive.
Being int erest ed in solving problem s.
Being pro- act ive not r eact ive.
Having em pat hy wit h ot her people.
Having personal values.
Being obj ect ive.
WI S10- 30816
Dut ies of t he Senior Welding I nspect or
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Se ct ion 2
W e lde d Join t D e sign
2
W e lde d Join t D e sign
This sect ion is principally concerned wit h st ruct ures fabricat ed by w elding st eel
plat es t oget her, exam ples include bridges, ships, offshore plat form s, pressur e
vessels and pipelines, alt hough in som e cases t his m ay involve welding curv ed
plat es t oget her.
This sect ion int roduces t ypical j oint geom et ries involved in j oining plat es
t oget her and describes t he t ypes of weld used in t hese j oint configurat ions wit h
t ypical feat ures of but t and fillet welds described. For t he st ruct ure t o funct ion
loads m ust be t ransferr ed from one plat e t o anot her and t he feat ur es of welds
t hat enable t hem t o t ransm it loads are described. Finally, som e exam ples of
good and bad design pract ice ar e given.
2 .1
W e lds
A weld is a perm anent union bet ween m at erials caused by t he applicat ion of
heat , pr essur e or bot h and if m ade bet w een t wo faces approxim at ely parallel is
known as a but t weld.
Figur e 2 .1 But t w e ld.
A weld m ade bet w een t wo faces t hat ar e approxim at ely at right angles t o each
ot her is known as a fillet weld.
Figur e 2 .2 Fille t w e ld.
For sim plicit y t hese diagram s show an arc welding process t hat deposit s filler
weld m et al in a single weld pass. Typical feat ures of a but t weld are shown in
Figure 2.3 and t hose of a fillet weld in Figure 2.4.
The weld or w eld m et al refer s t o all t he m at erial t hat has m elt ed and resolidified. The heat - affect ed zone ( HAZ) is m at erial t hat has not m elt ed but
whose m icrost ruct ur e has been changed as a r esult of t he welding. The fusion
line is t he int erface bet ween t he w eld m et al and t he HAZ.
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The r oot is t he bot t om of t he weld or nar row est part and t he face is t he t op or
widest part . At t he corner s of t he w eld cr oss sect ion wher e t he weld m et al j oins
t he par ent m et al ar e t he w eld t oes. These are at each corner of bot h t he weld
face and w eld root in a but t weld but only on t he w eld face in a fillet weld.
a
Fusion line
Weld m et al
Weld t oe
HAZ
Parent
m et al
b
Figur e 2 .3 Typica l fe a t ur e s of a :
a
b
But t w e ld.
D ou ble - side d bu t t w e ld.
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Figur e 2 .4 Typica l fe a t ur e s of a fille t w e ld.
The applicat ion of heat nat urally causes som e changes t o t he m icrost ruct ur e
parent m at erial, t he HAZ shown in Figure 2.5 for a but t w eld in st eel wit h
sim ilar HAZs dev eloped in t he par ent m at erial of fillet welds. Close t o t he fusion
line t he t em perat ure in t he HAZ has been sufficient t o cause m icrost ruct ural
phase changes, which will result in recry st allisat ion and grain growt h. Furt her
away fr om t he fusion line t he parent m at erial has been heat ed t o a lower
m axim um t em perat ur e and t he par ent m icrost r uct ure is t em pered.
Solid- liquid boundary
Maxim um
t em perat ure
Solid
weld
m et al
Grain growt h zone
Recryst allised zone
Part ially t ransform ed zone
Tem pered zone
Unaffect ed base m at erial
Figur e 2 .5 H AZs in a but t w e ld.
The dist ance bet w een weld t oes is t he weld widt h. When t he dist ance is
bet ween t he t oes at t he weld cap it is t he weld cap widt h, t he dist ance bet ween
t he t oes at t he root is t he w eld root widt h.
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The height of t he addit ional weld m et al in t he weld cap is t he excess weld m et al
which used t o be called reinfor cem ent which wrongly suggest s t hat incr easing
t his dim ension will st rengt hen t he weld. I f t he excess weld m et al is t oo great it
increases t he st r ess concent rat ion at t he weld t oe and t his ext ra weld m et al is
called t he excess r oot penet rat ion.
Weld widt h
Excess
weld m et al
Excess root
penet rat ion
Figur e 2 .6 D e finit ions on a but t w e ld.
2 .2
Type s of j oint
A j oint can sim ply be described as a configurat ion of m em bers and can be
described independent ly of how it is welded. Figures 2.7 and 2.8 show t he m ost
com m on j oint t ypes - but t and T j oint . Ot her t ypical j oint t ypes are shown in
Figures 2.9- 2.11; lap, cruciform and corner j oint . When designing a lap j oint t he
ov erlap bet ween t he t wo plat es needs t o be at least four t im es t he plat e
t hickness ( D = 4t ) , but not less t han 25m m .
Figur e 2 .7 But t j oint .
Figur e 2 .8 T j oint .
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Figur e 2 .9 La p j oint s.
Figur e 2 .1 0 Cr ucifor m Joint
Figur e 2 .1 1 Cor ne r j oint .
An alt ernat ive t o a convent ional lap j oint is t o weld t he j oint using plug or slot
welding, shown in Figure 2.12 showing t he t ypical lap j oint can be drast ically
alt ered. The hole for a slot weld should have a widt h at least t hree t im es t he
plat e t hickness and not less t han 25m m . I n plat e less t han 10m m t hickness, a
hole of equal widt h t o t he plat e t hickness can be w elded as a plug weld.
a
b
Figur e 2 .1 2 :
a
b
Slot w e lde d la p j oint .
Plug w e lde d la p j oint .
Corner j oint s can be fit t ed and w elded in a num ber of ways. The unwelded
pieces can be assem bled eit her wit h an open corner or closed t oget her. The
weld can be on t he ext ernal or int ernal corner or bot h in a double- sided weld.
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Open
Closed
Ext ernal corner j oint
I nt ernal corner j oint
Double- sided corner j oint
Figur e 2 .1 3 D iffe r e nt t ype s of cor ne r j oint s, un w e lde d a nd w e lde d.
2 .3
Fille t w e lds
The t hroat and leg lengt h of a fillet weld are shown in Figure 2.14. Throat size a
is generally used as t he design param et er since t his part of t he w eld bear s t he
st resses and can be r elat ed t o leg lengt h z by t he following relat ionship: a ≈
0.7z and z ≈ 1.4a.
Throat a
Leg
Leg z
Figur e 2 .1 4 Le g le ngt h z a nd t hr oa t siz e a in a fille t w e ld.
This is only valid for m it re fillet welds having sim ilar leg lengt hs ( Figure 2.15) ,
so is not valid for concave, conv ex or asym m et ric welds. I n concave fillet welds
t he t hroat t hickness will be m uch less t han 0.7 t im es t he lengt h. The leg lengt h
of a fillet weld is oft en approxim at ely equal t o t he m at erial t hickness. The act ual
t hroat size is t he widt h bet ween t he fused w eld root and t he segm ent linking
t he t wo weld t oes, show n as t he red line in Figure 2.16. Due t o root penet rat ion
t he act ual t hroat size of a fillet weld is oft en larger t han it s design size but
because of t he unpr edict abilit y of t he root penet rat ion ar ea, t he de sign t hr oat
size m ust a lw a y s be t aken as t he st r ess par am et ers in design calculat ions.
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z
a
z
Figur e 2 .1 5 M it r e fille t w e ld.
Figur e 2 .1 6 D e sign t hr oa t of a fille t w e ld.
Convex fillet weld
Concave fillet weld
Mit re fillet weld
Figur e 2 .1 7 Fille t w e ld cr oss- se ct ions.
Act ual
t hroat
Design t hroat
Design t hroat =
act ual t hroat
Figur e 2 .1 8 D e finit ion of de sign a n d a ct ua l t hr oa t in conca ve a n d con ve x fille t
w e lds.
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The choice bet ween m it re weld, concav e and conv ex fillet weld needs t o
account for t he weld t oe blend. A concav e fillet weld gives a sm oot h blend
profile and a low st ress concent r at ion at t he fillet weld t oe. Convex fillet welds
can have a higher st ress concent rat ion at t he weld t oe. I f t he fluidit y of t he
weld pool is not cont rolled it is possible t o obt ain an asym m et rical fillet weld
wher e t he weld pool has sagged int o t he j oint preparat ion and t here is also a
risk of undercut on t he bot t om w eld t oe ( see Figure 2.19) . Having a sm oot h t oe
blend is im port ant t o give bet t er fat igue perfor m ance for fillet welds.
Figur e 2 .1 9 Fille t w e ld t oe ble nds.
2 .4
But t w e lds
The design t hroat t 1 of a but t weld is t he penet rat ion dept h below t he par ent
plat e surface and no account is m ade of t he excess weld m et al. The design
t hroat is t her efor e less t han t he act ual t hroat t 2 .
Figur e 2 .2 0 D e sign t hr oa t t 1 a nd t he a ct ua l t hr oa t t 2 for but t w e lds.
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The weld t oe blend is im port ant for but t welds as well as fillet welds. Most codes
st at e t hat weld t oes shall blend sm oot hly, leaving it open t o individual
int erpr et at ion. The higher t he t oe blend angle t he gr eat er t he am ount of st r ess
concent rat ion. The t oe blend angle ideally should be bet ween 20- 30 degr ees
( Figure 2.21) .
6mm
Poor weld t oe blend angle
3mm
I m proved weld t oe blend angle
Figur e 2 .2 1 Toe ble n d in but t w e lds.
2 .5
D ilut ion
When filler and parent m at erial do not have t he sam e com posit ion t he result ing
com posit ion of t he weld depends largely on t he weld preparat ion before
welding. The degr ee of dilut ion result s fr om t he edge pr eparat ion and process
used; t he percent age of dilut ion ( D) is part icularly im port ant when welding
dissim ilar m at erials and is expr essed as t he rat io bet ween t he w eight of parent
m at erial m elt ed and t he t ot al weight of fused m at erial ( m ult iplied by 100 t o be
expr essed as a percent age) , as shown:
D=
Weight of parent material melted
× 100
Total weight of fused material
Low dilut ions are obt ained wit h fillet welds and wit h but t welds wit h m ult iple
runs. For a single pass bet t er dilut ion is obt ained wit h grooved welds, see
Figure 2.22.
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Fille t w e lds
Single V gr oove w e ld
Squa r e gr oove w e ld
Figur e 2 .2 2 Effe ct of w e ld pr e pa r a t ion on dilut ion a nd w e ld m e t a l com posit ion
( for a single pa ss only) .
2 .6
W e lding sy m bols
On engineering drawings a welded j oint can be represent ed by differ ent m eans.
A det ailed represent at ion shows ev ery det ail and dim ension of t he j oint
preparat ion wit h carefully writ t en, ext ensive not es. I t pr ovides all t he det ails
required t o produce a part icular weld in a very clear m anner but requires a
separat e det ailed sk et ch ( t im e consum ing and can ov erburden t he drawing) .
For a special weld preparat ion not covered in t he r elevant st andards ( eg nar row
groov e welding) ; it is t he only way t o indicat e t he way com ponent s are t o be
prepared for w elding or brazing.
8-12°
8- 12
1-3
≈R6
R6
8mm
1-4
Figur e 2 .2 3 D e t a ile d r e pr e se nt a t ion of U be ve l angle .
Sym bolic represent at ion using weld sym bols can specify j oining and inspect ion
inform at ion and t he UK has t r adit ionally used BS 499 Part 2 which has been
superseded by BS EN ISO 2553. I n m any w elding and fabricat ion organisat ions
use old draw ings t hat reference out of dat e st andards such as BS 499 Pt 2.
BS EN ISO 2553 is alm ost ident ical t o t he original BS EN I SO 2553
st andard on which it was based. I n Am erica AWS A2.4 is followed, while
sym bols for brazing are given in EN 14324.
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The advant ages of sym bolic represent at ion ar e:




Sim ple and quick t o visualise on t he drawing.
Does not overburden t he drawing.
No need for addit ional views as all welding sym bols can be placed on t he
m ain assem bly drawing.
Gives all necessary indicat ions regarding t he specific j oint t o be obt ained.
Sym bolic represent at ion can only be used for com m on j oint s and requires
t raining t o underst and t he sym bols. Sym bolic represent at ion of a welded j oint
cont ains an arr ow line, a r efer ence line and an elem ent ary sy m bol. The
elem ent ary sym bol can be com plem ent ed by a supplem ent ary sy m bol. The
arr ow line can be at any angle ( ex cept 180 degrees) and can point up or down.
The arr ow head m ust t ouch t he surfaces of t he com ponent s t o be j oined and
t he locat ion of t he weld. Any int ended edge preparat ion or w eldm ent is not
shown as an act ual cross- sect ional represent at ion but as a line. The arr ow also
point s t o t he com ponent t o be pr epar ed wit h single prepar ed com ponent s.
Figur e 2 .2 4 Sym bolic r e pr e se nt a t ion of U be ve l a ngle .
BS EN I SO 2553 and AWS A2.4 list all t he m ain elem ent ary sym bols, som e
exam ples are shown in Table 2.1. The sym bols for arc welding are oft en shown
as cross- sect ional represent at ions of a j oint design or com plet ed weld.
Sim ple, single edge preparat ions are shown in Figure 2.25.
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Ta ble 2 .1 Ele m e nt a r y w e ld sym bols.
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Ke y:
a =
b =
c =
d =
e =
f
=
single V but t j oint .
double V but t j oint .
single bevel but t j oint .
double bevel but t j oint .
single sided fillet weld.
double sided fillet weld.
Figur e 2 .2 5 W e lding sym bols for t he m ost com m on j oint t ype s sh ow n on a
r e fe r e nce line .
These sim ple sym bols can be int erpret ed as eit her t he j oint det ails alone or t he
com plet ed w eld. For a finished weld it is norm al for an appropriat e weld shape
t o be specified. Ther e are a num ber of opt ions and m et hods t o specify an
appropriat e weld shape or finish. But t welded configurat ions would norm ally be
shown as a convex profile ( Figure 2.26 a, d and f) or as a dressed- off weld as
shown in b and c. Fillet weld sym bols are always shown as a m it re fillet weld
and a convex or concav e profile can be superim posed ov er t he original sym bol's
m it re shape.
Ke y:
a
b
c
d
e
f
=
=
=
=
=
=
single V but t weld wit h conv ex profile.
double V but t weld flushed off bot h sides on weld face.
single bev el but t weld flushed off bot h sides on weld face.
double bev el but t convex ( as w elded) .
concav e fillet weld.
double sided convex fillet weld.
Figur e 2 .2 6 W e lding sy m bols show ing t he w e ld pr ofile for t he m ost com m on
j oint t ype s.
So t he cor r ect size of w eld can be applied it is com m on t o find num bers t o t he
left or right of t he sy m bol. For fillet welds num bers t o t he left indicat e t he
design t hroat t hickness, leg lengt h or bot h ( Figure 2.27) .
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a7 z 10
a7 z 10
Figur e 2 .2 7 Thr oa t a n d le g le ngt h dim e n sion s give n on t he w e ld sy m bol for a
fille t w e ld.
For but t j oint s and welds an S wit h a num ber t o t he left of a sym bol refer s t o
t he dept h of penet rat ion. When t here ar e no specific dim ensional requirem ent s
specified for but t welds on a drawing using weld sym bols, it would norm ally be
assum ed t hat t he requirem ent is for a full penet rat ion but t weld. Num ber s t o
t he right of a sym bol or sym bols relat e t o t he longit udinal dim ension of welds,
eg for fillet s t he num ber of welds, weld lengt h and weld spacing for noncont inuous welds.
Figur e 2 .2 8 W e ld sym bols sh ow in g t he w e ld le ngt h dim e nsions t o t h e r ight of
t he w e ld j oint sym bols f or a n int e r m it t e nt fille t w e ld.
Supplem ent ary sym bols can be used for special cases wher e addit ional
inform at ion is required ( Figure 2.29) . The w eld all round sym bols m ay be used
for a r ect angular hollow sect ion ( RHS) welded t o a plat e, for exam ple. The flag
sym bol for w eld in t he field or on sit e can be added t o any st andard sym bol. A
box at t ached t o t he t ail of t he ar r ow can cont ain or point t o ot her inform at ion
such as whet her NDT is required. This inform at ion is som et im es t he welding
process t ype given as a t hree num ber reference from BS EN I SO 4063, for
exam ple 135 refers t o MAG welding.
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Figur e 2 .2 9 Ex a m ple s of supple m e nt a r y sym bols.
2 .7
W e lding posit ion s
I n weld procedur e docum ent s and engineering drawings t he t ype and
orient at ion of welds ar e oft en given a t w o let t er abbreviat ion which defines
t hem w hich can vary depending on t he st andard t he w elds are conform ing t o.
The abbreviat ions here are consist ent wit h BS EN I SO 6947 and are
sum m arised in Table 2.2.
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Ta ble 2 .2 W e lding posit ions.
Welding posit ion
Figure/ sym bol
Abbreviat ion
Flat
PA
Horizont al
PB
Horizont al vert ical
PC
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Welding posit ion
2 .8
Figure/ sym bol
Abbreviat ion
Vert ical up,
vert ical down
PG/ PF
Ov erhead
PE
Horizont al
ov erhead
PD
W e ld j oint pr e p a r a t ions
The sim plest w eld j oint preparat ion is a squar e edged but t j oint , eit her closed or
open. A closed but t j oint is used in t hick plat e for k eyhole welding processes
such as laser or elect r on beam welding ( EBW) . A square edged open but t j oint
is used for t hinner plat e up t o 3m m t hickness for arc w elding in a single pass or
in t hick plat e for w elding processes such as elect roslag welding.
Square edge
closed but t
Square edge
open but t
Figur e 2 .3 0 Squa r e e dge but t j oint s.
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I t is norm al t o use a bev el on t he edges of t he par ent m et al t o be w elded t o
allow access t o t he root for t he first welding pass which is filled using fill passes.
Single- sided preparat ions ar e norm ally m ade on t hinner m at erials or when
access fr om bot h sides is rest rict ed. Double- sided preparat ions ar e norm ally
m ade on t hicker m at erials or when access fr om bot h sides is unr est rict ed.
Edge pr eparat ion design includes t he bevel angle ( or included angle if bot h
sides are bevelled) and also t he square edges r oot face and root gap. I n a j oint
wher e bot h sides are bev elled t he pr eparat ion is t erm ed a V or v ee pr eparat ion
( Figure 2.31) . V prepar at ions are usually used for plat e of 3- 20m m t hickness.
An alt ernat ive is a U pr eparat ion ( or J preparat ion if only one side has t he edge
preparat ion) where t he edge is m achined int o t he shape of a U. This is used in
t hicker plat e, over 20m m t hickness, wher e it uses less filler m et al t han a V
preparat ion j oint . J or U edge pr eparat ions also require a bev el angle and root
face, t he gap t o be defined, a root radius and land t o be specified ( Figure 2.32) .
Single- sided edge preparat ions are oft en used for t hinner m at erials or when
t here is no access t o t he root of t he w eld ( pipelines) . I f t her e is access t o bot h
sides of t he m at erial t hen a double- sided edge preparat ion is used, especially
for t hicker m at erials. Single and double edge preparat ions are shown in Figure
2.33.
Included angle
Bevel angle
Root face
Gap
Figur e 2 .3 1 Sin gle V be ve l.
Included angle
Root radius
Bevel
angle
Root
face
Gap
Land
Figur e 2 .3 2 U be ve l.
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Single Bevel
Single J
Single V
Single U
Double Bevel
Double V
Double J
Double U
Figur e 2 .3 3 Ra nge of single a nd double - side d be ve l, V, J a nd U pr e pa r a t ions.
2 .9
D e sign ing w e ld e d j oint s
Weld j oint design select ion will also be influenced by pract ical issues such as t he
welding process used and t he access r equired t o obt ain root fusion. The bevel
angle m ust allow good access t o t he r oot and sufficient m anipulat ion of t he
elect r ode t o ensure good sidewall fusion ( Figure 2.34) . I f t he included angle is
t oo large t hen heavy dist ort ions can result and m ore filler m et al is required. I f
t he included angle is t oo sm all t here is a risk of lack of penet rat ion or lack of
sidewall fusion. Typical bev el angles are 30- 35 degr ees in a V preparat ion ( 6070 degrees included angle) . I n a single bevel j oint t he bevel angle m ight be
increased t o 45 degrees.
Figur e 2 .3 4 Be ve l a ngle t o a llow e le ct r ode m a nipula t ion for side w a ll fusion.
The root gap and face are select ed t o ensure good r oot fusion ( Figure 2.35) .
This will depend on t he welding process and heat input . I f t he r oot gap is t oo
wide or r oot face t oo narr ow t here is a risk of burn t hrough. I f t he root gap is
t oo nar row or root face is t oo deep t her e is a risk of lack of root penet rat ion. A
balance m ust be found and designed for; t his differ ence in weld root size is
shown in Figure 2.36. High heat input processes r equire a larger r oot face but
less weld m et al which reduces dist ort ions and increases product ivit y. Typical
values for t he r oot face are 1.5- 2.5m m and t he root gap 2- 4m m .
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Figur e 2 .3 5 The im por t a nce of se le ct ing t he cor r e ct r oot fa ce a nd ga p.
a
b
Figur e 2 .3 6 Root siz e for w e lding pr oce sse s w it h diffe r e nt he a t input s:
a
b
Low he a t input .
H igh he a t input .
I f t he com ponent s are t o be j oined by an arc w elding process t he select ed
bev els need t o be adequat ely m achined t o allow t he w elding t ool t o access t he
root of t he w eld. This considerat ion would not apply for a procedure such as
EBW as shown in Figure 2.37. I f using gas- shielded processes t hen t he size of
t he gas nozzle m ay lim it t he abilit y t o use a J pr eparat ion for t hick sect ion
m at erial as it would be difficult t o ensure good root fusion if t he welding head
could not access t he bot t om of t he weld groov e and a single bevel m ay be
needed inst ead ( Figure 2.38) .
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a
b
Figur e 2 .3 7 Pr e pa r a t ion diffe r e nce s be t w e e n:
a
b
Ar c.
Ele ct r on be a m w e ldin g.
a
b
Figur e 2 .3 8 Usin g ga s- shie lde d a r c w e lding:
a
b
D iff icult ie s of r oot a cce ss in a J p r e p a r a t ion.
I m pr ove d de sign usin g a be ve l pr e pa r a t ion .
Choosing bet ween a J or U preparat ion and a bevel or V preparat ion is also
det erm ined by t he cost s or pr oducing t he edge pr eparat ion. Machining a J or U
preparat ion can be slow and expensive. Using t his j oint design also r esult s in
t ight er t olerance which can be easier t o set - up. A bevel or V preparat ion can be
flam e or plasm a cut fast and cheaply r esult ing in larger t olerances, m eaning
t hat set - up can be m or e difficult .
Backing bar or st rip is used t o ensure consist ent root fusion and avoid burn
t hrough. Perm anent backing bar ( rat her t han one rem ov ed aft er w elding) , gives
a built - in crevice which can m ake t he j oint s suscept ible t o corr osion ( Figure
2.39) . When using back ing for alum inium welds any chem ical cleaning reagent s
m ust be rem ov ed befor e assem bling t he j oint . A backing bar also gives a lower
fat igue life.
Figur e 2 .3 9 Usin g a ba ck ing ba r for a but t w e ld.
Separat e fr om t he design of t he j oint and weld access t o w eld locat ions and t he
order in which welds are m ade are im port ant . Figure 2.40 shows exam ples of
t he lim it at ions of access in designing welded j oint s and gives im proved designs.
I t is im port ant t o ensur e t hat it is indeed possible t o m ak e w elds as r equired by
t he drawing.
WI S10- 30816
Welded Joint Design
2- 21
Copyright © TWI Lt d
Figur e 2 .4 0 Ex a m ple s of im pr ove d w e ld de signs w he r e t he r e is lim it e d a cce ss.
2 .1 0
Sum m a r y
You should now:


Be able t o label t he part s of a but t and fillet weld and of a V and U edge
preparat ions.
Recognise welding sym bols and know what t hey m ean.
WI S10- 30816
Welded Joint Design
2- 22
Copyright © TWI Lt d
Outline
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Welded Joint Design
Section 2
What determines joint Design?
Weld features.
Types of welded joints.
Welding symbols.
Weld positions.
Weld bevels.
Designing welded joints.
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Copyright © TWI Ltd
Types of Welds
Weld
A permanent union between materials caused by
heat, and or pressure (BS499).
Fillet Welds
Fillet welds
Throat
Butt weld
Fillet weld
Leg
Leg size
Leg
Throat size
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Butt Joint Preparations
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Single Sided Butt Preparations
Single sided preparations are normally made on thinner
materials, or when access from both sides is restricted
Square Edge
Closed Butt
Single bevel
Single V
Single-J
Single-U
Square Edge
Open Butt
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2‐1
Double Sided Butt Preparations
Double sided preparations are normally made on thicker materials, or
when access form both sides is unrestricted
Joint Preparation Terminology
Angle of bevel
Root
Radius
Double -Vee
Double -Bevel
Root Face
Root Gap
Double - U
Double - J
Single bevel butt
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Joint Preparation Terminology
Included angle
Included angle
Angle of
bevel
Root
radius
Root face
Root gap
Single-V butt
Angle of bevel
Root Gap
Root Face
Land
Single-J butt
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What determines welded joint design?
Design, fatigue life expectancy, loading types
Full penetration butt weld gives better life
expectancy compared to partial penetration and
compound weld gives better performance than a
fillet weld.
Root face
Root gap
Single-U butt
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What determines welded joint design?
Welding process
 Open root runs with SAW. (Difficult unless
backing is used or closed)
 Closed square edge butt joints key hole
Plasma and Electron Beam. (Key hole
technique used)
 Thin wall S/S Dairy pipe closed square edge
butt joint TIG.
 Access for large welding heads U butts.
 Positional welding with SAW.
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What determines welded joint design?
Material thickness
 Butt welds, generally, as material gets thicker
single preparations become double
preparations. (Dependent on access)
 Butt welds, generally as material gets thinner,
root gaps close.
 T joints, generally as material gets thicker, the
vertical plate is prepared. (Compound weld)
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2‐2
What determines welded joint design?
Quality
Root penetration is guaranteed if backing is
used, ceramic or a material that won’t fuse,
shaped to produce a particular profile.
What determines welded joint design?
Quality
To ensure that root defects are minimised, back
gouge and check via NDT, MPI/Dye pen.
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Access and Weld preparations
Access impacts upon weld preparation
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What determines welded joint design?
Welding position
Preparation for
horizontal welding
using the submerged
Arc welding process
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What determines welded joint design?
Welding position
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What determines welded joint design?
Weld volume
 A U butt between 20-30% less weld volume
than a V Butt.
 The benefits could be reduced costs, reduced
residual stress and reduced distortion.
 The disadvantages of the U is the additional
preparation costs of machining although fit up
conditions improve.
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2‐3
What determines welded joint design?
Weld volume
What determines welded joint design?
Distortion control
Double V butt
 A double V has less weld volume than a single V.
 A double V, therefore will reduce cost, reduce
distortion and stress and should guarantee
higher quality.
 Disadvantage of the double V, access to both
sides required.
 The asymmetrical V butt, ⅓,
Distortion control
Shrinkage
ଶ
ଷ
is often used to
control distortion. The smaller v is completed
first.
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What determines welded joint design?
Asymmetrical V butt
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What determines welded joint design?
Level of penetration
Shrinkage
Full penetration
Partial penetration
The U butt has significantly less liquid metal and a more
even distribution of weld metal in the upper most regions
than the V butt. Therefore, greater shrinkage and
distortion occurs with the V butt.
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What determines welded joint design?
Level of penetration
Small root face
Full penetration
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What determines welded joint design?
Gas purging of pipes
Large root face
Less penetration
It is much easier to regulate the gas purge if the
joint is closed.
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2‐4
Nozzles
Set-On Nozzle
 Shorter nozzle is cheaper.
 Easy to make groove for full or
partial penetration.
 Single side welding in 2G/PB
position means high welder skill
is required.
 Through thickness stress means
danger of lamellar tearing.
 Can be difficult to UT especially
on smaller diameters.
 Mainly used for small (<2inch
diameter) nozzles, or thick wall
or large diameter vessels.
 May require reinforcement.
 Extra cost to shape nozzle to
radius of shell.
Nozzles connect a pressure
vessel with other components
Type of nozzle depends on
 Diameter/thickness ratio of the shell.
 Diameter/thickness ratio of the nozzle.
 Access (one side only or both sides).
 Type of joint required (partial/full pen).
 Groove preparation methods available.
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Set-On Nozzle
Set-Through Nozzle
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1G/PA position much easier.
Groove prep can be flame cut.
No danger of lamellar tearing.
Easy access to the back side of
root, so full penetration is easier
to achieve.
For nozzles with small diameters
no need for reinforcement.
Nozzle body needs to be longer.
Greater weld volume means
higher distortions.
Can be hard to UT on smaller
diameters, usually easy to inspect.
Used for larger diameter nozzles,
and thinner walled small diameter
vessels.
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Reinforcement or Compensation
To compensate for loss in strength, we can
reinforce either the shell or nozzle
Reinforcing ring/
Compensating plate
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What determines welded joint design?
Less known joint designs
Welded insert, consumable socket
ring (CSR) or EB insert, used on small
bore pipework where consistent root
penetration is required.
Long neck
nozzle
Sweepolet, shaped to fit radius of
shell, butt welded to shell with a butt
joint on the vertical stem.
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Copyright © TWI Ltd
2‐5
Narrow Gap Joint
Narrow Gap Welding Head
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Joint Design
As a Senior Welding Inspector you are assigned
to the fabrication of a C/Mn pressure vessel.
The vessels main barrel thickness and dished
ends are 25mm wall thickness, all nozzles (set in
and set on), man ways 20mm thickness.
During the fabrication and welding your main
concerns are distortion control, joint design, and
all other quality aspects.
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Question 2
You notice that the joint preparations are not
shown on the Engineering drawing or the WPS.
In the case of a set on nozzle attachment which
of the following joint preparations would be the
most suited?
a.
b.
c.
d.
Open corner joint
Fillet joint
Single bevel butt joint
Single V butt joint
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Question 1
You notice that the joint preparations are not
shown on the Engineering drawing for a set in
nozzle attachment. Which of the following
preparations would be suitable when a full
penetration weld was required?
a.
b.
c.
d.
Single bevel butt joint
Fillet joint
Lap joint
Corner weld
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Questions 3
The fabricator suggests to you that it would be much more
cost effective to weld up the pressure vessel from the out
side only without any back gouging. The WPS shows all the
main barrel sections and dished end to barrel joints are full
penetration butt welds, welded by the SAW welding process,
back gouged root from the inside, welded with the MMA
process. Would you agree with his suggestions?
a. Yes, SAW welding can be used from one side providing
the root gap is greater than 3mm
b. Yes, SAW welding can be used from one side and would
provide a much stronger joint when compared to a back
gouged joint
c. No, SAW welding would never be considered on any
material <50mm thickness
d. No, the SAW welding process can’t be used on a open
root joint welded from one side only
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2‐6
Question 4
When considering distortion, which of the
following butt weld preparations would be the
most suited for the longitudinal welded main
barrel joints?
a.
b.
c.
d.
Double U but weld
Single V butt weld
Single U butt weld
All options would produce the same amount
of distortion
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Question 6
Which distortion control technique is referenced
in the TWI specification?
a.
b.
c.
d.
Raised heat input technique
Back welds
Back skip welding
Full penetration welds
Question 5
The fabricator proposes to you that he wishes to
reduce the bevel angle from 45° to 30° on the
set on nozzle joints. Which of the following
issues may occur if this was permitted?
a. The reduction in bevel angle may result in an
increase in distortion
b. The reduction in bevel angle may result in a
greater risk of lack of fusion and would not be
compliant with the specification
c. The reduction in bevel angle would result in
requalification of all the welders
d. All options may apply
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Question 7
In accordance with the TWI Specification would it
be permissible to hard stamp the vessel’s
material for the purpose of material
identification?
a. Yes, any hard stamping is permitted providing
the information is on both ends of the material
b. No, hard stamping isn’t allowed in any
situation
c. Yes, hard stamping is permitted providing a
low stress concentration die is used.
d. No options are correct
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Question 8
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Question 9
During fit-up you notice that the longitudinal seams
have two different bevel angles on one joint, top
bevel 50°, bottom bevel 15°. Is this permitted in
accordance with TWI Specification?
While inspecting the completed vessel, you
notice that some of the longitudinal seams on
the main barrel section are in line with each
other, ie not offset:
a. No, under no situation shall different bevel
angles be permitted on a single V joint
b. Yes, providing the joint is welded either in the
overhead or vertical horizontal positions
c. No, the bevel angles stated are out of
specification
d. Yes, As long as there is access this would be
acceptable
a. This would be permitted providing the linear
misalignment doesn’t exceed 1.5mm
b. This is not permitted all longitudinal seams
shall be off set to each other by 90°
c. The TWI Specification makes no mention of
this requirement
d. This would be permitted providing the angular
misalignment doesn’t exceed 3°
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Copyright © TWI Ltd
2‐7
Question 10
The fabricator wishes to reduce welding time and
distortion on the longitudinal and circumferential
welds, which of the following will best achieve
this?
a. Single V butt joints, welded by the MMA
process
b. Double V butt joints, welded by the SAW
process
c. Double U butt joints, welded by the SAW
process
d. Heterogeneous welds
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2‐8
Section 3
Quality Assurance and Quality Control
3
Quality Assurance and Quality Control
3.1
Definitions
Before we consider what quality assurance and quality control are, let us first
define quality. This is best described as the fitness-for-purpose of a product,
service or activity.
Quality assurance comprises all the planned and systematic actions necessary
to provide adequate confidence that a product or service will satisfy given
requirements for quality. Quality control is described as the operational
techniques and activities that are used to fulfil requirements for quality.
Quality assurance therefore encompasses the plans and systems by which
confidence in a product is provided, ie all of the paperwork used to plan, control
and record activities: the documentation.
Quality control describes the activities which monitor the quality of the product.
These operational techniques include materials and dimensional checks,
inspection before, during and after welding, non-destructive testing, hydraulic
or leak testing, ie activities which check after the event that a specified activity
has been carried out correctly.
Quality assurance has been introduced to ensure that the activity ‘gets it right
the first time’, based on the principle that prevention is better than cure. This
can be achieved by planning and anticipating problems.
In order to satisfy this requirement, a documented quality system is needed
which sets out in a formal framework the basis of control for the critical
activities. This framework generally comprises four tiers of documentation, the
highest tier being the company quality manual, followed by quality systems,
quality plans and detailed manufacturing and inspection instructions.
3.1.1
Quality system
A quality system can be defined as:
The organisation structures, responsibilities, procedures,
resources for implementing quality management.
processes
and
The quality manual and support procedures document an organisation's quality
system.
3.1.2
Quality manual
A quality manual can be defined as:
A document setting out the general quality policies, procedures and practices of
an organisation.
The word ‘general’ is important in this definition. The quality manual is usually
the first indication a purchaser or prospective client has of a company's
approach to quality. This document should contain a statement of the
company's total commitment to quality by means of a quality policy statement
signed by the Chairman, MD or Chief Executive of the company. This policy
statement should be prominently displayed within the company.
WIS10-30816
Quality Assurance and Quality Control
3-1
Copyright © TWI Ltd
3.1.3
Procedure
A procedure can be defined as:
A document that describes how an activity is to be performed and by whom.
Note: A procedure is not a detailed work instruction such as a welding
procedure, but rather a statement of who does what and how: it describes the
corporate plan for achieving quality. However, there may be times when an
organisation needs to operate in a different way from the corporate system, for
example for a unique project or to satisfy a specific customer's requirements.
In these circumstances, an appropriate quality system can be documented in
the form of a project off-contract specific quality plan.
3.1.4
Quality plan
A quality plan can be defined as:
A document setting out the specific quality practices, resources and sequence of
activities relevant to a particular product, service, contract or project.
A quality plan is the corporate quality system suitably modified to reflect
specific equipments. It may comprise a project quality manual incorporating
appropriate sections from the corporate quality manual which apply. It is
generally a detailed document.
Project procedures may include:
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Existing procedures appropriate to the contract.
Existing procedures amended for the contract.
New procedures to meet new specific requirements of the contract.
Some contracts may well call for a combination of all three.
3.2
Quality system standards
Quality system standards specify the minimum requirements of quality systems
for application to specific products or services.
Standards are normally used for the following purposes:
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As guidance to an organisation introducing quality assurance.
As a basis for evaluating an organisation's quality system (assessment).
To specify the quality assurance requirements when invoked in a contract.
The most common standard in the UK is ISO 9000.
3.2.1
Quality records
A quality record is any document that specifies the inspection performed,
quantities inspected, results obtained, positive identification of the material
inspected to drawing or part number, the signature or stamp of the person
carrying out the inspection and date of inspection. Quality records may also
indicate the qualifications of personnel, calibration of equipment or other
records not directly related to the product.
WIS10-30816
Quality Assurance and Quality Control
3-2
Copyright © TWI Ltd
Questions that need to be addressed include:
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3.2.2
What quality records are to be maintained, eg received inspection reports,
NDT results, test certificates, final inspection reports and non-conformance
reports (including any feedback or corrective action generated)?
Where are the records filed and by whom?
How long are the quality records retained?
Are the quality records available to the customer for analysis and review?
Are records easily retrievable?
Is a suitable environment available to minimise deterioration or damage to
stored records?
Typical quality record contents
The Quality Record Package for a welded product is defined specifically for each
contract, but should include the following types of information:
a
b
c
d
e
f
g
h
i
j
k
l
Records of stage inspections in the form of check sheets or quality plans.
Non-conformity reports and concession records.
Where appropriate, as-built drawings.
Welding procedures.
Welder approvals.
Welding consumable records.
Weld history records.
NDT reports.
Heat treatment records.
Hydraulic and/or other testing records.
Where appropriate, material test certificates.
Final acceptance certificates.
WIS10-30816
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Copyright © TWI Ltd
3.2.3
What areas of a business need to be covered by ISO 9001?
ISO 9001 requires the following elements of a business to have set procedures:
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3.3
Management responsibility - who is responsible for what?
Quality system - how does the system operate?
Contract review - allows personnel to see what the requirement is and who
has been asked to do what.
Design review and control - ensures smooth passage from drawing board to
end product.
Documentation controls - make sure the correct documents are available.
Purchasing - make sure the right products and services are available.
Purchaser supplied product - make sure that purchased items are in a
satisfactory condition.
Product identification and traceability - what is it and where is it?
Process control - lets everyone know clearly how to make the product.
Inspection and test - describes how to inspect and test the product.
Inspection, measuring and test equipment - make sure the equipment used
is correct.
Inspection and test status - where is the product in the inspection cycle?
Control of non-conforming product - ensures incorrect product is not used.
Corrective action - finds the root cause of the problem and solves it.
Handling, storage, packing and delivery - don't damage it now it's made.
Quality records – fulfils the need for documented evidence that the company
meets specific requirements.
Internal quality audits - are quality activities performed as planned?
Training – the product cannot be manufactured effectively if people are not
adequately trained and qualified.
Servicing - if carried out by the company, effective procedures are required.
Statistical techniques - used to build-in product quality.
Auditing and documentation
Quality manuals, procedures, work instructions etc provide objective evidence
that the systems of control have been adequately planned.
The records and documentation generated by carrying out work in accordance
with these systems provide the evidence that the systems are being followed by
all. Systems of control, no matter how effective they are, will tend to
deteriorate because of human errors being made or perpetuated or due to
changes in the nature of the business.
In order to ensure that the systems are effective and being followed, as well as
to determine if changes are needed, it is necessary to monitor the systems.
This is achieved by auditing them and reviewing the results of the audit in order
to implement any changes.
3.3.1
What is an audit?
Quality audits examine
implementation.
a
quality
system
for
adequacy
and
correct
They are defined in BS 4778 Part 1 as:
Systematic and independent examinations to determine whether quality
activities and related results comply with planned arrangements and whether
these arrangements are implemented effectively and are suitable to achieve
objectives.
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Copyright © TWI Ltd
Auditing is carried out to provide objective evidence that the system is working
in accordance with the procedures. When an audit is complete the results are
analysed by management who must ensure that the quality policy is satisfied
and modify the quality system if necessary.
3.3.2
Which type of audit?
There are two levels of audit:
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3.3.3
A systems audit, which is quite superficial and simply examines the system
to confirm that it follows the quality manual and that procedures are in
place.
A compliance audit, which is an in-depth audit examining compliance with
procedures.
Auditing of documentation
A documentation audit is regarded as being a compliance audit, where
documentation is examined in depth.
Items to check in such an audit should include:
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Is all the documentation available?
Is the documentation schedule in accordance with contract or specification
requirements?
Does the documentation itself comply with contract or specification
requirements? For example, are the weld procedure and welders correctly
qualified?
Is the material composition correct?
Is the documentation legible?
Have all the interested parties, eg inspection department, independent third
party inspectors and client inspectors, signed off where required?
Have provisions been made for storage (which includes the ability to
retrieve documents and storage conditions preventing deterioration)?
Documentation audits should be carried out by the manufacturer/supplier as a
matter of course.
Customers will also frequently require access to carry out their own audits.
Remember that no job is finished until the paperwork is complete.
Failure of a documentation audit carried out by a client will often result in a
delay in payment, even though the component may have been delivered to the
client. There can often be a consequential financial penalty.
3.4
Quality requirements for welding
Within the international community, welding has been defined as a special
process which means that it must be controlled by specialist management and
utilise specialist personnel.
The welding co-ordination BS EN ISO 14731 and welding quality systems
standards BS EN ISO 3834 have been prepared in support of this ruling.
It is perceived that these standards will serve as references for other
application standards and be used as set criteria for the qualification of
fabricators.
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Quality Assurance and Quality Control
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Copyright © TWI Ltd
Currently there are a number of European Standards or codes that refer to
BS EN ISO 3834:
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EN 13445:2002: Unfired pressure vessels.
prEN 15085: Railway applications – Welding of railway vehicles and
components.
prEN 1090: Execution of steel structures.
EN 12732: 2000 Gas supply systems – Welding steel pipework – functional
requirements.
EN 12592: 2001 Water tube boilers and auxiliary installations.
National Structural Steelwork Specification for Building Construction (5th
Edition) (NSSSBC).
It is an increasingly common requirement for the fabricator to have a quality
system compliant with ISO 3834. This is to be specified as a condition of the
customer contract.
3.4.1
Qualification of welding fabricators – BS EN ISO 3834
BS EN ISO 3834 comprises five parts:
Part 1 - Guidance for use
This describes how the standard works.
Part 2 - Quality requirements for welding - Fusion welding of metallic
materials - Comprehensive quality system
This standard is suitable for use by a manufacturer or an assessment body, as a
supplement to ISO 9001 or 9002 providing detailed guidance on the
requirements that must be in place to adequately control welding.
Part 3 - Quality requirements for welding, Fusion welding of metallic
materials - Standard quality system
This standard can be applied where a documented quality system for the
control of welding is required but will not be used in conjunction with ISO 9001
or 9002.
Part 4 - Quality requirements for welding - Fusion welding of metallic
materials - Elementary system
This standard provides criteria appropriate for the control of welding when
either of the following applies:

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A quality system according to ISO 9001 is not to be applied.
The combination of selected welding processes, procedures and the final
welds are such that documented welding controls have minor importance in
respect to the overall integrity of the product.
Part 5 - Documents with which it is necessary to conform to claim
conformity to the quality requirements of BS EN ISO 3834-2, BS EN ISO
3834-3 or BS EN ISO 3834-4
This lists all other documents or standards that are required for compliance with
BS EN ISO 3834, such as specification and qualification of welding procedures,
approval testing of welders, etc.
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The manufacturer should select one of the three parts (2-4) specifying the
different levels of quality requirements, based on the following criteria:

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The extent and significance of safety-critical products;
The complexity of manufacture;
The range of products manufactured;
The range of different materials used;
The extent to which metallurgical problems may occur;
The extent to which manufacturing imperfections, eg misalignment,
distortion or weld imperfection, affect product performance.
This approach offers a cascading qualification; for
(comprehensive) also gives compliance for lower levels.
example,
Part
2
As previously stated, BS EN ISO 3834 is intended to complement, rather than
conflict with, quality systems established to meet the requirements of ISO 9001
and, in the case of a comprehensive quality system for welding fabrication (Part
2), requires in addition to ISO 9001 that specific procedures are used to control
the following:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Review of requirements.
Technical review.
Sub-contracting.
Welders and welding operators.
Welding co-ordination personnel.
Inspection and testing personnel.
Production and testing equipment.
Equipment maintenance.
Description of equipment.
Production planning.
Welding procedure specifications.
Qualification of welding procedures.
Batch testing of consumables (if required by contract).
Storage and handling of welding consumables.
Storage of parent material.
Post-weld heat treatment procedure.
Inspection and testing before, during and after welding.
Non-conformance and corrective actions.
Calibration or validation of measuring, inspection and testing equipment.
Identification during process (if required by contract).
Traceability (if required by contract).
Quality records (if required by contract).
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A company applying for certification to ISO 3834 will usually be required to
complete the following stages:
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Client returns preliminary enquiry.
Quotation.
Detailed forms sent to client.
Assessment team appointed by auditor.
Preliminary visit by auditor (not mandatory but common) to carry out a gap
analysis.
Document review by auditor to review procedures against BS EN ISO 3834.
On-site assessment conducted by auditor to demonstrate that the client has
accrued evidence that procedures are used and that these are overseen by
the welding co-ordination team.
Assessment recommendations made.
Certificate issued (5 year validity).
Surveillance (yearly).
This process, from application to issuing of the certificate, can take months to
complete.
3.4.2
Welding co-ordination
A key part of BS EN ISO 3834 is the definition of responsibilities of the welding
co-ordination personnel. ISO 14731 defines these personnel and the technical
knowledge that they require. The main role falls to the Responsible Welding Coordinator (RWC).
One or more personnel in a company may perform the welding co-ordination
function, but each of the requirements of BS EN ISO 3834 listed above will
require input from the welding co-ordination team.
Table 1 in BS EN ISO 14731 gives guidance for those tasks which may require a
welding co-ordinator input. The technical knowledge required from the coordinator will obviously depend upon the complexity of the product.
The standard defines three levels of knowledge and experience:
1
2
3
Comprehensive: Equivalent to the level of an International/European
Welding Engineer.
Specific: Equivalent to the level of an International/European Welding
Technologist.
Basic: Equivalent to the level of an International/European Welding
Specialist.
It can be seen that the three levels of technical knowledge are defined to match
with the three levels of quality requirements given in Parts 2-4 of BS EN ISO
3834.
The IIW route is not mandatory; there are in fact three possible routes to
demonstrate technical knowledge:
1
2
3
IIW qualification and experience (via interview).
Interview to assess knowledge without IIW qualification (professional
review in 3834 audit).
Sub-contract to an external resource with appropriate knowledge and
experience; again, an interview is required (it would be expected that the
external resource will be familiar with the company applying for certification
and will be contracted to visit regularly).
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3.5
Calibration/validation of welding equipment
Faulty equipment compromises the quality of work. It follows that any
equipment used in production, or for welder and procedure approval tests,
should be in a sound condition in all respects in order to avoid breakdown
during production or testing.
One important point to note is the accuracy of meters and the repeatability of
the machine's controls in relation to output performance. Welding current
connections and return leads on all arc welding equipment should be checked
for tightness prior to commencing welding; failure to do so may lead to voltage
losses affecting arcing conditions.
Where semi-automatic gas shielded processes are used, care should also be
taken to ensure that the wire feeding systems are repeatable and accurate.
Additionally, flowmeters controlling shielding and purging gases are expected to
be calibrated.
This activity is collectively known as validation.
A requirement in many industries during the welding operation is the use of a
calibrated meter(s) to check the welding current, arc voltages, travel speed
and, on occasion, wire feed speed.
In addition, it must be ensured that the welders are using the correct gas, the
electrode wires are of the correct composition and the preheat temperature and
location have been applied in accordance with the welding procedure
requirements.
In the case of manual metal arc (MMA) and submerged-arc welding (SAW),
attention should be paid to any special drying requirements for fluxes or
covered electrodes and also the conditions they are kept in prior to use. The
use of a written procedure for storage and handling of consumables is
recommended and records of humidity and temperature may be required to be
kept.
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Se ct ion 4
Code s a n d St a n da r ds
4
Code s a n d St an da r ds
The cont r ol of qualit y in a fabricat ion and welding sit uat ion is achiev ed by
wor king t o com pany procedur es and codes of const ruct ion or st andards. The
lat t er m ay be int ernat ional, nat ional, com pany’s own or specific t o t he part icular
client or cont ract .
Com pany pr ocedur es ar e usually covered in qualit y m anuals t he scope of which
m ay vary widely depending upon t he size of com pany, it s range of wor k, it s
wor king pract ices and m any ot her fact ors.
4 .1
Com pa ny m a nu a ls
4 .1 .1
Qua lit y a ssu r a nce m a nua l
Qualit y assurance is defined in I S0 9000 as; part of qualit y m anagem ent
focused on pr oviding confidence t hat qualit y requirem ent s will be fulfilled.
Essent ially what t he QA m anual set s out is how t he com pany is organised, t o
lay down t he responsibilit ies and aut horit y of t he various depart m ent s, how
t hese depart m ent s int erlink. The m anual usually covers all aspect s of t he
com pany st ruct ure, not j ust t hose aspect s of m anufact ure.
4 .1 .2
Qua lit y cont r ol m a nu a l
Qualit y cont rol is defined in I SO 9000 as; part of qualit y m anagem ent focused
on fulfilling qualit y requirem ent s.
The QC m anual will be t he m anual m ost oft en referr ed t o by t he SWI as it will
spell out in det ail how different depart m ent s and operat ions ar e organised and
cont r olled.
Typical exam ples would be: pr oduct ion and cont rol of dr awings, how m at erials
and consum ables are purchased, how w elding procedur es ar e produced, et c.
Essent ially all operat ions t o be carried out wit hin t he organisat ion will have
cont r ol procedur es laid down.
I n part icular it will lay down how t he I n spe ct ion funct ion, whet her visual,
dim ensional or NDT, will be perform ed, inspect ion being defined as t he act ivit y
of m easuring, exam ining and t est ing charact erist ics of a pr oduct or ser vice and
com paring t hese t o a specified requirem ent . Such requirem ent s are laid down in
codes of pract ice and st andards.
4 .2
Audit ing
Audit ing is a t erm originat ing from account ancy pract ice which involves an
independent account ant checking t he account s of a com pany t o see if t he
account s ar e fair and accurat e. A sim ilar checking process is now widely
pract ised in m anufact uring and const ruct ion indust ries and inspect ion per sonnel
will be involved in t he carr ying out of t his operat ion.
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Differ ent t ypes of audit s m ay be perfor m ed:



Full audit of a com pany, usually carried out by a t hird part y such as a
Cert ifying Aut horit y, checking t he com pany for t he award of a QA
accr edit at ion syst em such as I SO 9000 or ASME st am p.
Maj or audit by a pot ent ial cust om er prior t o placem ent of a large cont ract .
This is usually carried out t o dem onst rat e t he com pany has all t he
necessary facilit ies, plant , m achinery, personnel and qualit y syst em s in
place t o enable t hem t o successfully com plet e t he cont ract .
Part audit s carried out as ongoing dem onst rat ion t hat t he qualit y syst em is
wor king properly.
An exam ple of t he lat t er case w ould be wher e a Senior I nspect or is r esponsible
for signing- off t he dat a book or r elease cert ificat e for a product . Aft er checking
t hat all t he necessar y docum ent s are in t he package and t hat t hey have been
corr ect ly com plet ed and approv ed wher e necessary , t he SWI w ould look at a
part of t he j ob – a beam , a piece of pipew ork et c and cr osscheck against t he
drawings, m ill cert ificat es, inspect ion report s et c t hat all com ply wit h t he j ob
requirem ent s.
4 .3
Code s a nd st a n da r ds
I t is not necessary for t he I nspect or t o car ry a wide range of codes and
st andards in t he perfor m ance of his/ her dut ies. Norm ally t he specificat ion or
m or e precisely t he cont ract specificat ion is t he only docum ent required.
How ev er t he cont ract specificat ion m ay reference support ing codes and
st andards and t he inspect or should know w her e t o access t hese norm at ive
docum ent s.
The following is a list of definit ions relat ing t o codes and st andards which t he
I nspect or m ay com e acr oss whilst car rying inspect ion dut ies
4 .3 .1
D e finit ion s
N or m a t ive docu m e nt :
Provides rules, guidelines or charact erist ics for act ivit ies or t heir r esult s.
The t erm norm at ive docum ent is generic and covers docum ent s such as
st andards, t echnical specificat ions, codes of pract ice and r egulat ions.*
St a nda r d
Docum ent est ablished by consensus and approv ed by a r ecognised body.
A st andard pr ovides, for com m on and r epeat ed use, guidelines, rules, and
charact erist ics for act ivit ies or t heir result s, aim ed at t he achievem ent of t he
opt im um degree of order in a given cont ext .*
H a r m onise d st a nd a r d s
St andards on t he sam e subj ect approved by differ ent st andardising bodies, t hat
est ablish int erchangeabilit y of product s, processes and services, or m ut ual
underst anding of t est result s or inform at ion provided according t o t hese
st andards*
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Code of pr a ct ice
Docum ent t hat r ecom m ends pract ices or procedures for t he design,
m anufact ure, inst allat ion, m aint enance, ut ilisat ion of equipm ent , st ruct ures or
product s.
A code of pract ice m ay be a st andard, part of a st andard or independent of a
st andard.*
Re gu la t ion
Docum ent pr oviding binding legislat ive rules t hat is adopt ed by an aut horit y.*
Aut h or it y
Body ( r esponsible for st andards and regulat ions legal or adm inist rat ive ent it y
t hat has specific t asks and com posit ion) t hat has legal power s and right s.*
Re gu la t or y a ut hor it y
Aut horit y responsible for pr eparing or adopt ing regulat ions.*
Enfor ce m e nt a ut hor it y
Aut horit y responsible for enforcing regulat ions.*
Spe cifica t ion
A docum ent st at ing requirem ent s, needs or expect at ions.
A specificat ion could cover bot h physical and t echnical requirem ent s ie visual
inspect ion, NDT, Mechanical t est ing et c. essent ially full dat a and it s support ing
m edium . Specificat ions are generally im plied or obligat ory.
Pr oce dur e
Specified way t o carry out an act ivit y or a process.* Usually it is a writ t en
descript ion of all essent ial param et er s and pr ecaut ions t o be observ ed when
applying a t echnique t o a specific applicat ion following an est ablished st andard,
code or specificat ion
I nst r uct ion
Writ t en descript ion of t he precise st eps t o be followed based on an est ablished
procedur e, st andard, code or specificat ion.
Qua lit y pla n
A docum ent specifying which procedur es and associat ed resources shall be
applied by whom and w hen t o a specific proj ect , pr oduct , process or cont ract .*
*
I SO I EC Guide 2 – St andardisat ion and relat ed act ivit ies – General
vocabulary.
* * EN I SO 9000 – 2000 – Qualit y m anagem ent syst em s – Fundam ent als and
vocabulary.
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4 .4
Sum m a r y
Applicat ion of t he requirem ent s of t he qualit y m anuals, t he st andards and codes
of pract ice ensur e t hat a st ruct ur e or com ponent will have an accept able level
of qualit y and be fit for t he int ended purpose.
Applying t he requirem ent s of a st andard, code of pract ice or specificat ion can
be a pr oblem for t he inexperienced I nspect or. Confidence in applying t he
requirem ent s of one or all of t hese docum ent s t o a specific applicat ion only
com es wit h use ov er a period of t im e.
I f in doubt t he I nspect or m ust always r efer t o a higher aut horit y in order t o
avoid confusion and pot ent ial problem s.
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Se ct ion 5
Fe - C St e e ls
5
Fe - C St e e ls
Pure iron is v ery soft and expensive t o m anufact ure and t hus has lim it ed
pract ical engineering applicat ions. How ev er , as we’ve already seen, as ferr ous
alloys can go t hr ough different phase changes depending on com posit ion and
t em perat ur e, t he pr opert ies and part icularly t he st r engt h, duct ilit y and
t oughness can be t ailored t hrough alloying and t herm al cycling ( heat t reat m ent
or welding for exam ple) .
Of all t he alloying elem ent s used in st eels, by far t he m ost im port ant one is
carbon ( C) and st eels are defined as iron alloys cont aining less t han 2% C.
Fer rous alloys of m or e t han 2% carbon cont ent on t he ot her hand are called
cast irons.
Many ot her elem ent s can also be present in st eels, bot h int ent ionally added
alloying elem ent s and r esidual elem ent s pr esent from ore or scrap m et al used
in t he st eelm aking process.
5 .1
St e e l t e r m inology
The t erm inology used t o describe and specify different st eel product s can be
confusing as t hese can be based on a com binat ion of:








Product form ( sheet , plat e, bar, sect ions, pipe or wire) .
Deoxidat ion pract ice ( killed, sem i- killed) .
Manufact uring rout e such as cast , forged, r olled, ext ruded.
Heat t reat m ent such as annealed, norm alised and quench and t em per ed,
which are used t o achieve propert ies.
Cleanliness level in t erm s of im purit ies such as sulphur and phosphor ous.
Finishing m et hods such as cold rolled or hot r olled.
Presence or not of cor rosion prot ect ion coat ings.
And so on.
To add t o t he confusion, different indust ry sect or s use different nom enclat ures
and definit ions t o r efer t o t he sam e alloys. A sim plified t erm inology is used her e
which is widely used and is relevant t o w elding, but be awar e t hat ot her
t erm inologies also exist .
I n a broad sense, non- st ainless st eels can be divided int o t wo m aj or groups:
Carbon st eel ( also called C- Mn st eels, depending on Mn level) and low alloy
st eels. This nom enclat ure is used in Am erican st andards ( Am erican I r on and
St eel I nst it ut e and The Societ y of Aut om ot ive Engineering) and in m odified
for m s in Eur opean st andards as w ell.
5 .1 .1
Ca r bon st e e ls
I n m any indust ry sect ors, carbon st eel is t he usual descript ion used t o refer t o
any st eel t hat is not st ainless. Carbon is t he single m ost im port ant alloying
elem ent in st eel and a wide range of propert ies is possible sim ply by changing
it s cont ent . St r engt h can be increased v er y cost effect ively by r et aining m ore
carbon in t he com posit ion ( rem em ber, carbon is already present from t he
prim ary st eelm aking process and is in fact r em ov ed as part of st eel r efining) .
How ev er, when welded it is well recognized t hat HAZ t oughness decr eases and
risk of cracking during welding increases wit h carbon addit ion and welding
becom es m or e challenging. Surprisingly t hough, in som e part icular applicat ions
such as in welded rail t rack s t his t rade- off can be overcom e and st eels which
are oft en of eut ect ic com posit ion wit h carbon cont ent of 0.76% are used! !
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As shown below, hardness and st r engt h can be achieved sim ply by increasing
t he carbon cont ent of t he alloy. This however com es at a cost , not only in t erm s
of welding but also in t erm s of m echanical propert ies as duct ilit y and t oughness
also det eriorat e wit h increasing carbon cont ent .
Carbon st eels can be divided ( broadly) int o plain carbon and carbon- m anganese
st eels:
Pla in ca r bon st e e ls are t he m ost widely used st eel t ype. These ar e usually
specified based on carbon cont ent ( exam ple, AI SI 1010 and 1018 carbon st eels
have t arget carbon cont ent s of approxim at ely 0.1 and 0.18, r espect ively) and
are lim it ed t o a m axim um of 1% m anganese. The m icr ost ruct ures of plain
carbon st eels are based around t he t herm odynam ic equilibrium m icrost ruct ures
of ferrit e and pearlit e.
Ca r bon – m a nga ne se ( C- M n ) st e e ls ar e sim ilar t o plain carbon st eels ex cept
t hat C- Mn st eels have higher Mn cont ent s of bet ween 1 and 1.65 w eight % .
Manganese is used for deoxidat ion ( t o r em ov e oxygen from t he m elt during
st eelm aking) , as a solid solut ion st rengt hener and also can have t he effect of
lowering t he duct ile t o brit t le t ransit ion t em perat ur e. How ev er , addit ion of
m anganese also increases t he hardenabilit y of st eels which could be a drawback
when welding as will be shown lat er in t his sect ion.
5 .1 .2
Low Alloy st e e ls
Som e alloying elem ent s increase t he hardenabilit y of st eels, t hat is, t hey delay
t he t ransform at ion fr om aust enit e t o t he equilibrium m icrost ruct ur es of fer rit e
and pearlit e t o longer t im es, t hus giving m ore opport unit y for non- equilibrium
m icrost ruct ures such as m art ensit e t o form during cooling. Alloys specified
based on elem ent addit ions t o increase hardenabilit y t o achieve designat ed
st rengt h, duct ilit y and t oughness r equirem ent s ar e called low alloy st eels. I n
general, t ot al alloy cont ent does not exceed 5% .
Mart ensit e is achieved wit h a sufficient level of carbon or ot her elem ent s and a
sufficient ly rapid cooling rat e. I t has high st rengt h and hardness but can be
very brit t le, so a soft ening ( t em pering) heat t reat m ent is norm ally applied t o
im prove t oughness during t he m anufact uring process. This is not always
possible aft er welding and t hese st eels r equire special precaut ions during
welding t o obt ain good enough propert ies in t he HAZ and t o avoid hydrogen
cracking.
N ot e : I n som e indust ry sect or s st ainless st eels are refer r ed t o as alloy st eels
( m inim um of 10% alloying) , which is probably why low- alloy- st eel is used t o
describe st eels wit h high hardenabilit y ( quenched and t em per ed for exam ple)
as t hese hav e m uch lower alloy cont ent com pared t o st ainless grades.
Com paring wit h C- Mn st eels howev er, t hese are r elat ively high alloyed st eel
grades wit h m uch higher hardenabilit y.
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5 .1 .3
H igh st r e ngt h low a lloy st e e ls
For t he par ent m at erial, an alt ernat ive appr oach t o increase st rengt h wit hout
increasing carbon cont ent is grain refinem ent which not only increases st rengt h
but also increases t oughness. This fam ily of fine grained high st rengt h st eels
( up t o 560MPa yield) wit h low carbon and lean general com posit ion are called
high st rengt h low alloy st eels.
Cont rary t o low- alloy- st eels which can in fact be quit e highly alloyed, HSLA
st eels are t ruly low alloyed st eels and t he st r engt h is achieved t hrough
refinem ent of t he m icr ost ruct ure rat her t han by significant alloying addit ions.
For t he sam e st r engt h lev el, an HSLA alloy will have a m uch leaner com posit ion
t o it s C- Mn equivalent . The m icrost ruct ur e of HSLA st eels is st ill generally ferrit e
and pearlit e but will usually cont ain very sm all am ount s of pearlit e.
The m anufact uring rout es t o achieve t he necessar y m icrost ruct ur e r efinem ent
wer e cover ed in Sect ion 6 ( Heat t r eat m ent of st eels) .
To r e f r e sh you r m e m or y
HSLA st eels r ely on ver y sm all alloying addit ions of vanadium , niobium and/ or
t it anium and cont rolled rolling as well as defined and narrow t em perat ur e
ranges. Because t he addit ions of V, Nb and Ti are so sm all t hese ar e also called
m icro- alloyed st eels.
Part icularly in t he oil and gas indust ry, a slight variat ion of t he cont rolled r olling
process is used where m icro- alloying is used t o obt ain a fine- grain st ruct ur e
during t he hot rolling process followed by accelerat ed cooling at t he end of t he
hot r olling process t o pr om ot e a bainit ic or acicular fer rit e m icrost ruct ure. These
alloys ar e called Therm o- m echanically cont r olled process ( TMCP) st eels.
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Se ct ion 6
D e st r u ct ive Te st in g
6
D e st r u ct ive Te st in g
Eur opean Welding St andards require t est coupons t hat ar e m ade for w elding
procedur e qualificat ion t est ing t o be subj ect ed t o non- dest ruct ive t est ing and
t hen dest ruct ive t est ing.
The t est s are called dest ruct ive t est s because t he welded j oint is dest r oy ed
when various t ypes of t est piece are t aken fr om it .
Dest ruct ive t est s can be divided int o 2 groups, t hose used t o:


Measure a m echanical propert y
Assess t he j oint qualit y
– qu a nt it a t ive t e st s
– qu a lit a t ive t e st s
Mechanical t est s are quant it at ive because a quant it y is m easured – a
m echanical propert y such as t ensile st rengt h, hardness and im pact t oughness.
Qualit at ive t est s ar e used t o v erify t hat t he j oint is free fr om defect s – t hey ar e
of sound qualit y, exam ples of t hese ar e bend t est s, m acr oscopic ex am inat ion
and fract ur e t est s ( fillet fract ur e and nick- br eak) .
6 .1
Te st t y pe s, t e st pie ce s a nd t e st obj e ct ive s
Various t ypes of m echanical t est s are used by m at erial m anufact urers and
suppliers t o verify t hat plat es, pipes, forgings, et c. have t he m inim um propert y
values specified for part icular grades.
Design engineers use t he m inim um propert y v alues list ed for part icular grades
of m at erial as t he basis for design and t he m ost cost - effect ive designs are
based on an assum pt ion t hat welded j oint s have pr opert ies t hat are no wor se
t han t hose of t he base m et al.
The quant it at ive ( m echanical) t est s t hat are carried out for welding procedur e
qualificat ion are int ended t o dem onst rat e t hat t he j oint propert ies sat isfy design
requirem ent s.
The em phasis in t he following sub- sect ions is on t he dest ruct ive t est s and t est
m et hods t hat ar e widely used for w elded j oint s.
6 .1 .1
Tr a n sve r se t e nsile t e st s
Te st obj e ct ive
Welding procedur e qualificat ion t est s always r equire t ransv er se t ensile t est s t o
show t hat t he st r engt h of t he j oint sat isfies t he design crit erion.
Te st spe cim e n s
A t ransv erse t ensile t est piece t ypical of t he t ype specified by Eur opean Welding
St andards is shown below.
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Parallel
lengt h
St andards, such as EN 895, t hat specify dim ensions for t ransv er se t ensile t est
pieces r equire all excess w eld m et al t o be r em ov ed and t he surface t o be fr ee
from scrat ches.
Test pieces m ay be m achined t o repr esent t he full t hickness of t he j oint but for
very t hick j oint s it m ay be necessary t o t ak e several t ransverse t ensile t est
specim ens t o be able t o t est t he full t hickness.
Te st m e t hod
Test specim ens are accurat ely m easured befor e t est ing. Specim ens are t hen
fit t ed int o t he j aws of a t ensile t est ing m achine and subj ect ed t o a cont inually
increasing t ensile for ce unt il t he specim en fract ures.
The t ensile st rengt h ( Rm ) is calculat ed by dividing t he m axim um load by t he
cr oss- sect ional area of t he t est specim en - m easured before t est ing.
The t est is int ended t o m easur e t he t e n sile st r e ngt h of t h e j oin t and t hereby
show t hat t he basis for design, t he base m et al propert ies, rem ains t he valid
crit erion.
Acce pt a nce cr it e r ia
I f t he t est piece breaks in t he weld m et al, it is accept able provided t he
calculat ed st rengt h is not less t han t he m inim um t ensile st r engt h specified,
which is usually t he m inim um specified for t he base m et al m at erial grade.
I n t he ASME I X code, if t he t est specim en br eaks out side t he weld or fusion
zone at a st ress abov e 95% of t he m inim um base m et al st rengt h t he t est r esult
is accept able.
6 .1 .2
All- w e ld t e nsile t e st s
Te st obj e ct ive
Ther e m ay be occasions when it is necessary t o m easure t he weld m et al
st rengt h as part of welding procedure qualificat ion – part icularly for elevat ed
t em perat ur e designs.
The t est is carried out in order t o m easure not only t ensile st r engt h but also
yield ( or proof st r engt h) and t ensile duct ilit y.
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All weld t ensile t est s are also regularly carried out by w elding consum able
m anufact urers t o verify t hat elect rodes and filler wires sat isfy t he t ensile
propert ies specified by t he st andard t o which t he consum ables are cert ified.
Te st spe cim e ns
As t he nam e indicat es, t est specim ens are m achined from w elds par allel wit h
t heir longit udinal axis and t he specim en gauge lengt h m ust be 100% weld
m et al.
Round t ensile specim en from a welding
procedure qualificat ion t est piece.
Round t ensile specim en from an elect rode
classificat ion t est piece.
Te st m e t h od
Specim ens are subj ect ed t o a cont inually increasing force in t he sam e way t hat
t ransv er se t ensile specim ens are t est ed.
Yield ( Re) or proof st r ess ( Rp) ar e m easured by m eans of an ext ensom et er t hat
is at t ached t o t he parallel lengt h of t he specim en and is able t o accurat ely
m easur e t he ext ension of t he gauge lengt h as t he load is increased.
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Typical load ext ension curv es and t heir principal charact erist ics ar e shown
below.
Load- ext ension curve for a st eel t hat
shows a dist inct yield point at t he elast ic
lim it .
Load- ext ension curve for a st eel ( or
ot her m et al) t hat does not show a
dist inct yield point ; proof st ress is a
m easure of t he elast ic lim it .
Tensile duct ilit y is m easured in t wo ways:
1
2
% elongat ion of t he gauge lengt h ( A% ) .
% reduct ion of ar ea at t he point of fract ure ( Z% ) .
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The figures below illust rat e t hese t w o duct ilit y m easur em ent s.
Necking!
6 .1 .3
I m pa ct t ough ne ss t e st s
Te st obj e ct ive
Charpy V not ch t est pieces hav e
for assessing resist ance t o brit t le
and propagat e, a crack from a
subj ect ed t o an im pact load. The
im pa ct t ough ne ss.
becom e t he int ernat ionally accept ed m et hod
fract ur e by m easuring t he energy t o init iat e,
sharp not ch in a st andard sized specim en
va lue a chie ve d is k now n a s t he not ch or
Design engineers need t o ensur e t hat t he t oughness of t he st eel t hat is used for
a part icular it em will be high enough t o avoid brit t le fract ur e in service and so
im pact specim ens are t est ed at a t em perat ur e t hat is relat ed t o t he design
t em perat ur e for t he fabricat ed com ponent .
C- Mn and low alloy st eels undergo a sharp change in t heir resist ance t o brit t le
fract ur e as t heir t em perat ure is lowered so t hat a st eel t hat m ay have very
good t oughness at am bient t em perat ur e m ay show ext r em e brit t leness at subzer o t em perat ures, as illust rat ed in following figure.
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Tr a nsit ion r a n ge
I m pa ct e ne r gy ( Joules)
Uppe r she lf e ne r gy
D uct ile fr a ct ur e
( 0 % cr yst a llinit y)
Low e r she lf e ne r gy
Br it t le fr a ct ur e
( 1 0 0 % cr y st a llinit y)
Te st t e m pe r a t ur e , °C
The t ransit ion t em perat ure is defined as t he t em perat ur e m id- way bet ween t he
upper shelf ( m axim um t oughness) and lower shelf ( com plet ely brit t le) . I n t he
abov e t he t ransit ion t em perat ur e is –20°C.
Te st spe cim e ns
The dim ensions for t est specim ens have been st andardised int ernat ionally and
are shown below for full siz e d spe cim e ns. Ther e ar e also st andard dim ensions
for sm aller sized specim ens, for exam ple 10m m x 7.5m m and 10m m x 5m m .
Charpy V not ch t est piece dim ensions for full sized specim ens.
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Specim ens ar e m achined fr om w elded t est plat es wit h t he not ch posit ion
locat ed in different locat ions according t o t he t est ing requirem ent s but t ypically
in t he cent r e of t he w eld m et al and at posit ions acr oss t he HAZ – as shown
below.
Typical not ch posit ions for Charpy V not ch t est specim ens from double V but t
welds.
Te st m e t h od
Test specim ens ar e cooled t o t he specified t est t em perat ur e by im m ersion in an
insulat ed bat h cont aining a liquid t hat is held at t he t est t em perat ure.
Aft er allowing t he specim en t em perat ure t o st abilise for a few m inut es it is
quickly t ransfer red t o t he anvil of t he t est m achine and a pendulum ham m er
quickly released so t hat t he specim en experiences an im pact load behind t he
not ch.
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The m ain feat ur es of an im pact t est m achine ar e shown below.
I m pact specim en on t he anvil showing t he
ham m er posit ion at point of im pact
I m pact t est ing m achine
Charpy V not ch t est pieces
– before and aft er t est ing
The energy absorbed by t he ham m er when it st rikes each t est specim en is
shown by t he posit ion of t he ham m er point er on t he scale of t he m achine.
Energy values ar e given in Joules ( or ft - lbs in US specificat ions) .
I m pact t est specim ens ar e t ak en in t riplicat e ( 3 specim ens for each not ch
posit ion) as t here is always som e degr ee of scat t er in t he r esult s, part icularly
for w eldm ent s.
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Acce pt a nce cr it e r ia
Each t est r esult is recorded and an average value calculat ed for each set of
t hree t est s. These values are com par ed wit h t he values specified by t he
applicat ion st andard or client t o est ablish whet her specified requirem ent s have
been m et .
Aft er im pact t est ing, exam inat ion of t he t est specim ens pr ovides addit ional
inform at ion about t heir t oughness charact erist ics and m ay be added t o t he t est
report :


% cr yst allinit y – t he % of t he fract ur e face t hat has cryst alline appearance
which indicat es brit t le fr act ure; 100% indicat es com plet ely brit t le fract ure.
Lat er al expansion – t he increase in widt h of t he back of t he specim en
behind t he not ch – as indicat ed below; t he larger t he value t he t ougher t he
specim en.
A specim en t hat exhibit s ext rem e brit t leness will show a clean break. Bot h
halves of t he specim en having a com plet ely flat fract ure face wit h lit t le or no
lat eral expansion.
A specim en t hat exhibit s very good t oughness will show only a sm all degr ee of
crack ext ension, wit hout fract ure and a high value of lat eral expansion.
6 .1 .4
H a r dne ss t e st ing
Te st obj e ct ive s
The hardness of a m et al is it s’ r esist ance t o plast ic deform at ion det er m ined by
m easuring t he r esist ance t o indent at ion by a part icular t ype of indent er .
A st eel weldm ent wit h hardness above a cert ain m axim um m ay be suscept ible
t o cracking, eit her dur ing fabricat ion or in ser vice, and welding procedur e
qualificat ion t est ing for cert ain st eels and applicat ions t hat require t he t est w eld
t o be hardness sur vey ed t o ensure t hat ar e no r egions of t he weldm ent t hat
exceed t he m axim um specified hardness.
Specim ens pr epar ed for m acroscopic exam inat ion can also be used for t aking
hardness m easurem ent s at various posit ions of t he weldm ent – refer r ed t o as a
ha r dne ss sur v e y.
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Te st m e t h ods
Ther e ar e 3 widely used m et hods for hardness t est ing:
1
2
3
Vickers hardness t est
Rockw ell hardness t est
Brinell hardness t est
uses a square- base diam ond pyram id indent er.
uses a diam ond cone indent er or st eel ball.
uses a ball indent er.
The hardness value being given by t he size of t he indent at ion produced under a
st andard load, t he sm aller t he indent at ion, t he harder t he m et al.
The Vickers m et hod of t est ing is illust rat ed below.
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Bot h Vicker s and Rock well m et hods ar e suit able for carrying out hardness
surv eys on specim ens prepared for m acr oscopic exam inat ion of weldm ent s.
A t ypical hardness surv ey requires t he indent er t o m easur e t he hardness in t he
base m et al ( on bot h sides of t he weld) , in t he weld m et al and across t he HAZ
( on bot h sides of t he w eld) .
The Brinell m et hod gives an indent at ion t hat is t oo large t o accurat ely m easur e
t he hardness in specific regions of t he HAZ and is m ainly used t o m easur e
hardness of base m et als.
A t ypical hardness sur v ey ( using Vickers hardness indent er) is shown below:
Hardness values are shown on t est r eport s as a num ber followed by let t ers
indicat ing t he t est m et hod, for exam ple:
6 .1 .5
240HV10
= hardness 240, Vicker s m et hod, 10kg indent er load.
22HRC
= hardness 22, Rockw ell m et hod, diam ond cone indent er
( scale C) .
238HBW
= 238 hardness, Brinell m et hod, t ungst en ball indent er.
Cr a ck t ip ope n ing displa ce m e nt ( CTOD ) t e st in g
Te st obj e ct ive
Charpy V not ch t est ing enables engineers t o m ake j udgem ent s about risks of
brit t le fract ur e occurring in st eels, but a CTOD t est m easures a m at erial
propert y - fr a ct u r e t ou ghne ss.
Fract ur e t oughness dat a enables engineers t o car ry out fract ur e m echanics
analyses such as:


Calculat ing t he size of a crack t hat would init iat e a brit t le fract ur e under
cert ain st ress condit ions at a part icular t em perat ure.
The st ress t hat would cause a cert ain sized crack t o give a brit t le fract ure at
a part icular t em perat ur e.
This dat a is essent ial for m aking an appropriat e decision when a crack is
discovered during inspect ion of equipm ent t hat is in- service.
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Te st spe cim e n s
A CTOD specim en is prepared as a rect angular ( or squar e) shaped bar cut
t ransv er se t o t he axis of t he but t weld. A V not ch is m achined at t he cent re of
t he bar, which will be coincident wit h t he t est posit ion - weld m et al or HAZ.
A shallow saw cut is t hen put int o t he bot t om of t he not ch and t he specim en is
t hen put int o a m achine t hat induces a cy clic bending load unt il a shallow
fat igue crack init iat es fr om t he saw cut .
The specim ens are r elat ively large – t ypically having a cross sect ion B x 2B and
lengt h ~ 10B ( B = full t hickness of t he weld) . The t est piece det ails are shown
below.
Te st m e t h od
CTOD specim ens are usually t est ed at a t em perat ur e below am bient and t he
t em perat ur e of t he specim en is cont rolled by im m er sion in a bat h of liquid t hat
has been cooled t o t he r equired t est t em perat ur e.
A load is applied t o t he specim en t o cause bending and induce a concent rat ed
st ress at t he t ip of t he crack and a clip gauge, at t ached t o t he specim en across
t he m out h of t he m achined not ch, gives a reading of t he increase in widt h of
t he m out h of t he cr ack as t he load is gradually increased.
For each t est condit ion ( posit ion of not ch and t est t em perat ure) it is usual
pract ice t o carr y out t hr ee t est s.
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Below illust rat es t he m ain feat ures of t he CTOD t est .
Fract ur e t oughness is expr essed as t he dist ance t hat t he crack t ip opens
wit hout init iat ion of a br it t le crack.
The clip gauge enables a chart t o be generat ed showing t he increase in widt h of
t he crack m out h against applied load from which a CTOD value is calculat ed.
Acce pt a nce cr it e r ia
An applicat ion st andard or client m ay specify a m inim um CTOD v alue t hat
indicat es duct ile t earing. Alt ernat ively, t he t est m ay be for inform at ion so t hat a
value can be used for an engineering crit ical assessm ent .
A ver y t ough st eel weldm ent will allow t he m out h of t he crack t o open widely by
duct ile t earing at t he t ip of t he crack wher eas a very brit t le weldm ent will t end
t o fract ur e when t he applied load is quit e low and wit hout any ext ension at t he
t ip of t he crack .
CTOD values are expressed in m illim et res - t ypical values m ight be < < ~ 0.1m m
= brit t le behaviour; > ~ 1m m = v er y t ough behaviour.
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6 .1 .6
Be nd t e st ing
Te st obj e ct ive
Bend t est s are rout inely t aken fr om w elding procedur e qualificat ion t est pieces
and som et im es hav e t o be t ak en from welder qualificat ion t est pieces.
Subj ect ing specim ens t o bending is a sim ple m et hod of v erifying t hat t here ar e
no significant flaws in t he j oint . Som e degr ee of duct ilit y is also dem onst rat ed.
Duct ilit y is not act ually m easur ed but is dem onst rat ed t o be sat isfact ory if t est
specim ens can wit hst and being bent wit hout fract ure or fissur es above a cert ain
lengt h.
Te st spe cim e n s
Ther e ar e 4 t ypes of bend specim en:
Fa ce be nd
Specim en t aken wit h axis t ransver se t o but t welds up t o ~ 12m m t hickness and
bent so t hat t he face of t he weld is on t he out side of t he bend ( face in t ension) .
Root be nd
Test specim en t aken wit h axis t ransverse t o but t welds up t o ~ 12m m t hickness
and bent so t hat t he r oot of t he w eld is on t he out side of t he bend ( root in
t ension) .
Side be nd
Test specim en t aken as a t ransverse slice ( ~ 10m m ) from t he full t hickness of
but t welds > ~ 12m m and bent so t hat t he full j oint t hickness is t est ed ( side in
t ension) .
Longit udin a l be nd
Test specim en t ak en wit h axis parallel t o t he longit udinal axis of a but t weld;
specim en t hickness is ~ 12m m and t he face or r oot of w eld m ay be t est ed in
t ension.
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Te st m e t hod
Bend t est s for w elding procedur e qualificat ion ( and welder qualificat ion) are
usually guided bend t est s.
Guided m eans t hat t he st rain im posed on t he specim en is uniform ly cont rolled
by being bent ar ound a for m er wit h a cert ain diam et er.
The diam et er of t he for m er used for a part icular t est is specified in t he code,
having been det erm ined by t he t ype of m at er ial t hat is being t est ed and t he
duct ilit y t hat can be expect ed from it aft er w elding and any PWHT.
The diam et er of t he for m er is usually expressed as a m ult iple of t he specim en
t hickness and for C- Mn st eel it is t ypically 4t ( t is t he specim en t hickness) but
for m at erials t hat have lower t ensile duct ilit y t he radius of t he form er m ay be
great er t han 10t .
The st andard t hat specifies t he t est m et hod will specify t he m inim um bend
angle t hat t he specim en m ust experience and t his is t ypically 120- 180°.
Acce pt a nce cr it e r ia
Bend t est pieces should exhibit sat isfact or y soundness by not showing cracks or
any signs of significant fissures or cavit ies on t he out side of t he bend.
Sm all indicat ions less t han about 3m m in lengt h m ay be allowed by som e
st andards.
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6 .2
Fr a ct ur e t e st s
6 .2 .1
Fille t w e ld fr a ct u r e s
Te st obj e ct ive
The qualit y/ soundness of a fillet weld can be assessed by fract uring t est pieces
and exam ining t he fract ure surfaces.
This m et hod for assessing t he qualit y of fillet welds m ay be specified by
applicat ion st andards as an alt ernat ive t o m acr oscopic exam inat ion.
I t is a t est m et hod t hat can be used for w elder qualificat ion t est ing according t o
Eur opean St andards but is not used for welding procedure qualificat ion t o
Eur opean St andards.
Te st spe cim e n s
A t est weld is cut int o short lengt hs ( t ypically 50m m ) and a longit udinal not ch
is m achined int o t he specim en as shown below. The not ch pr ofile m ay be
square, V or U shaped.
Te st m e t hod
Specim ens ar e m ade t o fract ure t hr ough t heir t hroat by dynam ic st rok es
( ham m ering) or by pressing, as shown below. The welding st andard or
applicat ion st andard will specify t he num ber of t est s ( t ypically 4) .
Acce pt a nce cr it e r ia
The st andard for welder qualificat ion, or applicat ion st andard, will specify t he
accept ance crit eria for im perfect ions such as lack of penet rat ion int o t he r oot of
t he j oint and solid inclusions and porosit y t hat are visible on t he fract ur e
surfaces.
Test r eport s should also give a descript ion of t he appearance of t he fract ure and
locat ion of any im perfect ion
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But t w e ld fr a ct u r e s ( nick - br e a k t e st s)
Te st obj e ct ive
The obj ect ive of t hese fr act ure t est s is t he sam e as for fillet fract ur e t est s.
These t est s ar e specified for w elder qualificat ion t est ing t o European St andards
as an alt ernat ive t o radiography. They are not used for w elding procedur e
qualificat ion t est ing t o EU St andards.
Te st spe cim e ns
Test specim ens ar e t ak en fr om a but t weld and not ched so t hat t he fract ure
pat h will be in t he cent ral region of t he weld. Typical t est piece t ypes are shown
below.
Te st m e t h od
Test pieces ar e m ade t o fract ure by ham m ering or t hr ee- point bending.
Acce pt a nce cr it e r ia
The st andard for welder qualificat ion, or applicat ion st andard, will specify t he
accept ance crit eria for im perfect ions such as lack of fusion, solid inclusions and
por osit y t hat are visible on t he fract ure sur faces.
Test r eport s should also give a descript ion of t he appearance of t he fract ure and
locat ion of any im perfect ion.
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6 .3
M a cr oscopic e x a m in a t ion
Transv erse sect ions from but t and fillet welds are r equired by t he EU St andards
for welding procedur e qualificat ion t est ing and m ay be required for som e w elder
qualificat ion t est ing for assessing t he qualit y of t he welds.
This is considered in det ail in a separat e sect ion of t hese cour se not es.
Macr o exam inat ion
Micro exam inat ion
Obj e ct ive s




Det ect ing weld defect s. ( m acr o) .
Measuring grain size. ( m icro) .
Det ect ing brit t le st ruct ures, precipit at es.
Assessing resist ance t oward brit t le fract ur e, cold cracking and corr osion
sensit ivit y.
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Eur ope a n St a n da r ds for D e st r u ct ive Test M e t h ods
The following St andards ar e specified by t he Eur opean Welding St andards for
dest ruct ive t est ing of welding procedur e qualificat ion t est welds and for som e
welder qualificat ion t est welds.
BS EN I SO 9 0 1 6
Dest ruct ive t est s on w elds in m et allic m at erials – I m pact t est s – Test specim en
locat ion, not ch orient at ion and exam inat ion.
BS EN I SO 4 1 3 6
Dest ruct ive t est s on w elds in m et allic m at erials – Transverse t ensile t est .
BS EN I SO 5 1 7 3 + A1
Dest ruct ive t est s on w elds in m et allic m at erials – Bend t est s.
BS EN I SO 1 7 6 3 9
Dest ruct ive t est s on w elds in m et allic m at erials – Macroscopic and m icroscopic
exam inat ion of w eld.
BS EN I SO 6 8 9 2 - 1
Met allic m at erials t em perat ur e.
Tensile t est ing. Part 1:
Met hod of t est at am bient
BS EN I SO 6 8 9 2 - 2
Tensile t est ing of m et allic m at erials. Part 2: Met hod of t est at elevat ed
t em perat ur es.
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Destructive Testing Objective
When this presentation has been completed you
should be able to:
 Recognise a wide range of mechanical tests
and their purpose.
 Make calculations using formulae and tables to
determine various values of strength,
toughness, hardness and ductility.
Destructive Testing
Section 6
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Destructive Testing Definitions
Destructive Tests
Destructive tests
includes
 Bend test.
 Impact test.
 Tensile test.
 Hardness test.
 Macro/micro
examination.
What is Destructive Testing?
The destruction of a
welded unit or by
cutting out selected
specimens from the
weld is carried out to
check the mechanical
properties of the joint
materials. They can
be produced to:
3 x Toughness
(Charpy V
notch)
2 x Ductile
(Bend test)
2 x Strength
(transverse
tensile)
 Approve welding procedures (BS EN 15614).
 Approve welders (BS EN 287).
 Production quality control.
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Qualitative and Quantitative Tests
The following mechanical tests have units and are termed
quantitative tests to measure mechanical properties
of the joint.
 Tensile tests (transverse welded joint, all weld metal).
 Toughness testing (Charpy, Izod, CTOD).
 Hardness tests (Brinell, Rockwell, Vickers).
The following mechanical tests have no units and are
termed qualitative tests for assessing weld quality.
 Macro testing.
 Bend testing.
 Fillet weld fracture testing.
 Butt weld nick-break testing.
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Definitions
Mechanical Properties of metals are related
to the amount of deformation which metals can
withstand under different circumstances of force
application.





Malleability
Ductility
Toughness
Hardness
Tensile Strength
Ability of a material to
withstand deformation
under static compressive
loading without rupture
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6‐1
Definitions
Definitions
Mechanical Properties of metals are related
to the amount of deformation which metals can
withstand under different circumstances of force
application.
Mechanical Properties of metals are related
to the amount of deformation which metals can
withstand under different circumstances of force
application.










Malleability
Ductility
Toughness
Hardness
Tensile Strength
Ability of a material
undergo plastic deformation
under static tensile loading
without rupture. Measurable
elongation and reduction in
cross section area
Malleability
Ductility
Toughness
Hardness
Tensile Strength
Ability of a material to
withstand bending or the
application of shear
stresses by impact loading
without fracture.
Copyright © TWI Ltd
Copyright © TWI Ltd
Definitions
Definitions
Mechanical Properties of metals are related
to the amount of deformation which metals can
withstand under different circumstances of force
application.
Mechanical Properties of metals are related
to the amount of deformation which metals can
withstand under different circumstances of force
application.










Malleability
Ductility
Toughness
Hardness
Tensile Strength
Measurement of a materials
surface resistance to
indentation from another
material by static load
Malleability
Ductility
Toughness
Hardness
Tensile Strength
Measurement of the
maximum force required to
fracture a materials bar of
unit cross-sectional area in
tension
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Mechanical Test Samples
Tensile specimens
Destructive Testing
Welding Procedure Qualification Testing
CTOD specimen
Top of fixed pipe
2
Typical positions for test
pieces
Specimen type
3 Macro + hardness
Transverse tensile
Bend test
specimen
Charpy
specimen
Fracture fillet
specimen
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4
Position
5
2, 4
Bend tests
2, 4
Charpy impact tests
3
Additional tests
3
5
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6‐2
Mechanical Testing
Hardness Testing
Definition
 Measurement of resistance of a material
against penetration of an indenter under a
constant load.
 There is a direct correlation between UTS and
hardness.
Hardness Testing
Hardness tests
 Brinell.
 Vickers.
 Rockwell.
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Hardness Testing
Objectives
 Measuring hardness in different areas of a
welded joint.
 Assessing resistance toward brittle fracture, cold
cracking and corrosion sensitivity.
Information to be supplied on the test report
 Material type.
 Location of indentation.
 Type of hardness test and load applied on the
indenter.
 Hardness value.
Hardness Testing
Usually the hardest region
1.5 to
3mm
Fusion
line or
fusion
boundary
HAZ
Hardness test methods
Vickers
Rockwell
Brinell
Typical designations
240 HV10
Rc 22
200 BHN-W
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Copyright © TWI Ltd
Vickers Hardness Test
Typical location of the indentations
Butt weld from
one side only
Vickers Hardness Test
Vickers hardness tests
 Indentation body is a square based diamond
pyramid (136° included angle).
 The average diagonal (d) of the impression is
converted to a hardness number from a table.
 It is measured in HV5, HV10 or HV025.
Indentation
Adjustable shutters
Diamond indentor
Butt weld from
both side
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Copyright © TWI Ltd
6‐3
Vickers Hardness Test Machine
Brinell Hardness Test
 Hardened steel ball of given diameter is
subjected for a given time to a given load.
 Load divided by area of indentation gives
Brinell hardness in kg/mm2.
 More suitable for on site hardness testing.
30KN
Ø=10mm
steel ball
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Copyright © TWI Ltd
Rockwell Hardness Test
Rockwell B
Portable Hardness Test
Rockwell C
1KN
1.5KN
Ø=1.6mm
steel ball
 Dynamic and very portable hardness test.
 Accuracy depends on the condition of the
test/support surfaces and the support of the
test piece during the test.
 For more details, see ASTM E448.
120° Diamond
cone
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Copyright © TWI Ltd
Mechanical Testing
Charpy V-Notch Impact Test
Weld metal
Fusion Line (FL)
FL+2mm
FL+5mm
Parent material
Objectives
 Measuring impact strength in different weld joint areas.
 Assessing resistance toward brittle fracture.
Impact Testing
Information to be supplied on the test report
 Material type.
 Notch type.
 Specimen size.
 Test temperature.
 Notch location.
 Impact Strength Value.
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐4
Charpy V-Notch Impact Test
Specimen
Pendulum
(striker)
Anvil
(support)
Charpy V-Notch Impact Test Specimen
Specimen dimensions according ASTM E23
ASTM: American Society of Testing Materials
Copyright © TWI Ltd
Copyright © TWI Ltd
Charpy Impact Test
10 mm
2 mm
22.5°
100% Brittle
Mn < 1.6 % increases
toughness in steels,
and lower energy
input used.
Machined notch
8 mm
Ductile/Brittle Transition Curve
Fracture surface
100% bright
crystalline
brittle fracture
Temperature range
Ductile fracture
47 Joules
Transition range
Ductile/Brittle
transition point
100% Ductile
28 Joules
Machined notch
Brittle fracture
Large reduction
in area, shear
lips
Randomly torn,
dull gray
fracture surface
- 50
- 40
- 30
Energy absorbed
- 20
- 10
0
Testing temperature - Degrees Centigrade
Three specimens are normally tested at each temperature
Copyright © TWI Ltd
Comparison Charpy
Impact Test Results
Impact Energy Joules
Room Temperature
-20oC Temperature
1.
197 Joules
1.
49 Joules
2.
191 Joules
2.
53 Joules
3.
186 Joules
3.
51 Joules
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Charpy Impact Test
Reporting results
 Location and orientation of notch.
 Testing temperature.
 Energy absorbed in joules.
 Description of fracture (brittle or ductile).
 Location of any defects present.
 Dimensions of specimen.
Average = 191 Joules Average = 51 Joules
The test results show the specimens carried out at room
temperature absorb more energy than the specimens
carried out at -20oC.
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐5
Mechanical Testing
Tensile Testing
Tensile Testing
Copyright © TWI Ltd
UTS Tensile Test
Copyright © TWI Ltd
Tensile Tests
Rm
ReH
ReL
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Tensile Test
Rp 0.2% - Proof stress
Refers to materials which do not have a defined
yielding such as aluminium and some steels.
Copyright © TWI Ltd
Copyright © TWI Ltd
Tensile Tests
Different tensile tests
 Transverse tensile.
 All-weld metal tensile test.
 Cruciform tensile test.
 Short tensile test (through thickness test).
Copyright © TWI Ltd
6‐6
Tensile Test
Transverse Joint Tensile Test
All-weld metal tensile
specimen
Objective
Measuring the overall strength of the weld joint.
Information to be supplied on the test report
 Material type.
 Specimen type.
 Specimen size (see QW-462.1).
 UTS.
 Location of final rupture.
Transverse tensile
specimen
Copyright © TWI Ltd
Copyright © TWI Ltd
Transverse Joint Tensile Test
Transverse Tensile Test
Maximum load applied = 220 kN
Cross sectional area = 25 mm X 12 mm
UTS =
Weld on plate
UTS =
Weld on pipe
Multiple cross joint
specimens
Maximum load applied
csa
220 000
25mm X 12mm
UTS = 733.33 N/mm2
Copyright © TWI Ltd
Transverse Tensile Test
Reporting results:
 Type of specimen eg reduced section.
 Whether weld reinforcement is removed.
 Dimensions of test specimen.
 The ultimate tensile strength in N/mm2, psi or
Mpa.
 Location of fracture.
 Location and type of any flaws present if any.
Copyright © TWI Ltd
All-Weld Metal Tensile Test
BS EN ISO 6892-1
All Weld Metal Tensile Testing
Direction of the test*
Tensile test piece cut along weld specimen
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐7
All-Weld Metal Tensile Test
All-Weld Metal Tensile Test
Gauge length
Original gauge length = 50mm
Increased gauge length = 64
Object of test
 Ultimate tensile
strength.
 Yield strength.
 Elongation
%(ductility).
Elongation % = Increase of gauge length
X 100
Original gauge length
Elongation % = 14
50
X 100
Increased gauge length
Elongation = 28%
Copyright © TWI Ltd
All-Weld Metal Tensile Test
Two marks are made
Copyright © TWI Ltd
All-Weld Metal Tensile Test
Two marks are made
Gauge length 50mm
Gauge length 50mm
During the test, yield and tensile strength are recorded
The specimen is joined and the marks are re-measured
During the test, Yield & Tensile strength are recorded
The specimen is joined and the marks are re-measured
Force Applied
Increased gauge length 75mm
Increased gauge length 75mm
A measurement of 75mm will give Elongation of 50%
Copyright © TWI Ltd
All-Weld Metal Tensile Test
A measurement of 75mm will give Elongation of 50%
Copyright © TWI Ltd
STRA (Short Transverse
Reduction Area)
Reporting results
 Type of specimen eg reduced section.
 Dimensions of test specimen.
 The UTS, yield strength in N/mm2, psi or Mpa.
 Elongation %.
 Location and type of any flaws present if any.
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐8
STRA Test
STRA Test
Probable freedom from
tearing in any joint type
Original CSA
STRA %
Reduction
of CSA
Reduced CSA
Copyright © TWI Ltd
Mechanical Testing
20
Some risk in highly restrained
joints eg node joint, joints
between sub-fabs
15
Some risk in moderately
restrained joints eg box
columns
10
Some risk in lightly restrained
joints T-joints eg I-beams
Copyright © TWI Ltd
Macro Preparation
Purpose
To examine the weld cross-section to give assurance that:
 The weld has been made in accordance with the WPS.
 The weld is free from defects.
Specimen preparation
 Full thickness slice taken from the weld (typically
~10mm thick).
 Width of slice sufficient to show all the weld and HAZ on
both sides plus some unaffected base material.
 One face ground to a progressively fine finish (grit sizes
120 to ~ 400).
 Prepared face heavily etched to show all weld runs & all
HAZ.
 Prepared face examined at up to x5 (& usually
photographed for records).
 Prepared face may also be used for a hardness survey.
Macro/Micro Examination
Copyright © TWI Ltd
Micro Preparation
Purpose
To examine a particular region of the weld or HAZ in order to:
 To examine the microstructure.
 Identify the nature of a crack or other imperfection.
Specimen preparation
 A small piece is cut from the region of interest (typically up
to ~ 20mm x 20mm).
 The piece is mounted in plastic mould and the surface of
interest prepared by progressive grinding (to grit size 600
or 800).
 Surface polished on diamond impregnated cloths to a
mirror finish
 Prepared face may be examined in as-polished condition
and then lightly etched.
 Prepared face examined under the microscope at up to ~
100 – 1000X.
Copyright © TWI Ltd
Copyright © TWI Ltd
Macro/Micro Examination
Object
 Macro/microscopic examinations are used to
give a visual evaluation of a cross-section of a
welded joint.
 Carried out on full thickness specimens.
 The width of the specimen should include HAZ,
weld and parent plate.
 They maybe cut from a stop/start area on a
welders approval test.
Copyright © TWI Ltd
6‐9
Macro/Micro Examination
Will reveal
 Weld soundness.
 Distribution of inclusions.
 Number of weld passes.
 Metallurgical structure of weld, fusion zone
and HAZ.
 Location and depth of penetration of weld.
 Fillet weld leg and throat dimensions.
Macro/Micro Examination
Macro
 Visual examination for
defects.
 Cut transverse from the
weld.
 Ground and polished
P400 grit paper.
 Acid etch using 5-10%
nitric acid solution.
 Wash and dry.
 Visual evaluation under
5x magnification.
 Report on results.
Micro
 Visual examination for
defects and grain
structure.
 Cut transverse from a
weld.
 Ground and polished P1200
grit paper, 1µm paste.
 Acid etch using 1-5% nitric
acid solution.
 Wash and dry.
 Visual evaluation under
100-1000x magnification.
 Report on results.
Copyright © TWI Ltd
Copyright © TWI Ltd
Metallographic Examination
Metallographic Examination
Objectives
 Detecting weld defects (macro).
 Measuring grain size (micro).
 Detecting brittle structures, precipitates, etc.
 Assessing resistance toward brittle fracture, cold
cracking and corrosion sensitivity.
Macro examination
Micro examination
Information to be supplied on the test report
 Material type.
 Etching solution.
 Magnification.
 Grain size.
 Location of examined area.
 Weld imperfections (macro).
 Phase, constituents, precipitates (micro).
Copyright © TWI Ltd
Copyright © TWI Ltd
Mechanical Testing
Bend Tests
Object of test
To determine the soundness of the weld zone. Bend
testing can also be used to give an assessment of weld
zone ductility.
There are three ways to perform a bend test:
Bend Testing
Root bend
Face bend
Side bend
Side bend tests are normally carried out on welds over
12mm in thickness.
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐10
Bending Test
Bending Test Methods
Types of bend test for welds
(acc BS EN ISO 5173):
Root/face
bend
t up to 12 mm
Thickness of material - t
t over 12 mm
Side bend
Guided bend test
Copyright © TWI Ltd
Bend Testing
Side
bend
Face
bend
Defect indication
generally this
specimen would
be unacceptable
Root
bend
Acceptance for
minor ruptures
on tension
surface
depends upon
code
requirements.
Copyright © TWI Ltd
Mechanical Testing
Wrap around bend test
Copyright © TWI Ltd
Bend Tests
Reporting results
 Thickness and dimensions of specimen.
 Direction of bend (root, face or side).
 Angle of bend (90°, 120°, 180°).
 Diameter of former (typical 4T).
 Appearance of joint after bending eg type and
location of any flaws.
Copyright © TWI Ltd
Fillet Weld Fracture Tests
Object of test
 To break open the joint through the weld to
permit examination of the fracture surfaces.
 Specimens are cut to the required length.
 A saw cut approximately 2mm in depth is
applied along the fillet welds length.
 Fracture is usually made by striking the
specimen with a single hammer blow.
 Visual inspection for defects.
Fillet Weld Fracture Testing
Copyright © TWI Ltd
Copyright © TWI Ltd
6‐11
Fillet Weld Fracture Tests
Fillet Weld Fracture Tests
Hammer
2mm
Notch
This fracture indicates
lack of fusion
Fracture should break weld saw cut to root
This fracture has
occurred saw cut to root
Lack of penetration
Copyright © TWI Ltd
Copyright © TWI Ltd
Fillet Weld Fracture Tests
Reporting results
 Thickness of parent material.
 Throat thickness and leg lengths.
 Location of fracture.
 Appearance of joint after fracture.
 Depth of penetration.
 Defects present on fracture surfaces.
Mechanical Testing
Nick-Break Testing
Copyright © TWI Ltd
Copyright © TWI Ltd
Nick-Break Test
Object of test
 To permit evaluation of any weld defects
across the fracture surface of a butt weld.
 Specimens are cut transverse to the weld.
 A saw cut approximately 2mm in depth is
applied along the welds root and cap.
 Fracture is usually made by striking the
specimen with a single hammer blow.
 Visual inspection for defects.
Copyright © TWI Ltd
Nick-Break Test
Notch cut by hacksaw
3 mm
19 mm
3 mm
Approximately 230 mm
Weld reinforcement
may or may not be
removed
Copyright © TWI Ltd
6‐12
Nick-Break Test
Alternative nick-break
test specimen, notch
applied all way around
the specimen
Lack of root penetration
or fusion
Nick-Break Test
Reporting results
 Thickness of parent material.
 Width of specimen.
 Location of fracture.
 Appearance of joint after fracture.
 Depth of penetration.
 Defects present on fracture surfaces.
Inclusions on fracture
line
Copyright © TWI Ltd
Summary of Mechanical Testing
We test welds to establish minimum levels of
mechanical properties and soundness of the
welded joint
We divide tests into qualitative and quantitative methods:
Quantitative: (Have units)
 Hardness (VPN & BHN)
 Toughness (Joules &
ft.lbs)
 Strength (N/mm2 &
PSI, MPa)
 Ductility/Elongation
(E%)
Qualitative: (Have no
units)
 Macro tests
 Bend tests
 Fillet weld fracture
tests
 Butt nick-break tests
Copyright © TWI Ltd
Hydrostatic Test
Test procedure
 Blank off all openings with solid flanges.
 Use correct nuts and bolts, not G clamps.
 Two pressure gauges on independent tapping
points should be used.
 For safety purposes bleed all the air out.
 Pumping should be done slowly (no dynamic
pressure stresses).
 Test pressure - see relevant standards (PD
5500, ASME VIII). Usually 150% design
pressure.
 Hold the pressure for minimum 30 minutes.
Copyright © TWI Ltd
Copyright © TWI Ltd
Hydrostatic Test
Under pressure leakage proof test
Vessel configuration
 The test should be done after any stress relief.
 Components that will not stand the pressure
test (eg flexible pipes, diaphragms) must be
removed.
 The ambient temperature MUST be above 0°C
(preferably 15-20°C).
Copyright © TWI Ltd
Hydrostatic Test
What to look for
 Leaks (check particularly around seams and
nozzle welds)!
 Dry off any condensation.
 Watch the gauges for pressure drop.
 Check for distortion of flange faces, etc.
Copyright © TWI Ltd
6‐13
Mechanical Testing
Mechanical Testing
As part of your remit as a Senior Welding
Inspector, visits to the test house are common,
witnessing mechanical testing of weld procedures
and welder qualifications in C Mn steel.
Any Questions
?
In addition, verifying the accompanying
documentation is also a major part of your role.
Therefore, your knowledge of the TWI specification
and the use of it is essential to your role.
Copyright © TWI Ltd
Question 1
You notice at the test house that root and face
bends are being conducted with a 50% reduction
in the former diameter than that stated in the
specification. What difference would this make to
the testing conditions?
a. This should make no difference as long as the
bend is to the correct angle
b. This is common practice when reinforcement
is left in place
c. This would put excessive stress on the
specimen
d. No options are correct
Copyright © TWI Ltd
Question 3
Testing has just been completed on a single sided butt
weld procedure, 10mm thick, PA position using the MMA
process. Which mechanical tests would you expect to find
within the documentation?
a. 1 transverse tensile, two transverse side bends, impact
tests 1 set of 3, Hardness test one specimen and
macro examination
b. 2 transverse tensile, two transverse bends-1root and 1
face bends, impact tests 1 set of 3, Hardness test one
specimen and macro examination
c. 2 transverse tensile, two transverse root and 1 face
bends, hardness test one specimen and macro
examination
d. 2 transverse tensile, two transverse side bends, impact
tests 1 set of 3, Hardness test one specimen and
macro examination
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 2
Continuing with the witnessing of bend testing,
you notice that the excess weld metal has not
been removed. Are there any consequences
attached to this practice?
a. When bends are tested in this manner, the test is
much more accurate as all the weld is under test
b. The excess weld metal is only removed if it is
excessive
c. The excess weld metal could give rise to stresses
d. Only the part in contact with the former requires
the excess weld metal to be removed
Copyright © TWI Ltd
Question 4
You are checking the test report for a transverse
tensile test on a 16mm butt weld with a UTS value of
460N/mm². Which of the following sets of tensile
samples would fail the test?
a. Test 1 failed in parent metal at 414 N/mm², test 2
failed in weld metal at 555N/mm²
b. Test 1 failed in parent metal at 420 N/mm², test 2
failed in weld metal at 480N/mm²
c. Test 1 failed in parent metal at 435 N/mm², test 2
failed in weld metal at 498N/mm²
d. Test 2 failed in weld metal at 498N/mm², test 1
failed in parent metal at 435 N/mm²
Copyright © TWI Ltd
6‐14
Question 5
Charpy impact tests have been conducted on a
16mm single V butt joint. Which of the following
set of results would meet the specification?
a. Average of set 30
value 20 joules
b. Average of set 40
value 32 joules
c. Average of set 38
value 35 joules
d. Average of set 42
value 28 joules
joules, lowest individual
joules, lowest individual
joules, lowest individual
joules, lowest individual
Question 6
A welder qualifies in C Mn steel, 10mm thick,
MMA process using low hydrogen electrodes, PC
position using DC- polarity. Which one of the
following is the welder not qualified for?
a. C mn steel, 20mm thick, MMA process, rutile
electrode, PB position, DCb. C mn steel, 6mm thick, MMA process, rutile
electrode, PA position, DCc. C mn steel, 15mm thick, MMA process, low
hydrogen electrode, PC position, DCd. C mn steel, 15mm thick, MMA process, rutile
electrode, PE position, DC-
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 7
A charpy impact test is devised to test samples
at different temperatures. What does this hope
to establish?
a.
b.
c.
d.
A transition range from ductile to brittle
The Rm of the material
The Re of the material
The relationship between hardness and
tensile strength
Question 8
The point at which the Rm is reached in a tensile
test is also referred to as the:
a.
b.
c.
d.
Yield point
UTS
A%
Gauge length
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Copyright © TWI Ltd
Question 9
If a tensile test specimen fails to meet the
required value, what action can be taken?
a. Two more test welds are required which will
require complete testing
b. One more test sample can be submitted
c. If the specimen is large enough, two more
tests can be done
d. As many test welds as required can be
submitted until the tests meet the
specification
Copyright © TWI Ltd
Question 10
In a procedure qualification in 10m thick material
welded in the PF position when impacts are not
specified, which position(s) is the procedure
qualified for?
a.
b.
c.
d.
PA, PC
PF, PG
All positions
PF only
Copyright © TWI Ltd
6‐15
Se ct ion 7
H e a t Tr e a t m e n t
7
H e a t Tr e a t m en t
The heat t reat m ent given t o a part icular grade of st eel by t he st eelm aker/
supplier should be shown on t he m at erial t est cert ificat e and m ay be referr ed t o
as t he supply condit ion.
Welding inspect or s m ay need t o r efer t o m at erial t est cert ificat es and it is
appropriat e t hat t hey be fam iliar wit h t he t er m inology t hat is used and have
som e under st anding of t he principles of som e of t he m ost com m only applied
heat t r eat m ent s.
Welded j oint s m ay need t o be subj ect ed t o heat t reat m ent aft er welding
( PWHT) and t he t asks of m onit oring t he t her m al cycle and checking t he heat
t reat m ent r ecords are oft en delegat ed t o welding inspect or s.
7 .1
H e a t t r e a t m e nt of st e e l
The m ain supply condit ions for w eldable st eels are:
As r olle d, hot r olle d, hot f in ish e d
Plat e is hot rolled t o finished size and allowed t o air cool; t he t em perat ur e at
which rolling finishes m ay vary fr om plat e t o plat e and so st rengt h and
t oughness propert ies vary and are not opt im ised:
Applie d t o:
Relat ively t hin, lower st rengt h C- st eel.
The r m o- m e ch a n ica l cont r olle d
t he r m o- m e ch a n ica lly r olle d
pr oce ssin g
( TM CP) ,
cont r ol
r olle d,
St eel plat e given precisely cont r olled t hickness r educt ions during hot rolling
wit hin carefully cont r olled t em perat ure ranges; final rolling t em perat ur e is also
car efully cont r olled;
Applie d t o
Relat ively t hin, high st rengt h low alloy st eels ( HSLA) and for som e st eels wit h
good t oughness at low t em perat ur es, eg cryogenic st eels.
N or m a lise d
Aft er working t he st eel ( rolling or forging) t o size, it is heat ed t o ~ 900°C and
t hen allowed t o cool in air t o am bient t em perat ure; t his opt im ises st r engt h and
t oughness and gives uniform pr opert ies fr om it em t o it em for a part icular grade
of st eel;
Applie d t o
C- Mn st eels and som e low alloy st eels.
Que n ch e d a n d t e m pe r e d
aft er w or king t he st eel ( rolling or forging) t o size, it is heat ed t o ~ 900°C and
t hen cooled as quickly as possible by quenching in wat er or oil; aft er quenching,
t he st eel m ust be t em per ed ( soft ened) t o im prove t he duct ilit y of t he asquenched st eel:
Applie d t o
Som e low alloy st eels t o give higher st r engt h, t oughness or wear resist ance.
WI S10- 30816
Heat Treat m ent
7- 1
Copyright © TWI Lt d
Solut ion a nn e a le d/ h e a t t r e a t e d
Aft er hot or cold working t o size, st eel heat ed t o ~ 1100°C and rapidly cooled by
quenching int o wat er t o prevent any carbides or ot her phases from for m ing:
Applie d t o
Aust enit ic st ainless st eels such as 304 and 316 grades.
Ann e a le d
Aft er w or king t he st eel ( pressing or forging et c) t o size, it is heat ed t o ~ 900°C
and t hen allowed t o cool in t he furnace t o am bient t em perat ur e; t his reduces
st rengt h and t oughness but im proves duct ilit y:
Applie d t o
C- Mn st eels and som e low alloy st eels.
Figure 7.1- 7.6 show t he t herm al cycles for t he m ain supply condit ions and
subsequent heat t r eat m ent t hat can be applied t o st eels.
7 .2
Post w e ld he a t t r e a t m e nt ( PW H T)
Post w eld heat t reat m ent has t o be applied t o som e w elded st eels t o ensure
t hat t he propert ies of t he w eldm ent will be suit able for t heir int ended
applicat ions.
The t em per at ure at w hich PWHT is carried out is usually well below t he
t em perat ur e where phase changes can occur ( not e 1) , but high enough t o allow
residual st resses t o be r elieved quickly and t o soft en ( t em per) any har d regions
in t he HAZ.
Ther e ar e m aj or benefit s of r educing residual st ress and ensuring t hat t he HAZ
hardness is not t oo high for part icular st eels wit h cert ain service applicat ions.
Exam ples of t hese benefit s are:



I m proved t he r esist ance of t he j oint t o brit t le fract ure.
I m proved t he r esist ance of t he j oint t o st ress corr osion cracking.
Enables welded j oint s t o be m achined t o accurat e dim ensional t olerances.
Because t he m ain reason for ( and benefit of) PWHT is t o reduce residual
st resses, PWHT is oft en called st r e ss r e lie f.
N ot e : Ther e are circum st ances when a welded j oint m ay need t o be norm alised
t o r est or e HAZ t oughness. However, t hese ar e relat ively rare circum st ances and
it is necessar y t o ensure t hat w elding consum ables are car efully select ed
because norm alising will significant ly reduce w eld m et al st rengt h.
WI S10- 30816
Heat Treat m ent
7- 2
Copyright © TWI Lt d
7 .3
PW H T t he r m a l cycle
The applicat ion st andard/ code will specify when PWHT is required t o give
benefit s # 1 or # 2 above and also give guidance about t he t herm al cycle t hat
m ust be used.
I n order t o ensur e t hat a PWHT cy cle is carried it in accordance wit h a part icular
code, it is essent ial t hat a PWHT pr ocedur e is prepared and t hat t he following
param et er s are specified:




7 .3 .1
Maxim um heat ing rat e.
Soak t em perat ur e range.
Minim um t im e at t he soak t em perat ure ( soak t im e) .
Maxim um cooling rat e.
H e a t ing r a t e
This m ust be cont r olled t o av oid large t em perat ur e differ ences wit hin t he
fabricat ed it em . Large differences in t em perat ure ( large t herm al gradient s) will
produce large st resses and t hese m ay be high enough t o cause dist ort ion ( or
ev en cracking) .
Applicat ion st andards usually require cont r ol of t he m axim um heat ing rat e when
t he t em perat ur e of t he it em is above ~ 300°C. This is because st eels st art t o
show significant loss of st rengt h abov e t his t em perat ur e and ar e m ore
suscept ible t o dist ort ion if t here ar e large t herm al gradient s.
The t em perat ur e of t he fabricat ed it em m ust be m onit ored during t he t herm al
cycle and t his is done by m eans of t herm ocouples at t ached t o t he sur face at a
num ber of locat ions r epresent ing t he t hickness range of t he it em .
By m onit oring furnace and it em t em perat ur es t he rat e of heat ing can be
cont r olled t o ensur e com pliance wit h code requirem ent s a t a ll posit ion s
w it h in t he it e m .
Maxim um heat ing rat es specified for C- Mn st eel depend on t hickness of t he
it em but t end t o be in t he range ~ 60 t o ~ 200°C/ h.
7 .3 .2
Soa k t e m pe r a t ur e
The soak t em perat ure specified by t he code depends on t he t ype of st eel and
t hus t he t em perat ur e range r equired t o r educe r esidual st resses t o a low level.
C and C- Mn st eels require a soak t em perat ur e of ~ 600°C wher eas som e low
alloy st eels ( such as Cr- Mo st eels used for elevat ed t em perat ur e service)
require higher t em perat ures – t ypically in t he range ~ 700 t o ~ 760°C.
N ot e : Soak t em perat ur e is an essent ial variable for a WPQR. Thus, it is very
im port ant t hat t he it is cont r olled wit hin t he specified lim it s ot herwise it m ay be
necessary t o carr y out a new WPQ t est t o validat e t he propert ies of t he it em
and at worst it m ay not be fit - for- purpose.
WI S10- 30816
Heat Treat m ent
7- 3
Copyright © TWI Lt d
7 .3 .3
Soa k t im e
I t is necessary t o allow t im e for all t he welded j oint s t o experience t he specified
t em perat ur e t hr oughout t he full j oint t hickness.
The t em perat ur e is m onit ored by sur face- cont act t herm ocouples and it is t he
t hickest j oint of t he fabricat ion t hat governs t he m inim um t im e for t em perat ur e
equalisat ion.
Typical specified soak t im es ar e 1h per 25m m t hickness.
7 .3 .4
Cooling r a t e
I t is necessary t o cont r ol t he rat e of cooling from t he PWHT t em perat ure for t he
sam e r eason t hat heat ing rat e needs t o be cont rolled – t o avoid dist ort ion ( or
cracking) due t o high st resses fr om t herm al gradient s.
Codes usually specify cont rolled cooling t o ~ 300°C. Below t his t em perat ure t he
it em can be wit hdrawn from a furnace and allowed t o cool in air because st eel is
relat ively st rong and is unlikely t o suffer plast ic st rain by any t em perat ur e
gradient s t hat m ay dev elop.
Figure 7.6 is a t ypical PWHT t her m al cycle.
7 .4
H e a t t r e a t m e nt f ur n a ce s
I t is im port ant t hat oil and gas- fired furnaces used for PWHT do not allow flam e
cont act wit h t he fabricat ion as t his m ay induce large t herm al gradient s.
I t is also im port ant t o ensur e t hat t he fuel ( part icularly for oil- fired furnaces)
does not cont ain high levels of pot ent ially harm ful im purit ies – such as sulphur.
7 .5
Loca l PW H T
For a pipeline or pipe spool it is oft en necessary t o apply PWHT t o individual
welds by local applicat ion of heat .
For t his, a PWHT procedure m ust specify t he previously described param et er s
for cont rolling t he t herm al cycle but it is also necessary t o specify t he following:


Widt h of t he heat ed band ( m ust be wit hin t he soak t em perat ur e range) .
Widt h of t he t em per at ur e decay band ( soak t em perat ur e t o ~ 300°C) .
Ot her considerat ions ar e:


Posit ion of t he t herm ocouples wit hin t he heat ed band widt h and t he decay
band.
I f t he it em needs t o be support ed in a part icular way t o allow m ovem ent /
avoid dist ort ion.
The com m onest m et hod of heat ing for local PWHT is by m eans of insulat ed
elect rical elem ent s ( elect rical ‘m at s’) t hat are at t ached t o t he w eld.
Gas- fired, radiant heat ing elem ent s can also be used.
Figure 7.7 show s t ypical cont r ol zones for localised PWHT of a pipe but t weld.
WI S10- 30816
Heat Treat m ent
7- 4
Copyright © TWI Lt d
N or m a lisin g


Tem perat ure,°C

Rapid heat ing t o soak t em perat ur e ( 100% aust enit e) .
Short soak t im e at t em perat ur e.
Cool in air t o am bient t em perat ur e.
~ 900°C
Tim e
Figur e 7 .1 Typica l nor m a lising he a t t r e a t m e n t a pplie d t o C- M n a nd som e low
a lloy st e e ls.
Que nch ing a nd t e m pe r ing


Tem perat ure°C


Rapid heat ing t o soak t em perat ur e ( 100% aust enit e) .
Short soak t im e at t em perat ur e.
Rapid cooling by quenching in wat er or oil.
Reheat t o t em pering t em perat ur e, soak and air cool.
~ 900°C
> ~ 650°C
Quenching cycle
Tempering cycle
Tim e
Figur e 7 .2 Typica l que nchin g a nd t e m pe r ing he a t t r e a t m e nt a pplie d t o som e
low a lloy st e e ls.
WI S10- 30816
Heat Treat m ent
7- 5
Copyright © TWI Lt d
Slab h e a t ing temperature > ~ 1050°C
( γ)
Austenite
Tem perat ure,°C
~ 900°C
Aust enit e + ferrit e
( γ+α)
~ 700°C
Ferrit e + pearlit e
( α)฀฀+ iron carbide)
As- r olle d
or
hot r olle d
Cont r ol- r olle d
or
TM CP
Tim e
Figur e 7 .3 Com pa r ison of t he ‘cont r ol- r olle d’ ( TM CP) a nd ‘a s- r olle d’ condit ions
( = hot r olling) .
Solut ion h e a t t r e a t m e nt



Rapid heat ing t o soak t em p. ( 100% aust enit e) .
Short ‘soak’ t im e at t em perat ur e.
Rapid cool cooling by quenching int o wat er or oil.
Tem perat ure,°C
> ~ 1050°C
Que nchin g
Tim e
Figur e 7 .4 Ty pica l solut ion he a t t r e a t m e nt ( solut ion a n ne a ling) a pplie d t o
a ust e nit ic st a inle ss st e e ls.
WI S10- 30816
Heat Treat m ent
7- 6
Copyright © TWI Lt d
Ann e a ling

Rapid heat ing t o soak t em perat ur e ( 100% aust enit e) .
Short ‘soak’ t im e at t em perat ur e.
Slow cool in furnace t o am bient t em perat ur e.

Tem perat ur e,°C

~ 900°C
Tim e
Figur e 7 .5 Ty pica l a nne a ling he a t t r e a t m e nt a pplie d t o C- M n a n d som e low a lloy
st e e ls.
PW H T ( C- M n st e e ls)

Tem perat ure °C


Cont rolled heat ing rat e from 300°C t o soak t em perat ur e.
Minim um soak t im e at t em perat ur e.
Cont rolled cooling t o ~ 300°C.
~ 600°C
Controlled heating
and cooling rates
~ 300°C
Soak
time
Air cool
Tim e
Figur e 7 .6 Typica l PW H T a pplie d t o C- M n st e e ls.
WI S10- 30816
Heat Treat m ent
7- 7
Copyright © TWI Lt d
Weld seam
Figur e 7 .7 Loca l PW H T of a pipe gir t h se a m .
WI S10- 30816
Heat Treat m ent
7- 8
Copyright © TWI Lt d
Heat Treatment
Controlled heating and cooling to bring about
desired changes in metals and alloys
Objectives
 Microstructural changes improve mechanical
properties ie toughness, machinability,
strength.
 Reduce residual stress level.
Heat Treatment
Section 7
Where?
Global
Local
Copyright © TWI Ltd
Copyright © TWI Ltd
Carrying Out Heat Treatment
Heat Treatment Equipment
Furnaces and ovens
Heating & cooling
bulk specimen
Furnaces and
ovens
Gas fired
Electric
Heat
Treatment
Electric heating
mats
Temperature
control? Use
thermocouples,
optical
pyrometers
Localised Heat
treatment
Localised heat
sources
Flame heating
Induction heating
Laser heating
Gas fired:
 Special attention to environment control.
 Heat from oxygen + fuel gas (methane, propane).
 High concentration of oxygen may result in scaling,
a neutral environment is beneficial.
 Avoid heat gradients.
 Radiant tube furnaces to avoid contact with
combustion product.
Electric furnaces:
 Cleaner environment.
 Expensive.
Copyright © TWI Ltd
Copyright © TWI Ltd
Localised Heat Treatment
 Heating and cooling a specific portion of a
component, ie gear edge, case or surface
hardening, weld PWHT.
 Gas flames such as oxygen + methane or
propane.
 Induction.
 Electric heating blankets.
Heat Treatment Cycle
Temperature
Soaking temperature
Important
parameters
 Heating rate.
 Soaking
temperature.
 Soaking time
(1h/25mm).
 Cooling rate.
Time
Heating
Copyright © TWI Ltd
Soaking
Cooling
Copyright © TWI Ltd
7‐1
Types of Heat Treatment
 Annealing.
 Normalising.
 Recovery and
re-crystallisation.
 Stress relief.
 Quenching and tempering.
 Precipitation hardening.
Heat Treatment Temperatures
oC
Homogenizing and hot working
Welds & parent
metals
Austenite
Acm
910
Annealing
Normalizing
A3
Normalising
Annealing
727
Recovery and recrystallization
Parent metals
Recovery & recrystallisation
Stress relief &
PWHT
A1
600
PWHT and PWHT
Stress Relieve
Phase change
to austenite
No phase
change
500
0.022
0.77
2.0
Carbon content in weight %
Copyright © TWI Ltd
Copyright © TWI Ltd
Full Annealing - Steel
 Heated to high temperature (Partially or fully
austenitic):
□





Hypereutectic steels are partially austenitized to
avoid cementite formation on grain boundaries
during slow cooling.
Hold for some time and then slow cool.
Coarse grain size.
Reduced strength.
Increased ductility.
Homogeneous.
Pearlite
Normalising






Steel heated just to where austenite is stable.
Air cooling – fairly rapid.
Grain refinement.
Pearlite
Stress relief.
Higher strength.
Higher toughness.
Ferrite
Ferrite
Copyright © TWI Ltd
Recovery and Re-crystallisation
 Cold work increases strength and reduces
ductility and toughness.
 Reversed by recovery and re-crystallisation:
□
Copyright © TWI Ltd
Recovery and Recrystallisation
Heat treatment temperature (o F)
But if temperature too high excessive grain
growth leads to drop in strength and toughness.
 Recovery reduces the stored energy in coldworked or deformed (rolled) material.
 Dislocations move and align at heat treatment
temperature (recovery).
 New defect-free grains nucleate from grain
boundaries and grow (recrystallisation).
Heat treatment temperature (o C)
Copyright © TWI Ltd
Copyright © TWI Ltd
7‐2
Non Equilibrium Heat
Treatment - Quenching
Non Equilibrium Heat
Treatment - Quenching
 Heating to annealing heat treatment
temperature range.
 Fast cooling to increase hardness:
oC
Austenite
□
Acm
910
□
A3
Annealing
□
A1
0.83
0.05
Increased quench severity
 Ductility and toughness are drastically
reduced.
 Usually followed by tempering.
727
2.0
Carbon content in weight %
Copyright © TWI Ltd
Copyright © TWI Ltd
Tempering
Tempering
 Subcritical (Below A1) Heat treatment to tailor
hardness/strength of martensite.
 Performed after quenching to reduce the
brittleness.
 Ductility and toughness are improved.
 Removes stresses due to quenching.
Hardness
0.008
Brine (Water and salt).
Water.
Oil.
As- 100
quenched
200
300
400
500
600
700
o
Low C steel (0.12C)
Annealed at 900°C for 30
minutes and water quenched.
380Hv
C
After tempering at 700°C for 30
minutes and air cooled.
245Hv
Copyright © TWI Ltd
Copyright © TWI Ltd
Heat Treatments Following Welding
Stress relief
 Carried out at lower temperature, to reduce
residual stresses.
Stress Relief and PWHT
oC
Austenite
910
Tempering
 Carried out at higher temperature (for
constructional steels).
 Not only relieves stresses but also softens the
hard HAZ microstructure.
A3
A1
727
Tempering
600
500
Stress Relief
0.022
0.77
Carbon content
in weight %
Copyright © TWI Ltd
Acm
2.0
 No phase
transformation.
 Slow heating and
cooling (max: 50°C/h).
 Soaking time
1hr/25mm of thickest
section.
 Usual temperature for
PWHT (C-Mn steel) –
550 to 650°C.
 Stress Relief carried
out after cold work or
welding, at lower
temperatures.
Copyright © TWI Ltd
7‐3
PWHT Effect on Residual Stress
YS at room
temperature
Soaking
temperature
PWHT Effects
PWHT
temperature
Residual
stress level
YS at soaking
temperature
Actual
YS
Time
Copyright © TWI Ltd
PWHT Recommendations
 Provide adequate support (low YS at high
temperature!).
 Control heating rate to avoid uneven thermal
expansions.
 Control soak time to equalise temperatures.
 Control temperature gradients - No direct
flame impingement.
 Control furnace atmosphere to reduce scaling.
 Control cooling rate to avoid new residual
stresses.
 For specific PWHT applications see standards,
eg ASME VIII, ASME B31.3, ASME B31.8.
Copyright © TWI Ltd
Question 1
While inspecting some cast duplex valve bodies
one of your inspectors asks if the castings
require a heat treatment process. Which of the
following would most likely be applied to these
items?
a.
b.
c.
d.
Solution annealing
Quench hardening
No heat treatment required
Stress relieving would be required but only
after welding if applicable
Copyright © TWI Ltd
Copyright © TWI Ltd
Heat Treatments
You are assigned to a heat treatment company
to witness heat treatments being conducted.
The heat treatments are being conducted on
various products for a major offshore oil and gas
project that you have been involved with.
Copyright © TWI Ltd
Question 2
A set of fabricated brackets manufactured from
316L stainless steel is about to be heat-treated,
which of the following applies?
a. This material is always stressed relieved after
welding
b. A post weld heat treat isn’t generally
conducted on this type of material
c. Quench hardening would always be applied to
this material to increase toughness after
welding
d. All options are incorrect
Copyright © TWI Ltd
7‐4
Question 3
During the post weld heat treatment of a small
welded fabrication, you observe the heat treatment
personnel applying heat by a heating torch. In
accordance with TWI Specification do you consider
this an acceptable practice?
a. Yes this is acceptable providing the temperature
attained and the soaking times are correct in
accordance with the approved PWHT procedure
b. Yes this is acceptable providing the
thermocouples are correctly placed and
calibrated
c. No, this application method isn’t acceptable
d. 2 options are correct
Copyright © TWI Ltd
Question 5
It is a requirement for a quenched and tempered
component to undergo post weld heat treatment, one
of your inspectors asks you what is the maximum
temperature required for this material. Which of the
following is correct in accordance the TWI
Specification?
a. The same as for C/Mn steel
b. You would never permit a PWHT to be carried out
on this material
c. The TWI Specification doesn’t reference this
information, but would expect it to be around
680°C
d. All options are incorrect
Copyright © TWI Ltd
Question 7
After a PWHT process has been carried out on
some thick to thin C/Mn pipe spools (12.5mm to
25mm WT) you notice that the heating rate is
recorded at 200°C/Hr. In accordance with the
TWI Specification is this correct?
a.
b.
c.
d.
No, it should be a minimum of 220°C/hr
No, it should be 40°C/hr
Yes, Providing the cooling rate is the same
Yes, providing the cooling rate is 220°C/hr
Copyright © TWI Ltd
Question 4
Unfortunately the stress relieving of a welded fabricated
steel structure hasn’t been witnessed by any of your
inspectors. When you review the PWHT chart you notice
only 2 thermocouples have been used. In accordance with
the TWI Specification do you consider this to be acceptable?
a. No, all PWHT shall be witnessed and a minimum of 3
thermocouples shall be used
b. Yes, only the PWHT charts require reviewing by
inspectors
c. No, all PWHT shall be witnessed, an inspector has to be
present 100% of the time throughout the PWHT process
d. No, a minimum of 3 thermocouples shall be used, and
calibration certificates require checking prior to the heat
treatment process
Copyright © TWI Ltd
Question 6
During Post Weld Heat Treatment, what
sequence of events occurs to the properties of
the material?
a. Yield strength increases, stresses decrease
then yield strength decreases
b. Ductility decreases, stresses increase then
ductility increases
c. Yield strength decreases, stresses decrease
then yield strength increases
d. Stresses increase, stresses decrease then
yield increases
Copyright © TWI Ltd
Question 8
While reviewing the heat treatment chart for a PWHT
process you notice that the temperature is not
recorded below 150°C on the cooling cycle. Would
you accept this chart?
a. No, the temperature must be recorded down to
room temperature
b. It would depend on the thickness and grade of
material as to whether this would be acceptable
or not
c. No, the temperature has to be recorded to at
least 110°C
d. The TWI Specification doesn’t reference this
information.
Copyright © TWI Ltd
7‐5
Question 9
In certain cases heat treatments are conducted
on cold work components such as cold rolled,
steel plate. Which of the following heat
treatments would you expect to be conducted on
these components?
a.
b.
c.
d.
Stress relieving
Densensitization
Quench hardening
Post hydrogen release
Copyright © TWI Ltd
Question 10
You notice from your records you don’t have an
inspection report for a component that has undergone
a PWHT. In this case what would your course of action
be?
a. It would be acceptable, If the component had a full
inspection report before PWHT
b. The TWI Specification makes no reference of this,
so you would have to seek advice
c. It is a requirement that all components undergo
full inspection after a PWHT process has been
conducted; in this case it would not be acceptable
d. As long as no welding has be conducted after the
PWHT process, this would be acceptable
Copyright © TWI Ltd
7‐6
Se ct ion 8
W PS a n d W e lde r Qu a lifica t ion s
8
W PS a n d W e lde r Qu a lifica t ion s
When st ruct ures and pr essurised it em s ar e fabricat ed by w elding, it is essent ial
t hat all t he welded j oint s are sound and have suit able propert ies for t heir
applicat ion.
Cont rol of w elding is by m eans of w elding procedur e specificat ions ( WPS) t hat
give det ailed writ t en inst ruct ions about t he welding condit ions t hat m ust be
used t o ensur e t hat welded j oint s have t he r equired propert ies.
Alt hough WPS are shop floor docum ent s t o inst ruct w elders, welding inspect or s
need t o be fam iliar wit h t hem because t hey will need t o refer t o WPSs when
t hey ar e checking t hat welders ar e w orking in accordance wit h t he specified
requirem ent s.
Welders need t o underst and WPSs and have t he skill t o m ak e w elds t hat ar e not
defect ive and dem onst rat e t hese abilit ies befor e being allowed t o m ake
product ion welds.
8 .1
Qua lif ie d w e ldin g pr oce dur e spe cif ica t ion s
I t is indust ry pract ice t o use qu a lifie d W PS for m ost applicat ions.
A welding procedur e is usu a lly qu a lif ie d by m aking a t est w eld t o dem onst rat e
t hat t he pr opert ies of t he j oint sat isfy t he r equirem ent s specified by t he
applicat ion st andard ( and t he client / end user) .
Dem onst rat ing t he m echanical propert ies of t he j oint is t he principal purpose of
qualificat ion t est s but showing t hat a defect - fr ee weld can be produced is also
very im port ant .
Product ion welds t hat are m ade in accordance wit h welding condit ions sim ilar t o
t hose used for a t est weld should have sim ilar propert ies and t her efor e be fit for
t heir int ended purpose.
Figure 8.1 is an exam ple of a t ypical WPS writ t en in accordance wit h t he
Eur opean Welding St andard form at giving det ails of all t he welding condit ions
t hat need t o be specified.
8 .1 .1
W e ld ing st a nd a r ds for p r oce d ur e q ua lifica t ion
Eur opean and Am erican St andards hav e been dev eloped t o give com pr ehensive
det ails about :




How a w elded t est piece m ust be m ade t o dem onst rat e j oint propert ies.
How t he t est piece m ust be t est ed.
What welding det ails need t o be included in a WPS?
The range of pr oduct ion welding allowed by a part icular qualificat ion t est
weld.
WI S10- 30816
WPS and Welder Qualificat ions
8- 1
Copyright © TWI Lt d
The principal Eur ope a n St a nda r ds t hat specify t hese r equirem ent s ar e:
BS EN I SO 1 5 6 1 4 Specificat ion and qualificat ion of welding procedures for
m et allic m at erials – Welding procedur e t est .
Pa r t 1 : Arc & gas w elding of st eels & arc welding of nickel & nickel alloys.
Pa r t 2 : Arc w elding of alum inium and it s alloys.
The principal Am e r ica n St a nd a r d s for pr ocedure qualificat ion are:
ASM E Se ct ion I X for pressurised sy st em s ( v essels & pipewor k) .
AW S D 1 .1 St ruct ural welding of st eels.
AW S D 1 .2 St ruct ural welding of alum inium .
8 .1 .2
The qua lif ica t ion pr oce ss for w e lding pr oce dur e s
Alt hough qualified WPS are usually based on t est welds t hat have been m ade t o
dem onst rat e weld j oint propert ies; welding st andards also allow qualified WPS
t o be writ t en based on ot her dat a ( for som e applicat ions) .
Som e alt ernat ive ways t hat can be used for writ ing qualified WPS for som e
applicat ions are:


Qua lif ica t ion by a dopt ion of a st a nda r d w e ldin g pr oce dur e - t est
welds previously qualified and docum ent ed by ot her m anufact ur er s.
Qua lif ica t ion ba se d on pr e v iou s w e lding e x pe r ie nce - w eld j oint s t hat
have been r epeat edly m ade and proved t o have suit able propert ies by t heir
service record.
Procedure qualificat ion t o Eur opean St andards by m eans of a t est w eld ( and
sim ilar in ASME Sect ion I X and AWS) requires a sequence of act ions t hat is
t ypified by t hose shown by Table 8.1.
A successful procedure qualificat ion t est is com plet ed by t he product ion of a
welding procedur e qualificat ion record ( WPQR) , an exam ple of which is shown
by Figure 8.2.
8 .1 .3
Re la t ionship be t w e e n a W PQR a n d a W PS
Once a WPQR has been produced, t he welding engineer is able t o writ e
qua lif ie d W PSs for t he various product ion weld j oint s t hat need t o be m ade.
The welding condit ions t hat are allowed t o be writ t en on a qualified WPS are
referr ed t o as t he qu a lifica t ion r a nge and t his range depends on t he welding
condit ions t hat wer e used for t he t est piece ( t he as- run det ails) and form part
of t he WPQR.
Welding condit ions are referr ed t o as w e lding va r ia ble s by Eur opean and
Am erican Welding St andards and ar e classified as eit her e sse nt ia l va r ia ble s or
non- e sse nt ia l v a r ia ble s.
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These variables can be defined as follows:


Esse nt ia l va r ia ble a variable t hat has an effect on t he m echanical
propert ies of t he w eldm ent ( and if changed beyond t he lim it s specified by
t he st andard will require t he WPS t o be re- qualified) .
N on- e sse nt ia l v a r ia ble a variable t hat m ust be specified on a WPS but
does not hav e a significant effect on t he m echanical propert ies of t he
weldm ent ( and can be changed w it h ou t n e e d for r e - qua lifica t ion but will
require a new WPS t o be w rit t en) .
I t is because essent ial variables can have a significant effect on m echanical
propert ies t hat t hey ar e t he cont r olling variables t hat govern t he qualificat ion
range and det erm ine w hat can be writ t en int o a WPS.
I f a w elder m ak es a pr oduct ion weld using condit ions out side t he qualificat ion
range given on a part icular WPS, t here is danger t hat t he w elded j oint will not
have t he r equired pr opert ies and t her e ar e t hen t wo opt ions:


Make anot her t est w eld using sim ilar welding condit ions t o t hose used for
t he affect ed weld and subj ect t his t o t he sam e t est s used for t he r elevant
WPQR t o dem onst rat e t hat t he propert ies st ill sat isfy specified
requirem ent s.
Rem ove t he affect ed w eld and re- weld t he j oint st rict ly in accordance wit h
t he designat ed WPS.
Most of t he w elding variables t hat are classed as essent ial are t he sam e in bot h
t he European and Am erican Welding St andards but t heir qualificat ion ranges
m ay differ .
Som e Applicat ion St andards specify t heir own essent ial variables and it is
necessary t o ensur e t hat t hese ar e t aken int o considerat ion when procedur es
are qualified and WPSs are writ t en.
Exam ples of essent ial variables ( according t o European Welding St andards) ar e
given in Table 8.2.
8 .2
W e lde r qu a lifica t ion
The use of qualified WPSs is t he accept ed m et hod for cont rolling product ion
welding but t his will only be successful if t he welder s have t he abilit y t o
underst and and w or k in accordance wit h t hem .
Welders also need t o have t he skill t o consist ent ly produce sound welds ( free
from defect s) .
Welding St andards have been dev eloped t o give guidance on what part icular
t est welds are r equired in order t o show t hat welders have t he r equired skills t o
m ake part icular t ypes of product ion w elds in part icular m at erials.
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8.2.1
Welding standards for welder qualification
The principal European Standards that specify requirements are:
EN 287-1 /
BS EN ISO 9606
Qualification test of welders – Fusion welding
Part 1: Steels
BS EN ISO 9606-2 Qualification test of welders – Fusion welding
Part 2: Aluminium and aluminium alloys
BS EN ISO 14732
Welding personnel. Qualification testing of welding
operators and weld setters for mechanized and automatic
welding of metallic materials
The principal American Standards that specify requirements for welder
qualification are:
8.2.2
ASME Section IX
Pressurised systems (vessels & pipework)
AWS D1.1
Structural welding of steels
AWS D1.2
Structural welding of aluminium
The qualification process for welders
Qualification testing of welders to European Standards requires test welds to be
made and subjected to specified tests to demonstrate that the welder
understands the WPS and can produce a sound weld.
For manual and semi-automatic welding the emphasis of the tests is to
demonstrate ability to manipulate the electrode or welding torch.
For mechanised and automatic welding the emphasis is on demonstrating that
welding operators have ability to control particular types of welding equipment.
American Standards allow welders to demonstrate that they can produce sound
welds by subjecting their first production weld to non-destructive testing.
Table 8.3 shows the steps required for qualifying welders in accordance with
European Standards.
Figure 8.5 shows a typical Welder Qualification Certificate in accordance with
European Standards.
8.2.3
Welder qualification and production welding allowed
The welder is allowed to make production welds within the range of qualification
recorded on his welder qualification certificate.
The range of qualification is based on the limits specified by the Welding
Standard for welder qualification essential variables - defined as: a
variable that if changed beyond the limits specified by the Welding Standard
may require greater skill than has been demonstrated by the test weld.
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Som e w elding variables t hat ar e classed as essent ial for welder qualificat ion are
t he sa m e t ype s as t hose classified as essent ial for w elding procedur e
qualificat ion, but t he range of qualificat ion m ay be significant ly wider.
Som e essent ial variables ar e specific t o welder qualificat ion.
Exam ples of welder qualificat ion essent ial variables are given in Table 8.4.
8 .2 .4
Pe r iod of v a lidit y for a w e lde r qua lifica t ion ce r t ifica t e
A welder ’s qualificat ion begins from t he dat e of welding of t he t est piece.
The Eur opean St andard allows a qualificat ion cert ificat e t o r em ain valid for a
period of t w o y ear s – pr ovided t hat :


8 .2 .5
The w elding co- ordinat or, or ot her r esponsible per son, can confirm t hat t he
w e lde r h a s be e n w or k ing w it hin t he in it ia l r a nge of qua lif ica t ion.
Working wit hin t he init ial qualificat ion range is confirm ed ev ery six m ont hs.
Pr olonga t ion of w e lde r qu a lifica t ion
A welder’s qualificat ion cert ificat e can be pr olonged every t w o y ear s by an
exam iner/ exam ining body but befor e pr olongat ion is allowed cert ain condit ions
need t o be sat isfied:



Records/ evidence ar e available t hat can be t r aced t o t he w elder and t he
WPS t hat have been used for pr oduct ion welding.
The support ing evidence m ust r elat e t o volum et ric exam inat ion of t he
welder’s product ion w elds ( RT or UT) on t w o w elds m ade during t he 6
m ont hs prior t o t he pr olongat ion dat e.
The support ing evidence w elds m ust sat isfy t he accept ance lev els for
im perfect ions specified by t he Eur opean w elding st andard and have been
m ade under t he sam e condit ions as t he original t est weld.
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Ta ble 8 .1 Typica l se que nce for w e lding pr oce dur e qua lifica t ion by m e a ns of a
t e st w e ld.
Th e w e ldin g e n gin e e r w r it e s a pr e lim ina r y W e lding Pr oce dur e
Spe cifica t ion ( pW PS) for e a ch t e st coupon t o be w e lde d


A welder m ak es t he t est coupon in accordance wit h t he pWPS
A welding inspect or r ecords all t he welding condit ions used t o m ake
t he t est coupon ( called t he as- run condit ions)
An I ndependent Exam iner/ Exam ining Body/ Third Part y I nspect or m a y be
request ed t o m onit or t he pr ocedur e qualificat ion
The t e st coupon is su bj e ct e d t o N D T in a ccor da nce w it h t he
m e t hods spe cif ie d by t he St a n da r d – visua l inspe ct ion, M T or PT
a nd RT or UT



The t est coupon is dest r uct ively t est ed ( t ensile, bend, m acr o t est s)
The code/ applicat ion st andard/ client m ay require addit ional t est s such
as hardness t est s, im pact t est s or corr osion t est s – depending on
m at erial and applicat ion
A Welding Procedur e Qualificat ion Record ( WPQR) is prepared by t he
welding engineer giving det ails of:
»
»
»
»

The a s- r un w e ldin g condit ion s
Re su lt s of t he N D T
Re su lt s of t he de st r u ct ive t e st s
The w e lding condit ions a llow e d for pr oduct ion w e lding
I f a Third Part y I nspect or is involved he will be request ed t o sign t he
WPQR as a t rue r ecord of t he t est
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Ta ble 8 .2 Typica l e x a m ple s of W PS e sse nt ia l va r ia ble s a ccor ding t o Eur ope a n
W e lding St a nda r ds.
VARI ABLE
RAN GE for PROCED URE QUALI FI CATI ON
W e lding pr oce ss
No range – pr ocess qualified is process t hat m ust be
used in product ion
PW H T
Joint s t est ed aft er PWHT only qualify as PWHT
product ion j oint s
Joint s t est ed ‘as- welded’ only qualify ‘as- welded’
product ion j oint s
Pa r e nt
t ype
m a t e r ia l
Par ent m at erials of sim ilar com posit ion and m echanical
propert ies ar e allocat ed t he sam e Mat erial Group No.;
qualificat ion only allows product ion welding of m at erials
wit h t he sam e Gr oup No.
W e lding
consu m a ble s
Consum ables for pr oduct ion welding m ust have t he
sam e Eur opean designat ion – as a general rule
M a t e r ia l
t hick ne ss
A t hickness range is allowed – below and abov e t he t est
coupon t hickness
Type of cu r r e n t
AC only qualifies for AC; DC polarit y ( + VE or - VE)
cannot be changed; pulsed current only qualifies for
pulsed curr ent pr oduct ion welding
Pr e h e a t
t e m pe r a t ur e
The pr eheat t em perat ure used for t he t est is t he
m inim um t hat m ust be applied
I nt e r pa ss
t e m pe r a t ur e
The highest int erpass t em perat ur e reached in t he t est is
t he m axim um allowed
H e a t input ( H I )
When im pact requirem ent s apply m axim um HI allowed
is 25% abov e t est HI
when hardness r equirem ent s apply m inim um HI allowed
is 25% below t est HI
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Ta ble 8 .3 St a ge s for qu a lifica t ion of a w e lde r .
Th e w e ldin g e ngin e e r w r it e s a
W PS for w e lde r qua lif ica t ion t e st pie ce

The w e lde r m a k e s t h e t e st w e ld in a ccor da nce w it h t h e W PS
A w e ldin g in spe ct or m on it or s t h e w e ldin g t o e nsu r e t h a t t h e w e lde r
is w or k in g in a ccor da nce t he W PS
An I ndependent Exam iner/ Exam ining Body/ Thir d Part y I nspect or m a y be
request ed t o m onit or t he t est




The t e st cou pon is subj e ct e d t o N D T in a ccor da nce w it h t h e
m e t hods spe cifie d by t he St a n da r d ( v isu a l in spe ct ion, M T or PT
a nd RT or UT)
For ce r t a in m a t e r ia ls, a nd w e lding pr oce sse s, som e de st r uct iv e
t e st ing m a y be r e qu ir e d ( be n ds or m a cr os)
A W e lde r ’s Qua lif ica t ion Ce r t if ica t e is pr e pa r e d sh ow ing t he
w e ldin g con dit ion s u se d for t h e t e st pie ce a n d t h e r a n ge of
qua lif ica t ion a llow e d by t h e St a n da r d for pr oduct ion w e ldin g
I f a Thir d Pa r t y is in volve d, t h e Qu a lifica t ion Ce r t ifica t e w ould
be e ndor se d a s a t r ue r e cor d of t he t e st
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Ta ble 8 .4 Typica l e x a m ple s of w e lde r qua lifica t ion e sse nt ia l va r ia ble s a ccor ding
t o Eur ope a n W e lding St a nda r ds.
VARI ABLE
RAN GE for W ELD ER QUALI FI CATI ON
W elding proce ss
No range – pr ocess qualified is process t hat a welder
can use in product ion
Type of w eld
But t welds cover any t y pe of j oint except branch welds
fillet welds only qualify fillet s
Pa re nt
t ype
Par ent m at erials of sim ilar com posit ion and m echanical
propert ies ar e allocat ed t he sam e Mat erial Group No.;
qualificat ion only allows product ion w elding of m at erials
wit h t he sam e Group No. but t he Groups allow m uch
wider com posit ion ranges t han t he pr ocedur e Groups
m at e ria l
Filler m at er ia l
Elect r odes and filler wires for product ion welding m ust
be of t he sam e form as t he t est ( solid wire, flux cor ed,
et c) ; for MMA coat ing t ype is essent ial. The filler wire
m ust fall wit hin t he range of t he qualificat ion of t he filler
m at erial.
M at er ial
t hick ness
A t hickness range is allowed; for t est pieces abov e
12m m allow  5m m
Pipe dia m et e r
Essent ial and very rest rict ed for sm all diam et er s; t est
pieces above 25m m allow  0.5 x diam et er used ( m in.
25m m )
W elding posit ions
Posit ion of welding very im port ant ; H- L045 allows all
posit ions ( except PG)
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Figur e 8 .1 Ex a m ple of a w e lding pr oce dur e spe cifica t ion ( W PS) t o EN 1 5 6 1 4
for m a t .
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Figur e 8 .2 Ex a m ple of a W PQR docum e nt ( qu a lifica t ion r a nge ) t o EN 1 5 6 1 4
for m a t .
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Figur e 8 .3 Ex a m ple of W PQR docum e nt ( t e st w e ld de t a ils) t o EN 1 5 6 1 4 for m a t .
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Figur e 8 .4 Ex a m ple of a W PQR docum e nt ( de t a ils of w e ld t e st ) t o EN 1 5 6 1 4
for m a t .
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Figur e 8 .5 Ex a m ple of a w e lde r qua lifica t ion t e st ce r t ifica t e ( W PQ) t o EN 2 8 7
for m a t .
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WPS and Welder Qualificat ions
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Welding Procedure Qualification
Question:
What is the main reason for carrying out a Welding
Procedure Qualification Test?
(What is the test trying to show?)
Welding Procedure and Welder Qualification
Answer:
To show that the welded joint has the properties*
that satisfy the design requirements (fit for purpose).
Section 8
* Properties
 Mechanical properties are the main interest - always
strength but toughness & hardness may be important
for some applications.
 Test also demonstrates that the weld can be made
without defects.
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Welding Procedures
Purpose of a WPS
 To achieve specific properties.






□ Mechanical strength, corrosion resistance,
composition.
To ensure freedom from defects.
To enforce QC procedures.
To standardise on methods and costs.
To control production schedules.
To form a record.
Application standard or contract requirement.
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Welding Procedure Qualification
(according to BS EN ISO 15614)
Preliminary Welding Procedure Specification (pWPS)
Welding Procedure Qualification Record (WPQR)
Welding Procedure Specification (WPS)
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Welding Procedures
Object of a welding procedure test
 To give maximum confidence that the welds
mechanical and metallurgical properties meet
the requirements of the applicable
code/specification.
 Each welding procedure will show a range to
which the procedure is approved (extent of
approval).
 If a customer queries the approval evidence
can be supplied to prove its validity.
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Welding Procedures
Producing a welding procedure involves
 Planning the tasks.
 Collecting the data.
 Writing a procedure for use of for trial.
 Making a test welds.
 Evaluating the results.
 Approving the procedure.
 Preparing the documentation.
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8‐1
Welding Procedure Qualification
Preliminary Welding Procedure Specification
(pWPS)
Welding Engineer writes a preliminary Welding
Procedure Specification (pWPS) for each test weld
to be made.
Welding Procedure Qualification
Welding Procedure Qualification Record (WPQR)
 A welder makes a test weld in accordance with the
pWPS.
 A welding inspector records all the welding conditions
used for the test weld (referred to as the 'as-run'
conditions).
An Independent Examiner/ Examining Body/ Third Party
inspector may be requested to monitor the
qualification process.
The finished test weld is subjected to NDT in
accordance with the methods specified by the EN ISO
Standard - Visual, MT or PT & RT or UT.
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Welding Procedure Qualification
Welding Procedure Qualification Record (WPQR)
 Test weld is subjected to destructive testing (tensile,
bend, macro).
 The Application Standard, or Client, may require
additional tests such as impact tests, hardness tests
(and for some materials - corrosion tests).
Welding Procedure Qualification Record (WPQR)
 The welding conditions used for the test weld

Results of the NDT.

Results of the destructive tests.

The welding conditions that the test weld allows for
production welding.
 The Third Party may be requested to sign the WPQR as
a true record.
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Welding Procedure Qualification
Welding Procedure Specification (WPS)
 The welding engineer writes qualified
Welding Procedure Specifications (WPS) for
production welding.
 Production welding conditions must remain
within the range of qualification allowed by
the WPQR.
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Welding Procedure Qualification
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Welding Procedure Qualification
(according to EN Standards)
Welding conditions are called welding variables.
(according to EN Standards)
Welding essential variables
Welding variables are classified by the EN ISO Standard as:
Question:
Why are some welding variables classified as
essential?
 Essential variables.
 Non-essential variables.
 Additional variables.
Note: Additional variables = ASME supplementary essential.
The range of qualification for production welding is based
on the limits that the EN ISO Standard specifies for essential
variables*
Answer:
A variable, that if changed beyond certain limits
(specified by the Welding Standard) may have a
significant effect on the properties* of the
joint.
* particularly joint strength and ductility.
(* and when applicable - the additional variables)
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8‐2
Welding Procedure Qualification
(according to EN Standards)
Welding additional variables
Question:
Why are some welding variables classified as
additional?
Answer:
A variable, that if changed beyond certain limits
(specified by the Welding Standard) may have a
significant effect on the toughness and/or
hardness of the joint.
Note: ASME calls variables that affect toughness as
supplementary essential variables (but does not refer to
hardness).
Welding Procedure Qualification
(according to EN Standards)
Some typical essential variables
 Welding process.
 Post weld heat treatment (PWHT).
 Material type.
 Electrode type, filler wire type (Classification).
 Material thickness.
 Polarity (AC, DC+ve/DC-ve).
 Pre-heat temperature.
Some typical additional variables
 Heat input.
 Welding position.
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Welding Procedures
In most codes reference is made to how the procedure are
to be devised and whether approval of these procedures is
required.
Welding Procedures
Components of a welding procedure
Parent material
 Type (Grouping).
 Thickness.
 Diameter (Pipes).
 Surface condition.
The approach used for procedure approval depends on the
code.
Example codes
 AWS D.1.1: Structural Steel Welding Code.
 BS 2633: Class 1 welding of Steel Pipe Work.
 API 1104: Welding of Pipelines.
 BS 4515: Welding of Pipelines over 7 Bar.
Welding process
 Type of process (MMA, MAG, TIG, SAW etc).
 Equipment parameters.
 Amps, volts, travel speed.
Other codes may not specifically deal with the requirement
of a procedure but may contain information that may be
used in writing a weld procedure.
 EN 1011: Process of Arc Welding Steels.
Welding consumables
 Type of consumable/diameter of consumable.
 Brand/classification.
 Heat treatments/storage.
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Welding Procedures
Components of a welding procedure
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Welding Procedures
Example
Welding
Procedure
Specification
(WPS)
Joint design
 Edge preparation.
 Root gap, root face.
 Jigging and tacking.
 Type of backing
Welding position
 Location, shop or site.
 Welding position e.g. PA, PB, PC etc.
 Any weather precaution.
Thermal heat treatments
 Preheat, temps.
 Post weld heat treatments eg stress relieving.
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8‐3
Welding Positions
PA
1G / 1F
Flat / Downhand
Horizontal-Vertical
PB
2F
PC
2G
Horizontal
PD
4F
Horizontal-Vertical (Overhead)
PE
4G
Overhead
PF
3G / 5G
Vertical-Up
PG
3G / 5G
Vertical-Down
H-L045
6G
Inclined Pipe (Upwards)
J-L045
6G
Inclined Pipe (Downwards)
Welding Positions
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Welding Procedures
Monitoring heat input
As Required by BS EN ISO 15614-1:2004
In accordance with BS EN 1011-1:1998
Welding Procedures
15614-1-2-3
 When impact requirements apply, the upper limit of
heat input qualified is 25% greater than that used in
welding the test piece.
 When hardness requirements apply, the lower limit of
heat input qualified is 25% lower than that used in
welding the test piece.
 Heat input is calculated in accordance with BS EN10111.
 If welding procedure tests have been preformed at both
a high and low heat input level, then all intermediate
heat inputs are also qualified.
Specifies contents of WPS
"Shall give details of how a welding operation is
to be performed and contain all relevant
information".
Definitions
 Processes to be designated in accordance with
BS EN ISO 4063.
 Welding positions in accordance with BS EN ISO
6947.
 Typical WPS form.
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Welding Procedures
BS EN ISO 15614-1:2004 (Replaced BS EN 288-3)
"does not invalidate previous … approvals made to
former national standards… providing the intent of the
technical requirements is satisfied… approvals are
relevant"
"where additional tests… make the approval technically
equivalent… only necessary to do the additional tests…"
"approval is valid… in workshops or sites under the
same technical and quality control of that
manufacturer…"
"service, material or manufacturing conditions may
require more comprehensive testing… "
Application standard may require more testing
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Welding Procedures
Table 5
Thickness of
test piece
t
BS EN ISO 15614-1:2004
Range of qualification
Single run
Multi run
t<3
0.7t to 1.3ta
0.7t to 2t
3<t<12
0.5t (3 min) to 1.3ta
3 to 2ta
12<t<100
0.5t to 1.1t
0.5t to 2t
t>100
Not applicable
50 to 2t
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Welding Procedures
Table 6
BS EN ISO 15614-1:2004 (Replaced BS EN 288-3)
Covers Arc & Gas Welding of Steels &
Arc Welding of Nickel & Nickel Alloys
BS EN ISO 15614-1:2004
Range of qualification
Thickness of
test piece
t
Material
Thickness
t<3
Welding Procedures
Throat Thickness
Single run
Multi run
0.7 to 2 t
0.75 a to
1.5 a
No
restriction
3<t<30
0.5t (3 min)
to 1.2 t
0.75 a to
1.5 a
No
restriction
t>30
>5
a
No
restriction
111
12
135
137
15
-
MMA
SAW
MAG
FCAW - inert gas
PLASMA ARC
114
131
136
141
311
- FCAW - no gas shield
- MIG
- FCAW - active gas
- TIG
– Oxy-Acetylene
The principle of this European Standard may be applied to
other fusion welding processes
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Welding Procedures
Welding Procedures
TABLE 7
Note 1:
a is the throat as used for the test piece.
Note 2:
Where the fillet weld is qualified by means of a
butt test, the throat thickness range qualified
shall be based on the thickness of the deposited
metal.
For special applications only. Each fillet weld
shall be proofed separately by a welding
procedure test.
BS EN ISO 15614-1:2004
Diameter of the test
piece Da, mm
Range of Qualification
D<25
0.5 D to 2 D
D>25
>0.5 D (25 mm min)
Note: For structural hollow sections D is the dimension of
the smaller side
a
D is the outside diameter of the pipe or outside
diameter of the branch pipe
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CSWIP 3.2 Welding Inspection
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Welder Qualification
(according to BS EN Standards)
Question:
What is the main reason for qualifying a welder?
Welder Approval
Answer:
To show that he has the skill to be able to make
production welds that are free from defects.
Note: When welding in accordance with a
Qualified WPS.
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8‐5
Welder Qualification
(according to BS EN ISO 9606)
An approved WPS should be available covering the
range of qualification required for the welder
approval.
 The welder qualifies in accordance with an
approved WPS.
 A welding inspector monitors the welding to make
sure that the welder uses the conditions specified
by the WPS.
EN Welding Standard states that an Independent
Examiner, Examining Body or Third Party Inspector
may be required to monitor the qualification process.
Welder Qualification
(according to BS EN ISO 9606)
The finished test weld is subjected to NDT by the methods
specified by the EN Standard - Visual, MT or PT & RT or UT.
The test weld may need to be destructively tested - for
certain materials and/or welding processes specified by the
EN Standard or the Client Specification.
 A Welder’s Qualification Certificate is prepared showing
the conditions used for the test weld and the range of
qualification allowed by the EN Standard for production
welding.
 The Qualification Certificate is usually endorsed by a
Third Party Inspector as a true record of the test.
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Welder Qualification
(according to BS EN ISO 9606)
The welder is allowed to make production welds within the
range of qualification shown on the Certificate.
The range of qualification allowed for production welding is
based on the limits that the EN Standard specifies for the
welder qualification essential variables.
A Welder’s Qualification Certificate automatically expires if
the welder has not used the welding process for 6 months
or longer.
A Certificate may be withdrawn by the Employer if there is
reason to doubt the ability of the welder, for example
 A high repair rate.
 Not working in accordance with a qualified WPS.
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Welder Qualification
(according to BS EN ISO 9606)
Typical Welder Essential Variables
 Welding process.
 Material type.
 Electrode type.
 Material thickness.
 Pipe diameter.
 Welding position.
 Weld backing (an unbacked weld requires
more skill).
Copyright © TWI Ltd
Copyright © TWI Ltd
Welder Qualification
(according to BS EN ISO 9606)
Essential variables
Question:
What is a 'welder qualification essential variable'?
(what makes the variable 'essential'?)
Answer:
A variable, that if changed beyond the limits
specified by the EN Standard, may require more
skill than has been demonstrated by the test weld.
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Welder Qualification
Numerous codes and standards deal with welder
qualification, eg BS EN ISO 9606
 Once the content of the procedure is approved the next
stage is to approve the welders to the approved
procedure.
 A welders test know as a Welders Qualification Test
(WQT).
Object of a welding qualification test:
 To give maximum confidence that the welder meets the
quality requirements of the approved procedure (WPS).
 The test weld should be carried out on the same
material and same conditions as for the production
welds.
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8‐6
Welder Qualification
Information that should be included on a welders
test certificate are:
 Welders name and identification number.
 Date of test and expiry date of certificate.
 Standard/code eg BS EN ISO 9606.
 Test piece details.
 Welding process.
 Welding parameters, amps, volts
 Consumables, flux type and filler classification details.
 Sketch of run sequence.
 Welding positions.
 Joint configuration details.
 Material type qualified, pipe diameter etc.
 Test results, remarks.
 Test location and witnessed by.
 Extent (range) of approval.
Welder Qualification
The inspection of a welders qualification test
 It is normal for a qualified inspectors usually from
an independent body to witness the welding.
 Under normal circumstances only one test weld per
welder is permitted.
 If the welder fails the test weld and the failure is
not the fault of the welder eg faulty welding
equipment then a re-test would be permitted.
 The testing of the test weld is done in
accordance with the applicable code.
 It is not normal to carry out tests that test for
the mechanical properties of welds eg tensile,
charpy and hardness tests.
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Copyright © TWI Ltd
Welding Procedures and
Welder Qualifications
Welder Qualification
You are in the process of ensuring that welding
procedures and qualified welders are available
for a new project involving many materials and
processes.
Example:
Welder
Approval
Qualification
Certification
You have to ensure that they all comply with the
TWI specification.
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 1
Within the range of variables in a welding
procedure, DC+ has been stated for the root
pass.
a. This would allow the use of DC- also
b. This would allow the use of AC also
c. In accordance with the Specification, any
polarity could now be used
d. In accordance with the specification only DC+
can be used
Copyright © TWI Ltd
Question 2
Using the TWI specification, which of the
following is true for welder qualifications?
a.
b.
c.
d.
Plate and pipe require separate qualifications
Plate qualifies pipe
Pipe qualifies plate
It depends on whether it is fillet weld or butt
weld
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8‐7
Question 3
Which of the following NDT test is specified for
all types of Stainless steel welds?
a.
b.
c.
d.
Visual
Radiographic
Dye penetrant
All options are correct
Question 4
If a welding current of 145A was used on the
test plate during qualification, on the actual job
while using this procedure, the maximum
current permitted is?
a.
b.
c.
d.
175A
125A
166A
200A
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Copyright © TWI Ltd
Question 5
With respect to the validity of using a procedure in
different positions, which one of the following is
acceptable?
a. Procedure is always valid only for the position
tested
b. Procedure is always valid for all the positions
when impacts are specified
c. Procedure qualified in vertical up position
qualifies for that position only when impacts are
specified
d. Procedure is valid for all positions only for butt
welds when impacts are specified
Question 6
If a welder tests on a plate thickness of 14 mm,
he is qualified to weld which of the following
thicknesses?
a.
b.
c.
d.
14 mm
5-14 mm
5-28 mm
14 mm and above
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Copyright © TWI Ltd
Question 7
For qualifying a welder for butt welding austenitic
stainless steels, 14 mm thick plate, using the TIG
process, which of the following tests are not
required?
a.
b.
c.
d.
Fillet fracture
Macro examination
Hardness tests
All of the above
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Question 8
Which one of the following changes does not
require re-qualification of a welder?
a.
b.
c.
d.
Change from
Change from
Change from
Change from
consumable
PF to PG
fillet to butt
pipe to plate
rutile to low hydrogen
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8‐8
Question 9
Which one of the following is true?
Question 10
If a welder fails a qualification test due to lack of
skill, how many are allowed?
a. Cellulosic qualifies rutile types also
b. PG qualifies PG only
c. The addition of a backing strip requires
requalification
d. Change from argon to carbon dioxide
a.
b.
c.
d.
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One
Two
No retests are allowed
No limit for retests
Copyright © TWI Ltd
8‐9
Se ct ion 9
Ar c En e r gy a n d H e a t I n pu t
9
Arc Energy and Heat Input
9.1
Current and voltage
The amount of electrons on the move defines the amount of electricity that
flows termed current. i and measured in amps, A. Electron flow and therefore
electricity, move at the speed of light as, rather than being the movement of
small solid particles, it is a form of electromagnetic wave, but as this takes us
into the realm of relativity we will not offer a proof of that here. Suffice to say
that, for all practical purposes, electricity is instantaneously available
throughout a circuit.
The differential of the positive and negative used to attract the electrons from
one to the other can be regarded as the driving force. This is called the
potential difference or voltage. Because of this potential there is a tendency
for the electrons to move, ie there is a force attempting to move them from the
negative to the positive. This force is called the electromotive force, (emf),
and is measured in volts, V.
9.2
Arc Energy or heat Input
Amperage and voltage are the two main parameters used when measuring the
welding arc but so is the travel speed. These three variables are used to
calculate the arc energy or heat input, measured in kilo Joules per mm of weld
length. In general, this measurement is from 0.2 to 3.5 Kj per mm but there
are occasions when it can drop below or go above this range.
This measurement is used as a point of reference and is quoted on
documentation, such as a weld procedure. It can have a significant effect on a
materials properties, distortion and residual stress, depending on how high or
low the value is. Therefore, knowing the importance and how to calculate it is
essential for anybody involved in the process.
Arc energy, is generally the term used in conjunction with heat input although
in reality they are different measurements. Arc energy, is the energy generated
at the welding arc using a simple formula. Heat input is the energy generated in
the workpiece from the welding arc using a slightly different formula. Essentially
they are the same thing but once one type of measurement has been selected,
you should not deviate between the two or errors will occur.
American standards use the term heat input but the energy is measured at the
arc wheras the end standards use the term heat input which is the actual
energy transferred to the material. These measurements will be different in
each case, EN generally has lower values as the EN standards take into account
the thermal efficiency value of the welding process know as the “K” factor.
Therefore, the standards dictating which type of measurement shall be recorded
although a Senior Welding Inspector should have a knowledge of both.
Arc energy is reasonably easy to calculate, the amperage and voltage used are
multiplied together and divided by the travel speed in mm per second multiplied
by 1000 to give the Kj per mm.
WIS10-30816
Arc Energy and Heat Input
9-1
Copyright © TWI Ltd
Ex a m ple
A MAG weld is m ade and t he following condit ions wer e r ecorded:



Arc volt s = 24.
Welding am perage = 240.
Trav el speed = 300m m / m inut e.
W h a t is t h e a r c e n e r gy?
Arc energy ( kJ/ m m ) =
Volt s x am ps
Trav el speed ( m m / sec) x 1000
=
24 x 240
( 300/ 60) x 1000
=
5760
5000
Ar c e n e r gy = 1 .1 5 2 or 1 .2 k J/ m m
To calculat e heat input , t he am ount of energy produced in t he work piece, w e
can use t he sam e values as befor e but m ult iply t he am perage and volt age
values by what ’s know as t he efficiency value. This is based on t he fact t hat a
cert ain am ount of ener gy is lost t hrough t he arc and depending on t he welding
process, m ore or less of t his energy is lost . For exam ple, SAW does not lose any
energy m ainly due t o insulat ion of t he granular flux whereas t he TI G process
loses 40% t hr ough conduct ion, conv ect ion and r adiat ion.
Efficiency values via process:



SAW = 1.0.
MI G/ MAG, FCAW and MMAW = 0.8.
TI G and PLASMA = 0.6.
I f w e use t he sam e wor ked exam ple of t he MAG pr ocess but t his t im e calculat e
heat input it will be ev ident t he value has dr opped by 20% . Therefor e, it is
essent ial t hat t he values r ecorded ar e eit her k ept t he sam e or labelled as heat
input or ar c energy.
WI S10- 30816
Arc Energy and Heat I nput
9- 2
Copyright © TWI Lt d
Ex a m ple
A MAG weld is m ade and t he following condit ions wer e r ecorded:



Arc volt s = 24.
Welding am perage = 240.
Trav el speed = 300m m / m inut e.
W ha t is t h e h e a t inpu t ?
Heat input ( kJ/ m m ) =
Volt s x am ps x 0.8 ( efficiency value)
Trav el speed ( m m / sec) x 1000
=
24 x 240 x 0.8
( 300/ 60) x 1000
=
4608
5000
H e a t input = 0 .9 2 k J/ m m
WI S10- 30816
Arc Energy and Heat I nput
9- 3
Copyright © TWI Lt d
Arc Energy and Heat Input
Section 9
Copyright © TWI Ltd
Arc Energy/Heat Input
Copyright © TWI Ltd
Arc Energy/Heat Input
What are the factors that influence arc
energy/heat input?
What is the difference between arc energy
and heat input?
 Amperage.
 Voltage.
 Travel speed.
 Its the Thermal Efficiency Factor known as ”k”
 ASME IX – Heat Input
(but measured as Arc energy)
 BS EN ISO 15614 – Heat Input
(Arc energy x ”k”)
Copyright © TWI Ltd
What's the difference?
 What we call Arc Energy the American
standards reference as Heat Input?
 The difference between EN standards and
American standards is the use of a thermal
efficiency factor in EN known as the ”k” factor
 The ”k” factor denotes the thermal efficiency
value of the process used
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Copyright © TWI Ltd
Arc Energy
The amount of heat generated in the welding arc
per unit length of weld.
 Expressed in kilo Joules per millimetre length
of weld (kJ/mm).
Arc energy (kJ/mm) = Volts x Amps
welding speed(mm/s) x 1000
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9‐1
Heat Input
Heat Input
The energy supplied by the welding arc to the
work piece.
Heat input values for various welding processes
can be calculated from the arc energy by
multiplying by the following
Expressed in terms of
arc energy x thermal efficiency factor
 Thermal efficiency factors;
Thermal efficiency factor is the ratio of heat
energy introduced into the weld to the electrical
energy consumed by the arc.
Copyright © TWI Ltd
Copyright © TWI Ltd
Arc Energy/Heat Input
Thermal efficiency factor k of welding processes
Process No
Process
Factor k
121
Submerged arc welding with wire
1.0
111
Metal-arc welding with covered electrodes
0.8
131
MIG welding
0.8
135
MAG welding
0.8
114
Flux-cored wire metal-arc welding without gas shield
0.8
136
Flux-cored wire metal-arc welding with active gas shield
0.8
137
Flux-cored wire metal-arc welding with inert gas shield
0.8
138
Metal-cored wire metal-arc welding with active gas shield
0.8
139
Metal-cored wire metal-arc welding with inert gas shield
0.8
141
TIG welding
0.6
15
Plasma arc welding
0.6
Arc Energy Calculation
Example
A MAG weld is made and the following conditions
were recorded:
 Arc volts = 24.
 Welding amperage = 240.
 Travel speed = 300mm/minute.
What is the arc energy and heat input?
Copyright © TWI Ltd
Copyright © TWI Ltd
Arc Energy Calculation
AE (kJ/mm) =
=
=
Arc Energy =
Volts x amps
TS (mm/ sec) x 1000
Heat Input
AE (kJ/mm) =
24 x 240
(300/60) x 1000
5760
5000
1.152 or 1.2kJ/mm
Volts x amps x 60 x 0.8
TS (mm/ min) x 1000
=
24 x 240 x 60 x 0.8
300 x 1000
=
276480
300000
Heat Input = 0.92kJ/mm
Copyright © TWI Ltd
Copyright © TWI Ltd
9‐2
Arc Energy/Heat Input
Heat Input and Arc Energy
In the near future your shop floor is likely to get
fabrication jobs involving many critical materials in which
controlling heat input will be required to achieve the
desired properties.
The customer has already provided you with the
specification, the TWI specification, which talks about
welding of many materials and specifies heat input control
for some of them.
It is generally felt by you and your team that a proper
understanding of this vital area is required before initiating
any fabrication activity.
Some of the queries raised during the discussions you had
with your team are as detailed below and trying to answer
them will bring in more clarity and will help in following
correct practices during welding.
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 1
What is the arc energy using process 121 when
the parameters are 24V-225A-250mm per
minute ?
a.
b.
c.
d.
Question 2
The heat input for the TIG welding process using
parameters 20V-125A-50mm per minute will be?
a.
b.
c.
d.
1.3 KJ/mm
1.04KJ/mm
0.57KJ/mm
3.2KJ/mm
2.42KJ/mm
1.02KJ/mm
1.80 KJ/mm
0.8KJ/mm
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 3
Using the preheat tables in the TWI specification,
when welding C-Mn steels having a carbon
equivalent of 0.38 and section combined thickness
of 25 mm using MMA process with hydrogen scale
C and a preheat of 125C with 22V-150A, Which
welding speed falls within the permitted range of
HI?
a.
b.
c.
d.
Question 4
When welding C-Mn steels, having a carbon
equivalent of 0.40 and combined section
thickness of 102 mm, using a preheat of 50C
with MMA process with parameters 24V-100 mm
per min. From those listed which is the
maximum current permitted?
a.
b.
c.
d.
68mm/min
72mm/min
74mm/min
80mm/min
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276A
372A
555A
434A
Copyright © TWI Ltd
9‐3
Question 5
Which of the following is true?
Question 6
Which of the following materials have specific
restrictions on heat input?
a. For a lower heat input, higher preheats are
required
b. For the same material, the heat input
increases with decreasing hydrogen levels
c. As preheat increases, the heat input increases
d. A higher heat input cannot eliminate preheat
a.
b.
c.
d.
Q&T steels
Duplex stainless steels
Aluminium
All of the above options are correct
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Copyright © TWI Ltd
Question 7
Using TIG process for welding 4043 aluminium
alloy having a thickness of 4.2 mm, which of the
following parameters will be acceptable?
a.
b.
c.
d.
20V,
20V,
21V,
20V,
25mm/min,
25mm/min,
25mm/min,
25mm/min,
18A
13A
30A
9A
Question 8
When welding A514 grade material having a
thickness of 15 mm, using a preheat of 100C,
with the MMA process, which of the following
parameters can be acceptable?
a.
b.
c.
d.
24V-210A-200mm/min
20V-210A-200mm/min
24V-210A-150mm/min
25V-250A-200mm/min
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Copyright © TWI Ltd
Question 9
When welding duplex stainless steels, having
23.5% Chromium, using the TIG process, for a
plate thickness of 12 mm, the heat input will be
dependent on?
a.
b.
c.
d.
Question 10
When welding 75mm Q&T steels with a
maximum preheat of 100C, the minimum heat
input is restricted to
a.
b.
c.
d.
The carbon content
The preheat used
Combined plate thickness
None of the above
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2.5KJ/mm
3.2KJ/mm
4.8KJ/mm
5.0KJ/mm
Copyright © TWI Ltd
9‐4
Se ct ion 1 0
Re sidu a l St r e ss a n d D ist or t ion
10
Re sidu a l St r ess a n d D ist or t ion
1 0 .1
W ha t ca use s dist or t ion?
Because welding involves highly localised heat ing of j oint edges t o fuse t he
m at erial, non- uniform st r esses ar e set up in t he com ponent because of
expansion and cont ract ion of t he heat ed m at erial.
I nit ially, com pr essive st resses are cr eat ed in t he sur rounding cold parent m et al
when t he weld pool is for m ed due t o t he t her m al expansion of t he hot m et al
( heat affect ed zone ( HAZ) ) adj acent t o t he weld pool. How ev er , t ensile st resses
occur on cooling when t he cont ract ion of t he weld m et al and im m ediat e HAZ is
resist ed by t he bulk of t he cold parent m et al.
The m agnit ude of t herm al st resses induced int o t he m at erial can be seen by t he
volum e change in t he weld area on solidificat ion and subsequent cooling t o
room t em perat ur e. For exam ple, when welding C- Mn st eel, t he m olt en weld
m et al volum e will be reduced by appr oxim at ely 3% on solidificat ion and t he
volum e of t he solidified weld m et al/ HAZ will be r educed by a furt her 7% as it s
t em perat ur e falls from t he m elt ing point of st eel t o room t em perat ur e.
I f t he st resses generat ed from t herm al expansion/ cont ract ion ex ceed t he yield
st rengt h of t he parent m et al, localised plast ic deform at ion of t he m et al occurs.
Plast ic deform at ion causes a perm anent r educt ion in t he com ponent dim ensions
and dist ort s t he st ruct ur e.
1 0 .2
W ha t a r e t he m a in t y pe s of dist or t ion ?
Dist ort ion occurs in sev eral ways:





Longit udinal shrinkage.
Transv erse shrinkage.
Angular dist ort ion.
Bowing and dishing.
Buckling.
Cont ract ion of t he weld area
and longit udin a l shrinkage.
on
cooling
result s
in
bot h
t r a nsve r se
Non- uniform cont ract ion ( t hrough t hickness) produces a n gula r dist ort ion as
well as longit udinal and t ransv er se shrinking.
For exam ple, in a single V but t weld, t he first weld run produces longit udinal
and t ransverse shrinkage and rot at ion. The second run causes t he plat es t o
rot at e using t he first weld deposit as a fulcrum . Ther efor e balanced welding in a
double side V but t j oint can be used t o pr oduce uniform cont ract ion and prev ent
angular dist ort ion.
Sim ilarly, in a single- sided fillet weld, non- uniform cont ract ion will pr oduce
angular dist ort ion of t he upst anding leg. Double- sided fillet welds can t herefor e
be used t o cont r ol dist ort ion in t he upst anding fillet but because t he weld is only
deposit ed on one side of t he base plat e, angular dist ort ion will now be produced
in t he plat e.
WI S10- 30816
Residual st ress and Dist rort ion
10-1
Copyright © TWI Lt d
Longit udinal bow ing in welded plat es happens when t he w eld cent re is not
coincident wit h t he neut ral axis of t he sect ion so t hat longit udinal shrinkage in
t he welds bends t he sect ion int o a curved shape. Clad plat e t ends t o bow in t wo
direct ions due t o longit udinal and t ransverse shrinkage of t he cladding. This
produces a dished shape.
D ish in g is also produced in st iffened plat ing. Plat es usually dish inwards
bet ween t he st iffener s, because of angular dist ort ion at t he st iffener at t achm ent
welds.
I n plat ing, long range com pressive st r esses can cause elast ic buckling in t hin
plat es, r esult ing in dishing, bowing or rippling, see below.
Ex a m ple s of dist or t ion
Figur e 1 0 .1 Ex a m ple s of dist or t ion.
I ncreasing t he leg lengt h of fillet welds, in part icular, increases shrinkage .
1 0 .3
W h a t a r e t h e fa ct or s a ffe ct in g dist or t ion ?
I f a m et al is uniform ly heat ed and cooled t her e would be alm ost no dist ort ion.
How ev er, because t he m at erial is locally heat ed and rest rained by t he
surr ounding cold m et al, st r esses are generat ed higher t han t he m at erial yield
st ress causing perm anent dist ort ion. The principal fact or s affect ing t he t ype and
degr ee of dist ort ion ar e:





Par ent m at erial propert ies.
Am ount of r est raint .
Joint design.
Part fit - up.
Welding procedur e.
WI S10- 30816
Residual st ress and Dist rort ion
10-2
Copyright © TWI Lt d
1 0 .3 .1
Pa r e n t m a t e r ia l pr ope r t ie s
Par ent m at erial propert ies, which influence dist ort ion, ar e coefficient of t herm al
expansion, t herm al conduct ivit y, and t o a lesser ext ent , yield st ress and
Young’s m odulus. As dist ort ion is det erm ined by expansion and cont r act ion of
t he m at erial, t he coefficient of t herm al expansion of t he m at erial plays a
significant role in det erm ining t he st resses generat ed during welding and,
hence, t he degr ee of dist ort ion. For exam ple, as st ainless st eel has a higher
coefficient of expansion and lesser t herm al conduct ivit y t han plain car bon st eel,
it generally has significant ly m or e dist ort ion.
1 0 .3 .2
Re st r a int
I f a com ponent is w elded wit hout any ext ernal r est r aint , it dist ort s t o r elieve t he
welding st resses. So, m et hods of r est raint , such as st r ongbacks in but t welds,
can prevent m ovem ent and reduce dist ort ion. As r est raint produces higher
levels of residual st ress in t he m at erial, t here is a great er risk of cr acking in
weld m et al and HAZ especially in crack- sensit ive m at erials.
1 0 .3 .3
Joint de sign
Bot h but t and fillet j oint s ar e pr one t o dist ort ion, but it can be m inim ised in but t
j oint s by adopt ing a j oint t ype, which balances t he t herm al st r esses t hrough t he
plat e t hickness. For ex am ple, double- in prefer ence t o a single- sided weld.
Double- sided fillet welds should elim inat e angular dist ort ion of t he upst anding
m em ber, especially if t he t w o w elds are deposit ed at t he sam e t im e.
1 0 .3 .4
Pa r t fit - up
Fit - up should be uniform t o produce pr edict able and consist ent shrinkage.
Excessive j oint gap can also increase t he degr ee of dist ort ion by increasing t he
am ount of weld m et al needed t o fill t he j oint . The j oint s should be adequat ely
t acked t o prevent relat ive m ov em ent bet w een t he part s during welding.
1 0 .3 .5
W e ld ing pr oce d ur e
This influences t he degree of dist ort ion m ainly t hrough it s effect on t he heat
input . As welding procedur es ar e usually select ed for r easons of qualit y and
product ivit y, t he welder has lim it ed scope for r educing dist ort ion. As a general
rule, weld volum e should be kept t o a m inim um . Also, t he welding sequence
and t echnique should aim t o balance t he t herm ally induced st resses ar ound t he
neut ral axis of t he com ponent .
1 0 .4
D ist or t ion - pr e ve nt ion by p r e - se t t in g, pr e - be nd ing or u se of r e st r a int
Dist ort ion can oft en be prev ent ed at t he design st age, for exam ple, by placing
t he w elds about t he neut ral axis, r educing t he am ount of w elding and
deposit ing t he weld m et al using a balanced w elding t echnique. I n designs where
t his is not possible, dist ort ion m ay be prev ent ed by one of t he following
m et hods:



Pre- set t ing of part s.
Pre- bending of part s.
Use of r est raint .
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Residual st ress and Dist rort ion
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Copyright © TWI Lt d
The t echnique chosen will be influenced by t he size and com plexit y of t he
com ponent or assem bly, t he cost of any rest raining equipm ent and t he need t o
lim it residual st resses.
Figur e 1 0 .2 Pr e - se t t ing of pa r t s t o pr oduce cor r e ct a lignm e nt a ft e r w e lding:
a
b
1 0 .4 .1
Pr e - se t t ing of fille t j oint t o pr e ve nt a ngula r dist or t ion;
Pr e - se t t ing of but t j oint t o pr e ve nt a ngula r dist or t ion.
Pr e - se t t in g of pa r t s
The part s ar e pr e- set and left free t o m ove during welding ( see above) . I n
pract ice, t he part s are pre- set by a pre- det er m ined am ount so t hat dist ort ion
occurring during welding is used t o achieve ov erall alignm ent and dim ensional
cont r ol.
The m ain advant ages com par ed wit h t he use of r est raint are t hat t her e is no
expensive equipm ent needed and t here will be lower r esidual st ress in t he
st ruct ur e.
Unfort unat ely, as it is difficult t o predict t he am ount of pre- set t ing needed t o
accom m odat e shrinkage, a num ber of t rial welds will be required. For exam ple,
when MMA or MI G/ MAG welding but t j oint s, t he j oint gap will norm ally close
ahead of w elding; when subm erged ar c welding; t he j oint m ay open up during
welding. When car rying out t rial welds, it is also essent ial t hat t he t est st ruct ure
is reasonably represent at ive of t he full size st r uct ure in order t o generat e t he
level of dist ort ion likely t o occur in pract ice. For t hese r easons, pr e- set t ing is a
t echnique m or e suit able for sim ple com ponent s or assem blies.
Figur e 1 0 .3 Pr e - be nding, u sing st r ongba ck s a nd w e dge s, t o a ccom m oda t e
a ngula r dist or t ion in t hin pla t e s.
1 0 .4 .2
Pr e - be nd ing of p a r t s
Pre- bending, or pr e- springing t he part s before welding is used t o pr e- st ress t he
assem bly t o count eract shrinkage during welding. As shown abov e, pre- bending
by m eans of st rongbacks and wedges can be used t o pre- set a seam before
welding t o com pensat e for angular dist ort ion. Releasing t he wedges aft er
welding will allow t he part s t o m ov e back int o alignm ent .
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Copyright © TWI Lt d
The figure show s t he diagonal bracings and cent re j ack used t o pre- bend t he
fixt ure, not t he com ponent . This count eract s t he dist ort ion int roduced t hough
out - of- balance w elding.
1 0 .4 .3
Use of r e st r a int
Because of t he difficult y in applying pre- set t ing and pre- bending, rest raint is t he
m or e widely pract ised t echnique. The basic principle is t hat t he part s are placed
in posit ion and held under rest raint t o m inim ise any m ov em ent during welding.
When r em oving t he com ponent fr om t he rest raining equipm ent , a relat ively
sm all am ount of m ov em ent will occur due t o locked- in st resses. This can be
cured by eit her applying a sm all am ount of pre- set or st r ess- r elieving befor e
rem oving t he r est raint .
When welding assem blies, all t he com ponent part s should be held in t he corr ect
posit ion unt il com plet ion of welding and a suit ably balanced fabricat ion
sequence used t o m inim ise dist ort ion.
Welding wit h rest raint will generat e addit ional r esidual st resses in t he w eld,
which m ay cause cracking. When w elding suscept ible m at erials, a suit able
welding sequence and t he use of pr eheat ing will reduce t his risk.
Rest raint is relat ively sim ple t o apply using clam ps, j igs and fixt ures t o hold t he
part s during welding.
W e lding j igs a nd fix t ur e s
Jigs and fixt ures are used t o locat e t he par t s and ensure t hat dim ensional
accuracy is m aint ained whilst welding. They can be of a r elat ively sim ple
const ruct ion, as shown in a) below but t he welding engineer will need t o ensur e
t hat t he finished fabricat ion can be r em ov ed easily aft er welding.
Fle x ible cla m ps
A flexible clam p ( b) below) can be effect ive in applying rest raint and also
set t ing- up and m aint aining t he j oint gap ( it can also be used t o close a gap t hat
is t oo wide) .
A disadvant age is t hat as t he rest raining forces in t he clam p will be t ransferr ed
int o t he j oint when t he clam ps are rem ov ed, t he level of residual st ress acr oss
t he j oint can be quit e high.
Figur e 1 0 .4 Re st r a in t t e chnique s t o pr e ve nt dist or t ion.
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Copyright © TWI Lt d
St r ongba ck s ( a nd w e dge s)
St rongback s ar e a popular m eans of applying rest r aint especially for sit e work.
Wedged st rongbacks ( c) ) above) , will prevent angular dist ort ion in plat e and
help prev ent peaking in welding cylindrical shells. As t hese t ypes of st r ongback
will allow t ransver se shrinkage, t he risk of cracking will be great ly reduced
com pared wit h fully welded st rongbacks.
Fully welded st rongbacks ( welded on bot h sides of t he j oint ) ( d) abov e) will
m inim ise bot h angular dist ort ion and t ransver se shrinkage. As significant
st resses can be generat ed across t he w eld, which will increase any t endency for
cracking, car e should be t aken in t he use of t his t ype of st r ongback .
1 0 .4 .4
Be st pr a ct ice
Adopt ing t he following assem bly t echniques will help t o cont r ol dist ort ion:




1 0 .5
Pre- set part s so t hat w elding dist ort ion will achieve ov erall alignm ent and
dim ensional cont rol wit h t he m inim um of r esidual st ress.
Pre- bend j oint edges t o count eract dist ort ion and achieve alignm ent and
dim ensional cont rol wit h m inim um residual st ress.
Apply rest raint during welding by using j igs and fixt ures, flexible clam ps,
st rongbacks and t ack w elding but consider t he risk of cracking which can be
quit e significant , especially for fully welded st rongbacks.
Use an appr ov ed pr ocedure for w elding and rem oval of w elds for r est raint
t echniques, which m ay need preheat t o avoid form ing im perfect ions in t he
com ponent surface.
D ist or t ion - pr e ve nt ion by de sign
D e sign pr inciple s
At t he design st age, welding dist ort ion can oft en be prevent ed, or at least
rest rict ed, by considering:





1 0 .6
Elim inat ion of w elding.
Weld placem ent .
Reducing t he volum e of weld m et al.
Reducing t he num ber of runs.
Use of balanced welding.
Elim in a t ion of w e ldin g
As dist ort ion and shrinkage ar e an inevit able result of welding, good design
requires t hat not only t he am ount of welding is kept t o a m inim um , but also t he
sm allest am ount of weld m et al is deposit ed. Welding can oft en be elim inat ed at
t he design st age by form ing t he plat e or using a st andard r olled sect ion, as
shown below.
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Copyright © TWI Lt d
Figur e 1 0 .5 Elim ina t ion of w e lds by:
a
b
For m ing t he pla t e ;
Use of r olle d or e x t r ude d se ct ion.
I f possible, t he design should use int erm it t ent welds rat her t han a cont inuous
run, t o r educe t he am ount of w elding. For exam ple, in at t aching st iffening
plat es, a subst ant ial reduct ion in t he am ount of welding can oft en be achieved
whilst m aint aining adequat e st r engt h.
1 0 .6 .1
W e ld pla ce m e n t
Placing and balancing of welds ar e im port ant in designing for m inim um
dist ort ion. The closer a weld is posit ioned t o t he neut ral axis of a fabricat ion,
t he lower t he leverage effect of t he shrinkage forces and t he final dist ort ion.
Exam ples of poor and good designs ar e shown below.
Figur e 1 0 .6 D ist or t ion m a y be r e duce d by pla cing t he w e lds a r ou nd t h e ne ut r a l
a x is.
As m ost welds ar e deposit ed away from t he neut ral axis, dist ort ion can be
m inim ised by designing t he fabricat ion so t he shrinkage for ces of an individual
weld are balanced by placing anot her weld on t he opposit e side of t he neut ral
axis. When possible, welding should be carried out alt ernat ely on opposit e
sides, inst ead of com plet ing one side first . I n large st ruct ures, if dist ort ion is
occurring prefer ent ially on one side, it m ay be possible t o t ake corr ect ive
act ions, for ex am ple, by increasing welding on t he ot her side t o cont rol t he
ov erall dist ort ion.
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Copyright © TWI Lt d
1 0 .6 .2
Re du cin g t h e volu m e of w e ld m e t a l
To m inim ise dist ort ion, as well as for econom ic reasons, t he volum e of weld
m et al should be lim it ed t o t he design requirem ent s. For a single- sided j oint , t he
cr oss- sect ion of t he w eld should be k ept as sm all as possible t o reduce t he lev el
of angular dist ort ion, as illust rat ed below.
Figur e 1 0 .7 Re ducin g t h e a m ount of a ngula r dist or t ion a nd la t e r a l sh r in k a ge .
Ways of r educing angular dist ort ion and lat eral shrinkage:



Reducing t he volum e of weld m et al.
Using single pass w eld.
Ensur e fillet welds are not oversize.
Joint preparat ion angle and root gap should be m inim ised pr oviding t he weld
can be m ade sat isfact orily. To facilit at e access, it m ay be possible t o specify a
larger root gap and sm aller preparat ion angle. By cut t ing down t he difference in
t he am ount of weld m et al at t he root and face of t he w eld, t he degr ee of
angular dist ort ion will be cor respondingly reduced. But t j oint s m ade in a single
pass using deep penet r at ion have lit t le angular dist ort ion, especially if a closed
but t j oint can be welded ( see abov e) . For exam ple, t hin sect ion m at erial can be
welded using plasm a and laser welding processes and t hick sect ion can be
welded, in t he v ert ical posit ion, using elect rogas and elect roslag processes.
Alt hough angular dist ort ion can be elim inat ed, t her e will st ill be longit udinal and
t ransv er se shrinkage.
I n t hick sect ion m at er ial, as t he cross- sect ional area of a double V j oint
preparat ion is oft en only half t hat of a single V preparat ion, t he volum e of weld
m et al t o be deposit ed can be subst ant ially r educed. The double V j oint
preparat ion also perm it s balanced welding about t he m iddle of t he j oint t o
elim inat e angular dist ort ion.
As weld shrinkage is pr oport ional t o t he am ount of w eld m et al bot h poor j oint
fit - up and over- welding will increase t he am ount of dist ort ion. Angular
dist ort ion in fillet welds is part icularly affect ed by over- w elding. As design
st rengt h is based on t hroat t hickness, over- welding t o produce a convex w eld
bead does not increase t he allowable design st r engt h but will increase t he
shrinkage and dist ort ion.
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Copyright © TWI Lt d
1 0 .6 .3
Re ducing t h e n um be r of r u ns
Ther e ar e conflict ing opinions on whet her it is bet t er t o deposit a given volum e
of w eld m et al using a sm all num ber of large w eld passes or a large num ber of
sm all passes. Experience shows t hat for a single- sided but t j oint , or fillet weld,
a large single weld deposit gives less angular dist ort ion t han if t he weld is m ade
wit h a num ber of sm all runs. Generally, in an unrest rained j oint , t he degr ee of
angular dist ort ion is approxim at ely proport ional t o t he num ber of passes.
Com plet ing t he j oint wit h a sm all num ber of large weld deposit s result s in m ore
longit udinal and t ransverse shrinkage t han a w eld com plet ed in a larger num ber
of sm all passes. I n a m ult i- pass weld, previously deposit ed weld m et al provides
rest raint , so t he angular dist ort ion per pass decr eases as t he w eld is built up.
Large deposit s also incr ease t he risk of elast ic buckling part icularly in t hin
sect ion plat e.
1 0 .6 .4
Use of ba la nce d w e lding
Balanced welding is an effect ive m eans of cont rolling angular dist or t ion in a
m ult i- pass but t weld by arranging t he welding sequence t o ensur e t hat angular
dist ort ion is cont inually being corr ect ed and not allowed t o accum ulat e during
welding. Com parat ive am ount s of angular dist ort ion from balanced w elding and
welding one side of t he j oint first are show n below. The balanced welding
t echnique can also be applied t o fillet j oint s.
Figur e 1 0 .8 Ba la nce d w e lding t o r e duce t he a m oun t of a ngula r dist or t ion.
I f w elding alt ernat ely on eit her side of t he j oint is not possible, or if one side
has t o be com plet ed first , an asym m et rical j oint preparat ion m ay be used wit h
m or e weld m et al being deposit ed on t he second side. The great er cont ract ion
result ing from deposit ing t he weld m et al on t he second side will help count eract
t he dist ort ion on t he first side.
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Copyright © TWI Lt d
1 0 .6 .5
Be st pr a ct ice
The following design principles can cont rol dist ort ion:






Elim inat e welding by for m ing t he plat e and using rolled or ext ruded
sect ions.
Minim ise t he am ount of weld m et al.
Do not ov er- weld.
Use int erm it t ent welding in preference t o a cont inuous weld pass.
Place welds about t he neut ral axis.
Balance t he welding about t he m iddle of t he j oint by using a double V j oint
in preference t o a single.
Adopt ing best pract ice principles can hav e surprising cost benefit s. For exam ple,
for a design fillet leg lengt h of 6m m , deposit ing an 8m m leg lengt h will result in
t he deposit ion of 57% addit ional weld m et al. Besides t he ext r a cost of
deposit ing weld m et al and t he increase risk of dist ort ion, it is cost ly t o rem ov e
t his ext ra w eld m et al lat er. How ev er , designing for dist ort ion cont r ol m ay incur
addit ional fabricat ion cost s. For exam ple, t he use of a double V j oint
preparat ion is an excellent way t o reduce weld volum e and cont r ol dist ort ion,
but ext ra cost s m ay be incurred in product ion t hrough m anipulat ion of t he
wor kpiece for t he w elder t o access t he r ev erse side.
1 0 .7
D ist or t ion - pr e ve nt ion by f a br ica t ion t e ch nique s
1 0 .7 .1
Asse m bly t e ch nique s
I n general, t he welder has lit t le influence on t he choice of w elding procedur e
but assem bly t echniques can oft en be crucial in m inim ising dist or t ion. The
principal assem bly t echniques ar e:



Tack welding.
Back- t o- back assem bly.
St iffening.
Ta ck w e ldin g
Tack w elds are ideal for set t ing and m aint aining t he j oint gap but can also be
used t o r esist t ransverse shrinkage. To be effect ive, t hought should be given t o
t he num ber of t ack w elds, t heir lengt h and t he dist ance bet w een t hem . Wit h t oo
few, t here is t he risk of t he j oint progr essively closing up as welding proceeds.
I n a long seam , using MMA or MI G/ MAG, t he j oint edges m ay ev en overlap. I t
should be not ed t hat w hen using t he subm erged arc pr ocess, t he j oint m ight
open up if not adequat ely t acked.
The t ack w elding sequence is im port ant t o m aint ain a uniform root gap along
t he lengt h of t he j oint . Thr ee alt ernat ive t ack- welding sequences are show n
below:



Tack weld st raight t hrough t o t he end of t he j oint a) . I t is necessary t o
clam p t he plat es or t o use wedges t o m aint ain the j oint gap during t acking.
Tack w eld one end and t hen use a back st epping t echnique for t acking t he
rest of t he j oint b) .
Tack weld t he cent r e and com plet e t he t ack w elding by back st epping c) .
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Figur e 1 0 .9 Alt e r na t ive pr oce dur e s use d for t a ck w e lding t o pr e ve nt t r a nsve r se
shr in k a ge .
Direct ional t acking is a useful t echnique for cont r olling t he j oint gap, for
exam ple closing a j oint gap which is ( or has becom e) t oo wide.
When t ack welding, it is im port ant t hat t acks which are t o be fused int o t he
m ain weld, are pr oduced t o an approv ed pr ocedure using appropriat ely qualified
welders. The pr ocedure m ay require preheat and an approv ed consum able as
specified for t he m ain weld. Rem oval of t he t acks also needs careful cont r ol t o
avoid causing defect s in t he com ponent sur face.
Ba ck - t o- ba ck a sse m bly
By t ack w elding or clam ping t wo ident ical com ponent s back- t o- back , w elding of
bot h com ponent s can be balanced around t he neut ral axis of t he com bined
assem bly ( see a) on next page) . I t is recom m ended t hat t he assem bly is st ressrelieved befor e separat ing t he com ponent s. I f st ress- relieving is not done, it
m ay be necessar y t o insert wedges bet w een t he com ponent s ( b) on next page)
so when t he wedges ar e rem oved, t he part s will m ove back t o t he cor r ect shape
or alignm ent .
Figur e 1 0 .1 0 Ba ck - t o- ba ck a sse m bly t o con t r ol dist or t ion w he n w e lding t w o
ide nt ica l com pone nt s:
a
b
Asse m blie s t a ck e d t oge t he r be for e w e lding;
Use of w e dge s for com pone nt s t ha t dist or t on se pa r a t ion a ft e r w e ldin g.
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Copyright © TWI Lt d
St iffe ning
Figur e 1 0 .1 1 Longit udina l st iffe ne r s pr e ve nt bow ing in but t w e lde d t hin pla t e
j oint s.
Longit udinal shrinkage in but t welded seam s oft en r esult s in bowing, especially
when fabricat ing t hin plat e st ruct ures. Longit udinal st iffeners in t he for m of flat s
or angles, welded along each side of t he seam ( see abov e) ar e effect ive in
prev ent ing longit udinal bowing. St iffener locat ion is im port ant : t hey m ust be at
a sufficient dist ance fr om t he j oint so t hey do not int erfere wit h welding, unless
locat ed on t he r ev erse side of a j oint welded from one side.
1 0 .7 .2
W e ld ing pr oce d ur e
A suit able welding procedur e is usually det erm ined by product ivit y and qualit y
requirem ent s rat her t han t he need t o cont r ol dist ort ion. Nevert heless, t he
welding process, t echnique and sequence do influence t he dist ort ion level.
W e lding pr oce ss
General rules for select ing a welding process t o prev ent angular dist ort ion ar e:


Deposit t he weld m et al as quickly as possible.
Use t he least num ber of runs t o fill t he j oint .
Unfort unat ely, select ing a suit able welding process based on t hese rules m ay
increase longit udinal shrinkage r esult ing in bowing and buckling.
I n m anual welding, MI G/ MAG, a high deposit ion rat e pr ocess, is preferr ed t o
MMA. Weld m et al should be deposit ed using t he largest diam et er elect r ode
( MMA) , or t he highest curr ent level ( MI G/ MAG) , wit hout causing lack- of- fusion
im perfect ions. As heat ing is m uch slower and m or e diffuse, gas welding
norm ally produces m or e angular dist ort ion t han t he ar c pr ocesses.
Mechanised t echniques com bining high deposit ion rat es and welding speeds
have t he gr eat est pot ent ial for pr ev ent ing dist ort ion. As t he dist ort ion is m or e
consist ent , sim ple t echniques such as pr e- set t ing are m or e effect ive in
cont r olling angular dist ort ion.
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Copyright © TWI Lt d
W e lding t e ch nique
General rules for pr ev ent ing dist ort ion are:



Keep t he w eld ( fillet ) t o t he m inim um specified size.
Use balanced w elding about t he neut ral axis.
Keep t he t im e bet w een runs t o a m inim um .
Figur e 1 0 .1 2 Angula r dist or t ion of t he j oint a s de t e r m ine d by t he n um be r of
r un s in t he fille t w e ld.
I n t he absence of rest r aint , angular dist ort ion in bot h fillet and but t j oint s will
be a funct ion of t he j oint geom et ry , w eld size and t he num ber of r uns for a
given cross- sect ion. Angular dist ort ion ( m easured in degrees) as a funct ion of
t he num ber of runs for a 10m m leg lengt h fillet weld is shown above.
I f possible, balanced welding around t he neut ral axis should be done, for
exam ple on double- sided fillet j oint s, by t wo people w elding sim ult aneously. I n
but t j oint s, t he run order m ay be crucial in t hat balanced welding can be used
t o cor rect angular dist or t ion as it develops.
Figur e 1 0 .1 3 Use of w e lding dir e ct ion t o cont r ol dist or t ion:
a
b
Ba ck - st e p w e lding;
Sk ip w e lding.
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W e ldin g se qu e n ce
The w elding sequence, or direct ion, of w elding is im port ant and should be
t owards t he fr ee end of t he j oint . For long welds, t he whole of t he w eld is not
com plet ed in one direct ion. Short runs, for exam ple using t he back- st ep or skip
welding t echnique, ar e very effect ive in dist ort ion cont rol ( see abov e) .


1 0 .7 .3
Back- st ep welding involves deposit ing short adj acent weld lengt hs in t he
opposit e direct ion t o t he general progression ( see above) .
Skip welding is laying short weld lengt hs in a pre- det erm ined, evenly
spaced, sequence along t he seam ( b) in above figure) . Weld lengt hs and t he
spaces bet w een t hem are generally equal t o t he nat ural run- out lengt h of
one elect rode. The direct ion of deposit for each elect r ode is t he sam e, but it
is not necessary for t he welding direct ion t o be opposit e t o t he direct ion of
general progr ession.
Be st pr a ct ice
The following fabricat ion t echniques ar e used t o cont r ol dist ort ion:





1 0 .8
Using t ack welds t o set - up and m aint ain t he j oint gap.
I dent ical com ponent s welded back- t o- back so w elding can be balanced
about t he neut r al axis.
At t achm ent of longit udinal st iffener s t o prevent longit udinal bowing in but t
welds of t hin plat e st ruct ures.
Wher e t her e is choice of w elding procedur e, process and t echnique should
aim t o deposit t he weld m et al as quickly as possible; MI G/ MAG in
preference t o MMA or gas w elding and m echanised rat her t han m anual
welding.
I n long runs, t he whole w eld should not be com plet ed in one direct ion;
back- st ep or skip welding t echniques should be used.
D ist or t ion - cor r e ct iv e t e chnique s
Ev er y effort should be m ade t o avoid dist ort ion at t he design st age and by
using suit able fabricat ion pr ocedur es. As it is not always possible t o av oid
dist ort ion during fabricat ion, sev eral w ell- est ablished corr ect ive t echniques can
be em ploy ed. Reworking t o cor rect dist ort ion should not be undert aken light ly
as it is cost ly and needs consider able skill t o avoid dam aging t he com ponent .
General guidelines ar e provided on best pr act ice for corr ect ing dist ort ion using
m echanical or t herm al t echniques.
1 0 .8 .1
M e cha nica l t e chn ique s
The principal m echanical t echniques are ham m ering and pressing. Ham m ering
m ay cause surface dam age and w or k hardening.
I n cases of bowing or angular dist ort ion, t he com plet e com ponent can oft en be
st raight ened on a pr ess wit hout t he disadvant ages of ham m ering. Packing
pieces are insert ed bet ween t he com ponent and t he plat ens of t he press. I t is
im port ant t o im pose sufficient deform at ion t o give over- cor rect ion so t hat t he
norm al elast ic spring- back will allow t he com ponent t o assum e it s corr ect
shape.
WI S10- 30816
Residual st ress and Dist rort ion
10-14
Copyright © TWI Lt d
Figur e 1 0 .1 4 Use of pr e ss t o cor r e ct bow in g in T but t j oin t .
Pressing t o cor r ect bowing in a flanged plat e is shown above. I n long
com ponent s, dist ort ion is rem oved progr essively in a series of incr em ent al
pressings; each one act ing over a short lengt h. I n t he case of t he flanged plat e,
t he load should act on t he flange t o prevent local dam age t o t he web at t he
load point s. As increm ent al point loading will only produce an approxim at ely
st raight com ponent , it is bet t er t o use a form er t o achieve a st raight com ponent
or t o produce a sm oot h curvat ur e.
Be st pr a ct ice for m e ch a n ica l st r a igh t e nin g
The following should be adopt ed when using pressing t echniques t o r em ov e
dist ort ion:




Use packing pieces which will over corr ect t he dist ort ion so t hat spring- back
will ret urn t he com ponent t o t he corr ect shape.
Check t hat t he com ponent is adequat ely support ed during pressing t o
prev ent buckling.
Use a for m er ( or r olling) t o achieve a st raight com ponent or produce a
curvat ur e.
As unsecured packing pieces m ay fly out fr om t he press, t he following safe
pract ice m ust be adopt ed:
฀
฀
฀
1 0 .8 .2
Bolt t he packing pieces t o t he plat en.
Place a m et al plat e of adequat e t hickness t o int er cept t he m issile.
Clear personnel fr om t he hazard ar ea.
The r m a l t e ch nique s
The basic principle behind t herm al t echniques is t o creat e sufficient ly high local
st resses so t hat , on cooling, t he com ponent is pulled back int o shape.
Figur e 1 0 .1 5 Loca lise d he a t ing t o cor r e ct dist or t ion.
WI S10- 30816
Residual st ress and Dist rort ion
10-15
Copyright © TWI Lt d
This is achieved by locally heat ing t he m at erial t o a t em perat ur e wher e plast ic
deform at ion will occur as t he hot , low yield st rengt h m at erial t ries t o expand
against t he surrounding cold, higher yield st rengt h m et al. On cooling t o room
t em perat ur e t he heat ed area will at t em pt t o shr ink t o a sm aller size t han befor e
heat ing. The st resses generat ed t her eby will pull t he com ponent int o t he
required shape ( see above) .
Local heat ing is, t herefor e, a relat ively sim ple but effect ive m eans of corr ect ing
welding dist ort ion. Shrinkage level is det erm ined by size, num ber, locat ion and
t em perat ur e of t he heat ed zones. Thickness and plat e size det erm ines t he area
of t he heat ed zone. Num ber and placem ent of heat ing zones are largely a
quest ion of experience. For new j obs, t est s will oft en be needed t o quant ify t he
level of shrinkage.
Spot , lin e , or w e dge - sha pe d heat ing t echniques can all be used in t herm al
corr ect ion of dist ort ion.
Spot he a t in g
Figur e 1 0 .1 6 Spot he a t ing for cor r e ct ing buck ling.
Spot heat ing is used t o rem ov e buckling, for exam ple when a relat ively t hin
sheet has been w elded t o a st iff fram e. Dist ort ion is corr ect ed by spot heat ing
on t he conv ex side. I f t he buckling is regular, t he spot s can be arranged
sym m et rically, st art ing at t he cent r e of t he buckle and wor king out war ds.
Line h e a t ing
Figur e 1 0 .1 7 Line he a t ing t o cor r e ct a n gula r dist or t ion in a fille t w e ld.
WI S10- 30816
Residual st ress and Dist rort ion
10-16
Copyright © TWI Lt d
Heat ing in st raight lines is oft en used t o cor rect angular dist ort ion, for exam ple,
in fillet welds. The com ponent is heat ed along t he line of t he welded j oint but
on t he opposit e side t o t he w eld so t he induced st resses will pull t he flange flat .
W e dge - sh a pe d he a t in g
To cor rect dist ort ion in larger com plex fabricat ions it m ay be necessar y t o heat
whole areas in addit ion t o em ploying line heat ing. The pat t ern aim s at shrinking
one part of t he fabricat ion t o pull t he m at erial back int o shape.
Figur e 1 0 .1 8 Use of w e dge sha pe d he a t in g t o st r a ight e n pla t e .
Apart fr om spot heat ing of t hin panels, a wedge- shaped heat ing zone should be
used fr om base t o apex and t he t em perat ur e profile should be uniform t hrough
t he plat e t hickness. For t hicker sect ion m at erial, it m ay be necessary t o use t w o
t orches, one on each side of t he plat e.
As a general guideline, t o st raight en a curved plat e wedge dim ensions should
be:


Lengt h of w edge - t wo- t hirds of t he plat e widt h.
Widt h of wedge ( base) - one sixt h of it s lengt h ( base t o apex) .
The degr ee of st raight ening will t ypically be 5m m in a 3m lengt h of plat e.
Wedge- shaped heat ing can be used t o cor rect dist ort ion in a variet y of
sit uat ions, ( see below) :



St andard r olled sect ion, which needs corr ect ion in t wo planes a) .
Buckle at edge of plat e as an alt ernat ive t o rolling b) .
Box sect ion fabricat ion, which is dist ort ed out of plane c) .
WI S10- 30816
Residual st ress and Dist rort ion
10-17
Copyright © TWI Lt d
a) St andard rolled st eel
sect ion
b) Buckled edge of plat e
c) Box fabricat ion
Figur e 1 0 .1 9 W e dge sha pe d he a t ing t o cor r e ct dist or t ion.
Ge n e r a l pr e ca ut ions
The danger s of using t herm al st raight ening t echniques are t he risk of ov ershrinking t oo large an area or causing m et allurgical changes by heat ing t o t oo
high a t em perat ur e. As a general rule, when cor rect ing dist ort ion in st eels t he
t em perat ur e of t he ar ea should be rest rict ed t o approxim at ely t o 600- 650°C dull red heat .
I f t he heat ing is int errupt ed, or t he heat lost , t he operat or m ust allow t he m et al
t o cool and t hen begin again.
Be st pr a ct ice for dist or t ion cor r e ct ion by t he r m a l h e a t ing
The following should be adopt ed when using t herm al t echniques t o rem ov e
dist ort ion:






Use spot heat ing t o rem ov e buckling in t hin sheet st ruct ur es.
Ot her t han in spot heat ing of t hin panels, use a wedge- shaped heat ing
t echnique.
Use line heat ing t o cor r ect angular dist ort ion in plat e.
Rest rict t he ar ea of heat ing t o avoid over- shrinking t he com ponent .
Lim it t he t em per at ure t o 600- 650°C ( dull red heat ) in st eels t o pr event
m et allurgical dam age.
I n w edge heat ing, heat fr om t he base t o t he apex of t he wedge, penet rat e
ev enly t hrough t he plat e t hickness and m aint ain an ev en t em per at ure.
WI S10- 30816
Residual st ress and Dist rort ion
10-18
Copyright © TWI Lt d
Residual Stress
Residual stresses are undesirable because
Residual Stress and Distortion
 They lead to distortions.
 They affect dimensional stability of the welded
assembly.
 They enhance the risk of brittle fracture.
 They can facilitate certain types of corrosion.
Factors affecting residual stresses
Section 10





Copyright © TWI Ltd
Factors Affecting Residual Stress
Parent material properties
 Thermal expansion coefficient - the greater
the value, the greater the residual stress.
 Yield strength - the greater the value, the
greater the residual stress.
 Young’s modulus - the greater the value
(increase in stiffness), the greater the residual
stress.
 Thermal conductivity - the higher the value,
the lower the residual stress.
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Factors Affecting Residual Stress
Welding sequence
 Number of passes - every pass adds to the
total contraction.
 Heat input - the higher the heat input, the
greater the shrinkage.
 Travel speed - the faster the welding speed,
the less the stress.
 Build-up sequence.
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Parent material properties.
Amount of restrain.
Joint design.
Fit-up.
Welding sequence.
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Factors Affecting Residual Stress
Joint design
 Weld metal volume.
 Type of joint - butt vs. fillet, single vs. double side.
Amount of restrain
 Thickness - as thickness increase, so do the stresses.
 High level of restrain lead to high stresses.
 The lack of pre heat will increase stresses.
Fit-up
 Misalignment may reduce stresses in some cases.
 Root gap - increase in root gap increases shrinkage.
Copyright © TWI Ltd
Factors Affecting Residual Stress
Residual stresses
 Are a result of local plastic deformation.
 Are a result of non uniform heating and
cooling ie welding.
 Are a result of non uniform heating, cooling,
expansion and contraction.
 This is because the expansion and contraction
can be obstructed by colder surrounding
materials and also the mechanical properties
of the material being welded.
Copyright © TWI Ltd
10‐1
Nature of Residual Stress
Residual Stress
Heating and cooling leads
to expansions and
contractions.
If expansion is hindered,
compressive stresses
occur.
The material as shown
can expand and contract
freely without hindrance.
If on cooling shrinkage is
obstructed, tensile
stresses occur.
A welded joint does not
react in this way!
The overall result,
Residual Stresses.
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Residual Stress
Origins of residual stress in welded joints
Cold weld unfused
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Factors Affecting Residual Stress
Residual stresses
 Temperatures higher than 600°C, depending
on the restraint, plastic deformation occurs
(distortion).
 Temperatures lower than 600°C, depending on
restraint, residual stresses occur because
temperature not high enough to yield the
material sufficiently.
Hot weld
Cold weld fused
Copyright © TWI Ltd
Copyright © TWI Ltd
Types of Residual Stress
Longitudinal residual stress after welding
Maximum stress = YS at room temperature
Types of Residual Stress
Residual stress after welding
Compression
Tension
Tension
YS at room
temperature
Compression
The longer the weld, the higher the tensile stress!
The higher the heat input the wider the tensile zone!
Copyright © TWI Ltd
Copyright © TWI Ltd
10‐2
Residual Stress
Reducing residual stresses
 The most effective way to reduce residual
stresses is to post weld heat treat uniformly.
 The most effective method is to PWHT the
whole member but this is not always possible.
 A controlled local, uniform PWHT usually
reduces stresses by 75%.
Residual Stress
Post weld heat treatment
 Controlled ramp up to soak temperature so
that complex items are heated uniformly and
distortion does not take place.
 Held at soak temperature for approximately
one hour for every 25mm of thickness.
 Controlled reduction of temperature.
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Copyright © TWI Ltd
Heat Treatment Methods
Heat Treatment Methods
Advantages
 Ability to vary heat.
 Ability to continuously
maintain heat.
Advantages:
 High heating rates.
 Ability to heat a
narrow band.
Disadvantages
 Elements may burn
out or arcing during
heating.
Disadvantages
 High equipment cost.
 Large equipment,
less portable.
HF local heat treatment
Local heat treatment using
electric heating blankets
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Copyright © TWI Ltd
Distortion
TEMP
650°C
YIELD
Factors affecting distortion
 Parent material properties.
 Amount of restrain.
 Joint design.
 Fit-up.
 Welding sequence.
Randomly
Uniformed
Stressed
Structure
Structure
Soak Time
STRESS
TIME
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Copyright © TWI Ltd
10‐3
Factors Affecting Distortion
Parent material properties
 Thermal expansion coefficient - the greater
the value, the greater the residual stress.
 Yield strength - the greater the value, the
greater the residual stress.
 Thermal conductivity - the higher the value,
the lower the residual stress.
Factors Affecting Distortion
Welding sequence
 Number of passes - every pass adds to the
total contraction.
 Travel speed - the faster the welding speed,
the less the stress.
 Build-up sequence.
Copyright © TWI Ltd
Types of Distortion
Angular distortion
Copyright © TWI Ltd
Distortion Prevention
Distortion prevention by design
Consider eliminating the welding!!
a) By forming the plate.
b) By use of rolled or extruded sections.
Copyright © TWI Ltd
Distortion Prevention
Distortion prevention by design
Copyright © TWI Ltd
Distortion Prevention
Distortion prevention by design
 Use of balanced welding.
 Consider weld
Placement.
 Reduce weld metal
volume and/or number
of runs.
Copyright © TWI Ltd
Copyright © TWI Ltd
10‐4
Distortion Prevention
Distortion prevention by fabrication techniques
Residual Stress and Distortion
You are currently employed as a Senior Welding
Inspector on a fabricated steel structure.
The structure has many different joint
configurations with a thickness range from
12.5mm up to 50mm.
All welding to be completed by either the SAW or
MMA welding processes.
Control welding techniques by
a) Back-step welding.
b) Skip welding.
One of your main tasks is to ensure both stress
and distortion is kept to a minimum.
Copyright © TWI Ltd
Question 1
Residual stresses would play a major part in
which of the following
a.
b.
c.
d.
HICC and brittle fracture
Lamellar tearing and solidification cracking
Fatigue and ductile failure
Chevron cracking and hot cracking
Copyright © TWI Ltd
Question 3
Which combination of factors will increase the
level of distortion?
a. High Rm, high thermal conductivity and low
coefficient of expansion
b. Low Re, low thermal conductivity and high
coefficient of expansion
c. High yield, high UTS and low coefficient of
expansion
d. Low percentage Z, High percentage of
Sulphur and Phosphorous
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 2
Which of the following conditions would cause
the greatest amount of distortion on this type of
fabricated structure?
a. A highly restrained joint during welding
b. A joint, which is free to move during welding
c. A joint, which would be subjected to the
lowest heat input
d. 2 options are correct
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Question 4
The fabrication contains materials of varying Re
values, generally which of the following would
you expect to distort the most without control
methods in place?
a. Welded joints made from the highest Re
value materials
b. Welded joints made from the lowest Re value
materials
c. Welded joints that contain the highest
residual stress
d. 2 options are correct
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10‐5
Question 5
Part of the fabrication contains a joint made from
C/Mn steel welded to a 316L steel. Which of the
following best applies when considering distortion?
a. The C/Mn steel side of the joint will distort the
most due to high thermal expansion
b. The C/Mn steel side of the joint will distort the
most due to low thermal conductivity
c. The 316L side of the joint will distort the most due
to high thermal conductivity
d. The 316L side of the joint will distort the most due
to low thermal conductivity
Question 6
Which of the following are factors affecting
distortion?
a.
b.
c.
d.
Parent material properties
Joint design/amount of restraint
Heat input/welding sequence
All options are correct
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Copyright © TWI Ltd
Question 7
The fabricator approaches you on the best way to
reduce distortion. The joint configuration, welding
process, material type can’t be changed. Which of
the following could be applied to reduce distortion?
a. Increase restraint and minimize the amount of
weld beads deposited, heavier weld beads
b. Reduce restraint and minimize the amount of weld
beads deposited, heavier weld beads
c. Increase restraint and maximize the amount of
weld beads deposited, lighter weld beads
d. Reduce restraint and increase the amount of weld
beads deposited, heavier weld beads
Copyright © TWI Ltd
Question 9
After welding it is a requirement to conduct a
PWHT on certain welded joints. On this welded
structure what is the main purpose of this heat
treatment?
a. Normalising the material to increase the UTS
value for the welded structure
b. For hydrogen release, especially if a E8016
electrodes had been used for the welding of
the joint.
c. For stress relieving the welded joint
d. To anneal and temper the weld metal
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Question 8
Which of the following thickness and joint
configurations would you expect to produce the
highest amount of distortion?
a.
b.
c.
d.
25.5mm single V butt
50mm single U butt
50mm double U butt
25.5mm single J butt
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Question 10
One of your inspectors asks you what would a typical
PWHT temperature be, when applied to this
fabrication. Which of the following would be the
correct answer when taking into account the material
thickness range stated on a C/Mn to C/Mn steel
welded joint?
a. Approximately 50°C above the upper critical limit
of the material stated
b. Between 600°C to 650°C
c. Approximately 100°C lower than the lower critical
limit of the material stated
d. 2 options are correct
Copyright © TWI Ltd
10‐6
Se ct ion 1 1
W e lda bilit y of St e e ls
11
W e lda bilit y of St e e ls
The t erm w eldabilit y sim ply m eans t he abilit y t o be w elded and m any t ypes of
st eel t hat are w eldable have been dev eloped for a wide range of applicat ions.
How ev er, it is t he ease or difficult y of m aking a weld wit h suit able propert ies
and fr ee from defect s which det erm ines whet her st eels are consider ed as
having ‘good w eldabilit y’ or said t o have poor w eldabilit y. A st eel is usually said
t o have poor weldabilit y if it is necessar y t ak e special precaut ions t o av oid a
part icular t ype of im per fect ion. Anot her r eason m ay be t he need t o w eld wit hin
a very narr ow range of param et er s t o achieve propert ies r equired for t he j oint .
1 1 .1
Fa ct or s t ha t a ffe ct w e lda bilit y
A num ber of int er- r elat ed fact or s det erm ine whet her a st eel is said t o have
good or poor w eldabilit y. These ar e:




Act ual chem ical com posit ion.
Weld j oint configurat ion.
Welding process t o be used.
Propert ies r equired from t he w eldm ent s.
For st eels wit h poor weldabilit y it is part icularly necessary t o ensur e t hat :



Welding procedure specificat ions give welding condit ions t hat do not cause
cracking but achieve t he specified propert ies.
Welders w ork st rict ly in accordance wit h t he specified welding condit ions.
Welding inspect or s r egularly m onit or welders t o ensure t hey are w orking
st rict ly in accordance t he WPSs.
Having a good underst anding of t he charact erist ics, causes, and ways of
avoiding im perfect ions in st eel weldm ent s should enable welding inspect or s t o
focus at t ent ion on t he m ost influent ial welding param et ers when st eels wit h
poor w eldabilit y are being used.
1 1 .2
H ydr oge n cr a ck in g
During fabricat ion by w elding, crack s can occur in som e t ypes of st eel, due t o
t he pr esence of hydr ogen. The t echnical nam e for t his t ype of cr acking is
hydrogen induced cold cracking ( HI CC) but it is oft en r efer r ed t o by ot her
nam es t hat describe var ious charact erist ics of hydrogen cracks:




Cold cracking - crack s occur when t he weld has cooled down.
HAZ cracking - cracks t end t o occur m ainly in t he HAZ.
Delayed cracking - cracks m ay occur som e t im e aft er w elding has finished
( possibly up t o ~ 48h) .
Underbead cracking - cr acks occur in t he HAZ beneat h a weld bead.
Alt hough m ost hydrogen cracks occur in t he HAZ, t here are circum st ances when
t hey m ay form in weld m et al.
Figure 11.1 show s t ypical locat ions of HAZ hydr ogen cracks.
Figure 11.2 show s hydr ogen crack in t he HAZ of a fillet weld.
WI S10- 30816
Weldabilit y of St eels
11-1
Copyright © TWI Lt d
1 1 .2 .1
Fa ct or s inf lu e ncing susce pt ibilit y t o h ydr oge n cr a ck in g
Hydr ogen cracking in t he HAZ of a st eel occurs when 4 con dit ion s e x ist a t
t he sa m e t im e :
H ydr oge n le v e l
St r e ss
Te m pe r a t u r e
Susce pt ible m icr ost r u ct ur e
>
>
<
>
1 5 m l/ 1 0 0 g of w e ld m e t a l de posit e d
0 .5 of t he y ie ld st r e ss
3 0 0 0C
4 0 0 H V ha r dne ss
These four condit ions ( four fact ors) ar e m ut ually int erdependent so t hat t he
influence of one condit ion ( it s’ act ive level) depends on how act ive t he ot hers
t hree fact or s are.
1 1 .2 .2
Cr a ck ing m e ch a nism
Hydr ogen ( H) can ent er t he m olt en weld m et al when hydrogen cont aining
m olecules ar e broken down int o H at om s in t he welding arc.
Because H at om s are v er y sm all t hey can m ove about ( diffuse) in solid st eel
and while weld m et al is hot t hey can diffuse t o t he weld surface and escape int o
t he at m ospher e.
How ev er, at lower t em perat ur es H cannot diffuse as quickly and if t he
weldm ent cools down quickly t o am bient t em perat ur e H will becom e t rapped usually t he HAZ.
I f t he HAZ has a suscept ible m icrost ruct ure – indicat ed by being relat ively hard
and brit t le, t here ar e also r elat ively high t ensile st r esses in t he weldm ent t hen
H cracking can occur.
The pr ecise m echanism t hat causes crack s t o form is com plex but H is believed
t o cause em brit t lem ent of regions of t he HAZ so t hat high- localised st resses
cause cracking rat her t han plast ic st raining.
1 1 .2 .3
Avoiding H AZ h ydr oge n cr a ck ing
Because t he fact or s t hat cause cracking are int erdependent , and each need t o
be at an act ive level at t he sam e t im e, cracking can be avoided by ensuring t hat
at least one of t he four fact or s is not act ive during welding.
Met hods t hat can be used t o m inim ise t he influence of each of t he four fact or s
are considered in t he following sub- sect ions.
WI S10- 30816
Weldabilit y of St eels
11-2
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H ydr oge n
The principal source of hydrogen is m oist ure ( H 2 O) and t he principal sour ce of
m oist ure is welding flux. Som e fluxes cont ain cellulose and t his can be a very
act ive source of hydrogen.
Welding processes t hat do not require flux can be regarded as low hydrogen
processes.
Ot her sources of hydr ogen are m oist ure pr esent in rust or scale, and oils and
greases ( hydr ocarbons) .
Reducing t he influence of hydrogen is possible by:










Ensuring t hat fluxes ( coat ed elect rodes, flux- cor ed wires and SAW fluxes)
are low in H when w elding com m ences.
Low H elect rodes m ust be eit her bak ed & t hen st or ed in a hot holding ov en
or supplied in vacuum - sealed packages.
Basic agglom erat ed SAW fluxes should be k ept in a heat ed silo befor e issue
t o m aint ain t heir as- supplied, low m oist ure, condit ion.
Check t he diffusible hydrogen cont ent of t he weld m et al ( som et im es it is
specified on t he t est cer t ificat e) .
Ensuring t hat a low H condit ion is m aint ained t hroughout welding by not
allowing fluxes t o pick- up m oist ure fr om t he at m ospher e.
Low hydr ogen elect r odes m ust be issued in sm all quant it ies and t he
exposur e t im e lim it ed; heat ed ‘quivers’ facilit at e t his cont r ol.
Flux- cored wire spools t hat are not seam less should be cover ed or r et urned
t o a suit able st orage condit ion when not in use.
Basic agglom erat ed SAW fluxes should be ret urned t o t he heat ed silo when
welding is not cont inuous.
Check t he am ount of m oist ure present in t he shielding gas by checking t he
dew point ( m ust be bellow - 60°C) .
Ensuring t hat t he weld zone is dr y and free fr om rust / scale and oil/ grease.
Te nsile st r e ss
Ther e are always t ensile st resses act ing on a weld because t her e ar e always
residual st resses fr om w elding.
The m agnit ude of t he t ensile st resses is m ainly dependent on t he t hickness of
t he st eel at t he j oint , heat input , j oint t ype, and size and weight of t he
com ponent s being welded.
Tensile st resses in highly r est rained j oint s m ay be as high as t he yield st rengt h
of t he st eel and t his is usually t he case in large com ponent s wit h t hick j oint s
and it is not a fact or t hat can easily be cont r olled.
The only pract ical ways of reducing t he influence of residual st resses m ay be
by:





Avoiding st ress concent rat ions due t o poor fit - up.
Avoiding poor weld profile ( sharp w eld t oes) .
Applying a st ress- r elief heat t r eat m ent aft er w elding.
I ncreasing t he t rav el speed as pract icable in order t o reduce t he heat input .
Keeping weld m et al volum e t o an as low lev el as possible.
These m easur es ar e part icularly im port ant when welding som e low alloy st eels
t hat have part icularly sensit ivit y t o hydrogen cr acking.
WI S10- 30816
Weldabilit y of St eels
11-3
Copyright © TWI Lt d
Susce pt ible H AZ m icr ost r uct ur e
A suscept ible HAZ m icr ost ruct ure is one t hat cont ains a relat ively high
proport ion of hard brit t le phases of st eel - part icularly m art ensit e.
The HAZ hardness is a good indicat or of suscept ibilit y and when it exceeds a
cert ain value a part icular st eel is consider ed t o be suscept ible. For C and C- Mn
st eels t his hardness value is ~ 350HV and suscept ibilit y t o H cracking increases
as hardness increases above t his value.
The m axim um hardness of an HAZ is influenced by:


Chem ical com posit ion of t he st eel.
Cooling rat e of t he HAZ aft er each w eld run is m ade.
For C and C- Mn st eels a form ula has been developed t o assess how t he
chem ical com posit ion will influence t he t endency for significant HAZ hardening t he carbon equivalent value ( CEV) form ula.
The CEV form ula m ost widely used ( and adopt ed by I I W) is:
CEV iiw
=
% C + % Mn + % Cr + % Mo + % V
6
5
+ % Ni + % Cu
15
The CEV of a st eel is calculat ed by insert ing t he m at erial t est cert ificat e values
shown for chem ical com posit ion int o t he form ula. The higher t he CEV of a st eel
t he great er it s suscept ibilit y t o HAZ hardening and t herefor e t he gr eat er t he
suscept ibilit y t o H cracking.
The elem ent wit h m ost influence on HAZ hardness is carbon. The fast er t he rat e
of HAZ cooling aft er each weld run, t he great er t he t endency for hardening.
Cooling rat e t ends t o incr ease as:


Heat input decr eases ( lower energy input ) .
Joint t hickness increases ( bigger heat sink) .
Avoiding a suscept ible HAZ m icrost ruct ure ( for C and C- Mn st eels) requires:



Procuring st eel wit h a CEV t hat is at t he low- end of t he range for t he st eel
grade( lim it ed scope of effect iveness) .
Using m oderat e w elding heat input so t hat t he w eld does not cool quickly
( and give HAZ hardening) .
Applying pre- heat so t hat t he HAZ cools m or e slowly ( and does not show
significant HAZ hardening) ; in m ult i- run welds, m aint ain a specific int erpass
t em perat ur e.
For low alloy st eels, wit h addit ions of elem ent s such as Cr, Mo and V, t he CEV
for m ula is not applicable and so m ust not be used t o j udge t he suscept ibilit y t o
hardening. The HAZ of t hese st eels will always t end t o be relat ively hard
regardless of heat input and pre- heat and so t his is a ‘fact or’ t hat cannot be
effect ively cont r olled t o reduce t he risk of H cracking. This is t he reason why
som e of t he low alloy st eels have great er t endency t o show hydr ogen cracking
t han in weldable C and C- Mn st eels, which enable HAZ hardness t o be
cont r olled.
WI S10- 30816
Weldabilit y of St eels
11-4
Copyright © TWI Lt d
W e ldm e n t a t low t e m pe r a t u r e
Weldm ent t em perat ur e has a m aj or influence on
m ainly by influencing t he rat e at which H can m ov e
and HAZ. While a weld is r elat ively warm ( > ~ 300°C)
and escape int o t he at m ospher e rat her t han
em brit t lem ent .
suscept ibilit y t o cracking
( diffuse) t hr ough t he weld
H will diffuse quit e rapidly
be t rapped and cause
Reducing t he influence of low weldm ent t em per at ure ( and t he risk of t r apping H
in t he weldm ent ) can be effect ed by:



Applying a suit able pre- heat t em perat ur e ( t ypically 50 t o ~ 250°C) .
Prevent ing t he weld from cooling down quickly aft er each pass by
m aint aining t he preheat and t he specific int erpass t em perat ure during
welding.
Maint aining t he pre- heat t em per at ure ( or r aising it t o ~ 250°C) when
welding has finished and holding t he j oint at t his t em perat ur e for a num ber
of hours ( m inim um 2) t o facilit at e t he escape of H ( called post - he a t * ) .
* Post - heat m ust not
t em perat ur e ~ 600°C.
1 1 .2 .4
be confused wit h PWHT which is perform ed at
a
H ydr oge n cr a ck in g in w e ld m e t a l
Hydr ogen cracks can form in st eel weld m et al under cert ain circum st ances. The
m echanism of cracking, and ident ificat ion of all t he influencing fact ors, is less
clearly underst ood t han for HAZ cracking but it can occur when welding
condit ions cause H t o becom e t rapped in weld m et al rat her t han in HAZ.
How ev er it is recognised t hat w elds in higher st r engt h m at erials, t hicker
sect ions and using large beads ar e t he m ost com m on ar eas wher e problem s
arise.
Hydr ogen cracks in weld m et al usually lie at 45° t o t he direct ion of principal
t ensile st r ess in t he weld m et al and t his is usually t he longit udinal axis of t he
weld ( Figure 11.3) . I n som e cases t he cracks are of a V form at ion, hence an
alt ernat ive nam e chevr on cracking.
Ther e are not any well- defined rules for avoiding weld m et al hydrogen crack s
apart from :


Ensur e a low hydr ogen welding process is used.
Apply preheat and m aint ain a specific int erpass t em perat ur e.
BS EN 1011- 2 ent it led Welding – Recom m endat ions for welding of m et allic
m at erials – Part 2: Ar c w elding of ferrit ic st eels gives in Annex C pract ical
guidelines about how t o avoid H cracking. Pract ical cont rols are based
principally on t he applicat ion of pre- heat and cont r ol of pot ent ial H associat ed
wit h t he welding process.
1 1 .3
Solidif ica t ion cr a ck in g
The t echnically cor rect nam e for crack s t hat form during weld m et al
solidificat ion is solidificat ion cracks but ot her nam es ar e som et im es used when
referring t o t his t ype of cracking.



Hot cracking - t hey occur at high t em perat ur es – while t he w eld is hot .
Cent r eline cracking - crack s m ay appear dow n t he cent reline of t he weld
bead.
Crat er cracking - sm all cracks in weld crat er s are solidificat ion cracks.
WI S10- 30816
Weldabilit y of St eels
11-5
Copyright © TWI Lt d
Because a w eld m et al m ay be part icularly suscept ible t o solidificat ion cracking it
m ay be said t o show hot short ness because it is short of duct ilit y when hot and
so t ends t o crack.
Figure 11.4 shows a t ransv er se sect ion of a weld wit h a t ypical cent reline
solidificat ion crack .
1 1 .3 .1
Fa ct or s inf lu e ncing susce pt ibilit y t o solidif ica t ion cr a ck ing
Solidificat ion cracking occur s when t hree condit ions exist at t he sam e t im e:



1 1 .3 .2
Weld m et al has a suscept ible chem ical com posit ion.
Welding condit ions used give an unfavour able bead shape.
High level of r est raint or t ensile st resses present in t he weld area.
Cr a ck ing m e ch a nism
All weld m et als solidify ov er a t em per at ure range and since solidificat ion st art s
at t he fusion line t owar ds t he cent reline of t he weld pool, during t he last st ages
of weld bead solidificat ion t here m ay be enough liquid present t o form a w eak
zone in t he cent re of t he bead. This liquid film is t he r esult of low m elt ing point
const it uent s being pushed ahead of t he solidificat ion front .
During solidificat ion, t ensile st resses st art t o build- up due t o cont ract ion of t he
solid part s of t he weld bead, and it is t hese st resses t hat can cause t he weld
bead t o rupt ur e. These circum st ances result in a weld bead showing a
cent r eline crack t hat is present as soon as t he bead has been deposit ed.
Cent r eline solidificat ion cracks t end t o be sur face breaking at som e point in
t heir lengt h and can be easily seen during visual inspect ion because t hey t end
t o be r elat ively wide cracks.
1 1 .3 .3
Avoiding solidif ica t ion cr a ck ing
Avoiding solidificat ion cracking requires t he influence of one of t he fact or s
responsible, t o be r educed t o an inact ive level.
W e ld m e t a l com posit ion
Most C and C- Mn st eel weld m et als m ade by m odern st eelm aking m et hods do
not have chem ical com posit ions t hat are part icularly sensit ive t o solidificat ion
cracking.
How ev er, t hese weld m et als can becom e sensit ive t o t his t ype of cracking if
t hey are cont am inat ed wit h elem ent s, or com pounds, t hat produce relat ively
low m elt ing point film s in weld m et al.
Sulphur and copper ar e elem ent s t hat can m ake st eel weld m et al sensit ive t o
solidificat ion cracking if t hey are pr esent in t he w eld at relat ively high levels.
Sulphur cont am inat ion m ay lead t o t he form at ion of iron sulphides t hat rem ain
liquid when t he bead has cooled down as low as ~ 980°C, whereas bead
solidificat ion st art s at above 1400°C.
The source of sulphur m ay be cont am inat ion by oil or grease or it could be
picked up from t he less refined parent st eel being welded by dilut ion int o t he
weld.
Copper cont am inat ion in weld m et al can be sim ilarly harm ful because it has low
solubilit y in st eel and can for m film s t hat are st ill m olt en at ~ 1100°C.
WI S10- 30816
Weldabilit y of St eels
11-6
Copyright © TWI Lt d
Avoiding solidificat ion cracking ( of an ot herwise non- sensit ive weld m et al)
requires t he avoidance of cont am inat ion wit h pot ent ially harm ful m at erials by
ensuring:


Weld j oint s are t horoughly cleaned im m ediat ely befor e w elding.
Any copper cont aining welding accessories ar e suit able/ in suit able condit ion
- such as backing- bars and cont act t ips used for GMAW, FCAW and SAW.
Unf a vour a ble w e ldin g con dit ion s
Unfavourable welding condit ions are t hose t hat encour age w eld beads t o solidify
so t hat low m elt ing point film s becom e t rapped at t he cent r e of a solidifying
weld bead and becom e t he weak zones for easy crack form at ion.
Figure 11.5 show s a w eld bead t hat has solidified using unfavourable welding
condit ions associat ed wit h cent r eline solidificat ion cracking.
The weld bead has a cr oss- sect ion t hat is quit e deep and narr ow – a widt h- t odept h rat io < ~ 2 and t he solidifying dendrit es have pushed t he lower m elt ing
point liquid t o t he cent re of t he bead wher e it has becom e t rapped. Since t he
surr ounding m at erial is shrinking as a result of cooling, t his film would be
subj ect ed t o t ensile st ress, which leads t o cracking.
I n cont rast , Figure 11.6 shows a bead t hat has a widt h- t o- dept h rat io t hat is
> > 2. This bead shape shows lower m elt ing point liquid pushed ahead of t he
solidifying dendrit es but it does not becom e t r apped at t he bead cent re. Thus,
ev en under t ensile st r esses r esult ing from cooling, t his film is self- healing and
cracking is avoided.
SAW and spray- t ransfer GMAW ar e m or e likely t o give weld beads wit h an
unfavourable widt h- t o- dept h rat io t han t he ot her ar c w elding processes. Also,
elect r on beam and laser welding processes ar e ext r em ely sensit ive t o t his kind
of cracking as a r esult of t he deep, nar row beads pr oduced.
Avoiding unfavourable welding condit ions t hat lead t o cent reline solidificat ion
cracking ( of weld m et als wit h sensit ive com posit ions) m ay require significant
changes t o w elding param et ers, such as reducing t he:


Welding curr ent ( t o give a shallower bead) .
Welding speed ( t o give a wider w eld bead) .
Avoiding unfavourable welding condit ions t hat lead t o crat er cracking of a
sensit ive weld m et al requires changes t o t he t echnique used at t he end of a
weld when t he arc is ex t inguished, such as:



For TI G w elding, use a curr ent slope- out device so t hat t he cur rent , and
weld pool dept h gradually reduce before t he arc is ext inguished ( gives m or e
favourable weld bead widt h- t o- dept h rat io) . I t is also a com m on pract ice t o
backt rack t he bead slight ly befor e br eaking t he ar c or lengt hen t he arc
gradually t o avoid crat er cracks.
For TI G w elding, m odify weld pool solidificat ion m ode by feeding t he filler
wire int o t he pool unt il solidificat ion is alm ost com plet e and av oiding a
concave cr at er.
For MMA, m odify t he weld pool solidificat ion m ode by reversing t he direct ion
of t rav el at t he end of t he w eld run so t hat crat er is filled.
WI S10- 30816
Weldabilit y of St eels
11-7
Copyright © TWI Lt d
1 1 .4
La m e lla r t e a r ing
Lam ellar t earing is a t ype of cracking t hat only occurs in st eel plat e or ot her
rolled product s underneat h a weld.
Charact erist ics of lam ellar t earing are:




Cracks only occur in t he r olle d pr oduct s eg plat e and sect ions.
Most com m on in C- Mn st eels.
Cracks usually form close t o, but j ust out side, t he HAZ.
Cracks t end t o lie parallel t o surface of t he m at erial ( and t he fusion
boundary of t he w eld) , having a st epped aspect .
The abov e charact erist ics can be seen in Figure 11.7a.
1 1 .4 .1
Fa ct or s inf lu e ncing susce pt ibilit y t o la m e lla r t e a r ing
Lam ellar t earing occur s when t wo condit ions exist at t he sam e t im e:


A suscept ible rolled plat e is used t o m ake a w eld j oint .
High st resses act in t he t hrough- t hickness direct ion of t he suscept ible
m at erial ( known as t he short - t ransv er se direct ion) .
Susce pt ible r olle d pla t e
A m at erial t hat is suscept ible t o lam ellar t earing has very low duct ilit y in t he
t hrough- t hickness direct ion ( short - t ransv er se direct ion) and is only able t o
accom m odat e t he r esidual st resses fr om welding by t earing rat her t han by
plast ic st raining.
Low t hr ough- t hickness duct ilit y in rolled product s is caused by t he pr esence of
num erous non- m et allic inclusions in t he for m of elongat ed st ringer s. The
inclusions form in t he ingot but are flat t ened and elongat ed during hot rolling of
t he m at erial.
Non- m et allic inclusions associat ed wit h lam ellar
m anganese sulphides and m anganese silicat es.
t earing
ar e
principally
H igh t hr ough- t hick ne ss st r e ss
Weld j oint s t hat are T, K and Y configurat ions end up w it h a t e n sile r e sidu a l
st r e ss com pone nt in t he t hr ough- t hick n e ss dir e ct ion .
The m agnit ude of t he t hrough- t hickness st r ess increases as t he rest raint
( rigidit y) of t he j oint increases. Sect ion t hickness and size of weld are t he m ain
influencing fact ors and it is in t hick sect ion, full penet rat ion T, K and Y j oint s
t hat lam ellar t earing is m or e likely t o occur.
1 1 .4 .2
Cr a ck ing m e ch a nism
High st resses in t he t hrough- t hickness direct ion, t hat are pr esent as welding
residual st resses, because t he inclusion st ringer s t o open- up ( de- cohese) and
t he t hin ligam ent s bet ween individual de- cohesed inclusions t hen t ear and
produce a st epped crack.
Figure 11.11b show s a t ypical st ep- like lam ellar t ear .
WI S10- 30816
Weldabilit y of St eels
11-8
Copyright © TWI Lt d
1 1 .4 .3
Avoiding la m e lla r t e a r in g
Lam ellar t earing can be av oided by r educing t he influence of one, or bot h, of
t he fact or s.
Susce pt ible r olle d pla t e
BSEN 10164 ( St eel product s wit h im prov ed deform at ion propert ies
perpendicular t o t he surface of t he pr oduct – Technical delivery condit ions)
gives guidance on t he procur em ent of plat e t o r esist lam ellar t earing.
Resist ance t o lam ellar t earing can be evaluat ed by m eans of t ensile t est pieces
t aken wit h t heir axes perpendicular t o t he plat e surface ( t he t hr ough- t hickness
direct ion) . Through- t hickness duct ilit y is m easured as t he % r educt ion of ar ea
( % R of A) at t he point of fr act ur e of t he t ensile t est piece ( Figure 11.8) .
The great er t he m easured % R of A, t he gr eat er t he resist ance t o lam ellar
t earing. Values in excess of ~ 20% indicat e good resist ance even in very highly
const rained j oint s.
Reducing t he suscept ibilit y of rolled plat e t o lam ellar t earing can be achiev ed by
ensuring t hat it has good t hrough- t hickness duct ilit y by:


Using clean st eel t hat has low sulphur cont ent ( < ~ 0.015% ) and
consequent ly has r elat ively few inclusions.
Procuring st eel plat e t hat has been subj ect ed t o t hr ough- t hickness t ensile
t est ing t o dem onst rat e good t hr ough- t hickness duct ilit y ( as EN 10164) .
Thr ough - t h ick ne ss st r e ss
Through t hickness st r ess in T, K and Y j oint s is principally t he residual st ress
from w elding, alt hough t he addit ional service st ress m ay hav e som e influence.
Reducing t he m agnit ude of t hr ough- t hickness st resses for a part icular weld j oint
would require m odificat ion t o t he j oint , in som e way and so m ay not always be
pract ical because of t he need t o sat isfy design requirem ent s. Howev er, m et hods
t hat could be considered are:





Reducing t he size of t he weld by:
Using a part ial penet rat ion but t weld inst ead of full- penet rat ion.
Using fillet welds inst ead of a full, or a part ial pen but t weld ( Figure 11.8) .
By applying a but t ering layer of weld m et al t o t he surface of a suscept ible
plat e so t hat t he highest t hr ough- t hickness st rain is locat ed in t he weld
m et al and not t he suscept ible plat e ( Figure 11.9) .
Changing t he j oint design – such as using a for ged or ext ruded int erm ediat e
piece so t hat t he suscept ible plat e does not experience t hrough- t hickness
st ress ( Figure 11.10) .
WI S10- 30816
Weldabilit y of St eels
11-9
Copyright © TWI Lt d
Figur e 1 1 .1 Typica l loca t ions of hydr oge n indu ce d cold cr a ck s.
Figur e 1 1 .2 H ydr oge n induce d cold cr a ck t ha t init ia t e d t he H AZ a t t he t oe of a
fille t w e ld.
WI S10- 30816
Weldabilit y of St eels
11-10
Copyright © TWI Lt d
X
Transverse
cracks
a
Y
Weld layers w it h
cracks lying at
45° t o X - Y axis
b
Figur e 1 1 .2 a a n d b
a
b
Pla n vie w of a pla t e but t w e ld show ing subsur f a ce t r a nsve r se cr a ck s;
Longit u dina l se ct ion X- Y of t he a bove w e ld show in g how t he t r a nsve r se
cr a ck s a ct ua lly lie a t 4 5 ° t o t he sur fa ce . The y t e n d t o r e m a in w it hin a n
individua l w e ld r u n a n d m a y be in w e ld se ve r a l la ye r s. The ir a ppe a r a n ce in
t his or ie nt a t ion ha s give n r ise t o t he n a m e ‘ch e vr on’ cr a ck s ( a r r ow sha pe d
cr a ck s) .
WI S10- 30816
Weldabilit y of St eels
11-11
Copyright © TWI Lt d
a
b
Figur e 1 1 .3
a
b
Solidifica t ion cr a ck a t t he w e ld be a n ce nt r e w he r e colum na r de ndr it e s ha ve
t r a ppe d som e low e r m e lt ing poin t liquid
The w e ld be a d doe s n ot ha ve a n ide a l sha pe bu t it ha s solidifie d w it hout t he
de ndr it e s m e e t ing ‘e nd- on’ a nd t r a pping low e r m e lt ing point liquid t h e r e by
r e sist ing solidifica t ion cr a ck ing.
WI S10- 30816
Weldabilit y of St eels
11-12
Copyright © TWI Lt d
W
D
W/ D < 2
Direction of travel
Figur e 1 1 .4 A w e ld be a d w it h a n unfa vou r a ble w idt h- t o- de pt h r a t io.
This is responsible for liquid m et al being pushed int o t he cent re of t he bead by
t he advancing colum nar dendrit es and becom ing t he weak zone t hat is
rupt ured.
W
W/ D > ~ 2
D
Direction of travel
Figur e 1 1 .5 W e ld be a d w it h a fa vour a ble w idt h - t o- de pt h r a t io.
The dendrit es push t he lowest m elt ing point m et al t owards t he surface at t he
cent r e of t he bead cent r e and so it does not for m a w eak cent ral zone.
WI S10- 30816
Weldabilit y of St eels
11-13
Copyright © TWI Lt d
Fusion
boundar
HAZ
a
Crack pr opagat ion by t earing
of ligam ent s bet ween
‘de- cohesed’ inclusion st ringers
De- cohesion of
inclusion st ringers
Through- t hickness
residual st resses
from w elding
I nclusion
st ringer
b
Figur e 1 1 .6
a
b
Typica l la m e lla r t e a r loca t e d j ust out side t he visible H AZ;
St e p- lik e cr a ck cha r a ct e r ist ic of a la m e lla r t e a r .
WI S10- 30816
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Through- t hickness
t ensile t est piece
Plat e surface
Reduct ion of diam et er
at point of fr act ur e
Plat e surface
Figur e 1 1 .7 Roun d t e nsile t e st pie ce t a k e n w it h it s a x is in t he shor t - t r a nsve r se
dir e ct ion ( t hr ou gh t hick ne ss of pla t e ) t o m e a su r e t he % R. of A. a nd a sse ss t he
pla t e ’s r e sist a nce t o la m e lla r t e a r ing.
Suscept ible plat e
Suscept ible plat e
Figur e 1 1 .8 Re ducin g t he e ffe ct ive siz e of a w e ld w ill r e duce t he t hr ought hick ne ss st r e ss on t he su sce pt ible pla t e a n d m a y be sufficie nt t o r e duce t he
r isk of la m e lla r t e a r ing.
WI S10- 30816
Weldabilit y of St eels
11-15
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Suscept ible plat e
Ext ruded sect ion
Figur e 1 1 .9 La m e lla r t e a r ing ca n be a voide d by cha ngin g t he j oint de sign.
Weld m et al ‘but t ering’
Suscept ible plat e
Figur e 1 1 .1 0 Tw o la ye r s of w e ld m e t a l ( usua lly by M M A) a pplie d t o susce pt ible
pla t e be for e t he T- but t w e ld is m a de .
WI S10- 30816
Weldabilit y of St eels
11-16
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Weldability of Steels
Section 11
Copyright © TWI Ltd
Copyright © TWI Ltd
What is Weldability?
"The ease with which a material, or materials
can be welded to give an acceptable joint"
Weldability Problems
Weldability can pose problems for welders,
inspectors & engineers.
BS 499 - 1
Weldability = hardenability = susceptibility to
cracking
Weldability is a measure of how easy (or
how difficulty) it is to:
1. Obtain crack free welds.
2. Achieve adequate mechanical properties.
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Copyright © TWI Ltd
Weldability Problems
Weldability problems can be overcome through
understanding
 In order to produce a sound weld it is
necessary to know and understand the
material properties of the steels to be welded.
Weldability
Weldability is the key to successful welding
Weldability
Weld process
crack
mechanisms
Effect of
carbon
Grain
structures
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Copyright © TWI Ltd
11‐1
The Effect of Carbon
Steel is an alloy of iron and carbon
(0.01 - 1.4%C). Plain Carbon Steels
The effect of carbon
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Copyright © TWI Ltd
Carbon - The Key Element in Steel
The Effect of Carbon
It affects
Increase in tensile strength
1. Strength.
Increase in hardness
2. Hardness.
0.1% Increase in carbon
1.4%
3. Ductility.
Decrease in elongation
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Copyright © TWI Ltd
The Effect of Carbon
Steel alloys can be divided into five main
groups
1.
2.
3.
4.
5.
Carbon steels.
Alloy steels.
Quenched & tempered steels.
Heat treatable low alloy steels.
Chromium molybdenum steels.
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The Effect of Carbon
Plain carbon steels come in three types
Low Carbon Steels
0.01 - 0.3%C
Medium Carbon Steels
0.3 - 0.6%C
High Carbon Steels
0.6 - 1.4%C
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11‐2
Alloy Steels
Alloy steels contain iron and carbon plus other
alloying elements to give the steel required
mechanical & metallurgical properties.
Low alloy steels
Fe & C +Mn, Cr, Ni, Mo < 7% total
Elements in steels
High alloy steels
Fe & C + Mn, Cr, Ni, Mo> 7% total
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Alloying Elements
Manganese (Mn) - Primary desulphuriser &
secondary deoxidizer.
 Added to steels to reduce carbon.
 Affects strength & hardenability.
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Alloying Elements
Molybdenum (Mo) - Improves creep resistance
and temper embrittlement.
Chromium (Cr) - Improves hardness &
resistance to wear. A major element in stainless
steels to give corrosion resistance.
Silicon (Si) - Primary deoxidizer.
Nickel (Ni) - Improves ductility, strength &
toughness. A key element in austenitic stainless
steel to improve corrosion resistance from acids.
Aluminium (Al) - Grain refiner & tertiary
deoxidizer.
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Alloying Elements
Sulphur (S) - An impurity in steels.
Harm full because it can cause ‘hot shortness’ cracking during hot working.
Phosphorus (P) - An impurity in steels.
Harmful in steels when over 0.05% because it
can cause ‘cold shortness’ - cracking during cold
working.
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Copyright © TWI Ltd
Carbon Content Vs Carbon Equivalent
Carbon content
The actual amount of carbon in the steel.
Carbon Equivalent
The carbon content in relation to other alloying
elements.
Ceq% = C + Mn + Cr + Mo + V + Cu + Ni
6
5
15
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11‐3
Carbon Content Vs Carbon Equivalent
Carbon Content Vs Carbon Equivalent
Because Manganese has 1/6 of the effect on
hardenability compared to one part Carbon.
A steel contains 0.12%C and 1.3%Mn.
 The formula can be shortened to:
What is the carbon equivalent?
Ceq% = C + Mn
6
= 0.12 + 1.3
6
= 0.12 + 0.216
Ceq% = C + Mn
6
Ceq = 0.336%
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Grain Structures
Grain structures in materials are influenced
by
1. Elements in the material.
2. Temperature.
3. Cooling rate.
Key grain structures
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Copyright © TWI Ltd
Simplified Continuous
Cooling Diagram
Critical Cooling Rate
Austenite
Temperature
Critical cooling rate
The rate of cooling from the austenite region
which determines the final grain structure.
Martensite Bainite
Ferrite + Pearlite
Time
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Copyright © TWI Ltd
11‐4
Weld Process Crack Mechanisms
TWI – Welding Inspection
1. Hydrogen induced cold cracking (HICC).
2. Solidification cracking.
3. Lamellar tearing.
4. Re-heat cracking.
Hydrogen Induced Cold Cracking (HICC)
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Copyright © TWI Ltd
Factors for HICC
Hydrogen
Why can Hydrogen be a problem?
Tensile stress
It can cause embrittlement in steel.
Susceptible
microstructure
Cracking
(at room
temperature)
This is the process by which steels become
brittle and fractures due to the introduction and
subsequent diffusion of hydrogen into the metal.
High hydrogen
concentration
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Copyright © TWI Ltd
Factors Affecting HICC
Factor
H2 Access into Weld
Quantum
Diffusible
> 15ml/100gm. Of weld metal
hydrogen content for C steels. Can reduce with
higher strength levels
Stress
> 0.5 of yield strength
Temperature
< 300C
Susceptible
microstructure
Hardness > 400 VPN
Water vapour in
the air or in the
shielding gas
H2
Moisture on
the electrode
or grease on
the wire
H2
H
Oxide or
grease on
the plate
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H
H
H2
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11‐5
The Process of HICC
Hydrogen enters the weld via the welding arc.
Heat of the arc breaks down molecular hydrogen
(H2) into atomic hydrogen (H).
As weld cools hydrogen diffuses outwards into
parent plate and atmosphere.
The Process of HICC
As the weld cools some hydrogen atoms can
become trapped between grain boundaries as
the lattice structure of the steel also contracts
and changes.
Below 300°C hydrogen prefers to be in its
molecular form (H2) so individual atoms are
attracted towards each other.
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Copyright © TWI Ltd
The Process of HICC
The Process of HICC
Atomic
Hydrogen
(H)
Steel in expanded condition
Hydrogen
diffusion
Above 300oC
Molecular
Hydrogen
(H2)
Steel in expanded condition
Above
300oC
Steel under contraction
Below 300oC
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Copyright © TWI Ltd
The Process of HICC
Avoidance of HICC
When hydrogen molecules exist in large numbers
a lot of pressure is exerted, typically between
400 to 1400N/mm².
1. Clean joint preparations.
This can lead to cracking in susceptible
microstructures where ductility is poor.
3. Use a low hydrogen welding process.
2. Pre heat.
4. Use a multi pass welding technique.
5. Delay cooling rate.
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Copyright © TWI Ltd
11‐6
Avoidance of HICC
Avoidance of HICC
Below is a list of welding process in order of
lowest hydrogen content (H2/100 grams of
deposited weld metal).
Below is a list of hydrogen scales taken from BS
EN 1011 with regards to 100 grams of weld
metal deposited.
TIG
MIG/MAG
MMA
SAW
FCAW
Scale
Hydrogen Content
A
> 15 ml
<
<
<
<
<
3ml
5ml
5ml  60ml
10ml
15ml
B
> 10 ml
< 15 ml
C
> 5 ml
< 10 ml
D
> 3 ml
< 5 ml
E
< 3 ml
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Copyright © TWI Ltd
Avoiding HICC
Factor
Avoiding them
Diffusible
hydrogen
Use LH consumable, process; cleaning;
conditioning of consumables; weather
conditions; use post heating; PWHT
Susceptible
microstructure
Use preheat
Temperature
Maintain preheat, Use post heat
Stress
Reduce weld volume; balanced
welding; skip, back step welding; presetting; automate; reduce number of
runs; large weld beads; PWHT
TWI - Welding Inspection
Solidification (hot) cracking
Solidification (Hot) Cracking
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Solidification (Hot) Cracking
Only occur in the weld
metal.
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Factors for Solidification Cracking
1. High tensile stresses.
2. Sulphur.
Appear as straight
lines along the centre
line of the weld.
3. Joint geometry.
Can occur in the weld
crater (star crack).
Usually readily visible.
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11‐7
Solidification Cracking
 Sulphur in the parent material may dilute in the
weld metal to form iron sulphides (low strength,
low melting point compounds).
 During weld metal solidification, columnar crystals
push still liquid iron sulphides in front to the last
place of solidification, weld centerline .
 The bonding between the grains which are
themselves under great stress. may now be very
poor to maintain cohesion and a crack will result,
weld centerline.
Solidification Cracking
Factors for solidification cracking
 Columnar grain growth with impurities in weld
metal (sulphur, phosphorus and carbon).
 The amount of stress/restraint.
 Joint design high depth to width ratios.
 Liquid iron sulphides are formed around solidifying
grains.
 High contractional strains are present.
 High dilution processes are being used.
 There is a high carbon content in the weld metal.
 Most commonly occurring in sub-arc welded joints.
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Copyright © TWI Ltd
Solidification Cracking in Fe Steels
Liquid Iron Sulphide films
Solidification crack
*
Contractional
strain
Solidification Cracking
Columnar
grains
Intergranular liquid
film
Columnar
HAZ
grains
Shallow, wider weld
bead
Deep, narrower weld
bead
On solidification the
bonding between the
grains may be adequate
to maintain cohesion and
a crack is unlikely to
occur
On solidification the
bonding between the
grains may now be very
poor to maintain cohesion
and a crack may result.
Avoid > than 2:1 ratio
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Copyright © TWI Ltd
Solidification Cracking
Solidification Cracking
Precautions for controlling solidification cracking
 The use of high manganese and low carbon
content fillers.
 Minimise the amount of stress/restraint acting on
the joint during welding.
 The use of high quality parent materials, low
levels of impurities (phosphorus and sulphur).
 Clean joint preparations contaminants (oil,
grease, paints and any other sulphur containing
product).
 Joint design selection depth to width ratios, avoid
>2:1 ratio
 Avoid high welding speeds.
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HAZ
Add Manganese to weld
metal
Spherical Mn Sulphide
balls form between
solidified grains
Cohesion and strength
between grains remains
Contractional
strain
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11‐8
TWI – Welding Inspection
Lamellar Tearing
 Location: Parent metal just below the HAZ.
 Steel Type: Any steel type possible.
 Susceptible Microstructure: Poor through thickness
ductility.
 Lamellar tearing has a step like appearance due to the
solid inclusions in the parent material (eg sulphides and
silicates) linking up under the influence of welding
stresses.
 Low ductile materials (often related to thickness) in the
short transverse direction containing high levels of
impurities are very susceptible to lamellar tearing.
 It forms when the welding stresses act in the short
transverse direction of the material (through thickness
direction).
Lamellar Tearing
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Copyright © TWI Ltd
Lamellar Tearing
Lamellar Tearing
Susceptible joint types
Step like appearance
Tee fillet weld
Corner butt weld
(single-bevel)
Tee butt weld
(double-bevel)
Cross section
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Lamellar Tearing
Critical area
Critical area
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Lamellar Tearing
Factors for lamellar tearing to occur
 Low quality parent materials, high levels of
impurities there is a high sulfur content in the base
metal.
 Joint design, direction of stress 90 degrees to the
rolling direction, the level of stress acting across
the joint during welding.
 Note! very susceptible joints may form lamellar
tearing under very low levels of stress.
 High contractional strains are through the short
transverse direction.
 There is low through thickness ductility in the base
metal.
 There is high restraint on the work.
Critical
area
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Copyright © TWI Ltd
11‐9
Lamellar Tearing
Assessment of susceptibility to lamellar
tearing:
 Carry out through thickness tensile test.
 Carry out cruciform welded tensile test.
Lamellar Tearing
Precautions for controlling lamellar tearing
 The use of high quality parent materials, low levels of
impurities.
 The use of buttering runs.
 A gap can be left between the horizontal and vertical
members enabling the contraction movement to take
place.
 Joint design selection.
 Minimise the amount of stress/restraint acting on the
joint during welding.
 Hydrogen precautions.
Copyright © TWI Ltd
Copyright © TWI Ltd
Lamellar Tearing
Short Tensile (Through Thickness) Test
The short tensile test or through thickness test is a test to
determine a materials susceptibility to lamellar tearing
Friction welded
extension stubs
Plate Material
Short Tensile Specimen
Sample of
Parent Material
6.4mm
DIA
Final short transverse
tensile specimen
Methods of avoiding lamellar
tearing:*
1
Avoid restraint*.
2
Use controlled low sulfur plate*.
3
Grind out surface and butter*.
4
Change joint design*.
5
Use a forged T piece (critical
applications)*.
The results are given as a STRA va
Short Transverse Reduction in Are
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Copyright © TWI Ltd
Lamellar Tearing
Modifying a Tee joint to avoid lamellar tearing
Non-susceptible
Susceptible
Improved
Lamellar Tearing
Modifying a corner joint to avoid lamellar tearing
Susceptible
Non-Susceptible
Susceptible
Non-susceptible
Use a forged Tee
piece
Susceptible Less susceptible
Prior buttering of the joint
with a ductile layer of weld
metal may avoid lamellar
tearing
Copyright © TWI Ltd
An open corner joint
may be selected to
avoid lamellar
tearing
Copyright © TWI Ltd
11‐10
STRA Test
Probable freedom from
tearing in any joint type
STRA %
Reduction
of CSA
20
Some risk in highly restrained
joints eg node joint, joints
between sub-fabs
15
Some risk in moderately
restrained joints eg box
columns
10
Some risk in lightly restrained
joints T-joints eg I-beams
Copyright © TWI Ltd
Question 1
One of your inspectors suggests to you that
lamellar tearing may have occurred in a single
bevel butt joint. Would you agree with this
comment?
a. No, this defect can only occur in single v butt
welds
b. No, this type of defect will only occur in C/Mn
steels with a CE value >0.48%
c. Yes, this defect is possible in a single bevel
butt, but it would require RT for clarification
d. All options are incorrect
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Question 3
One of your inspectors suggests to you that the pre heat
temperatures are too low to prevent hydrogen cracking
occurring. Which of the following combinations are correct
for determining a correct pre heat temperature to be
applied prior to welding?
a. Material thickness, joint design, the amount of
hydrogen and welding process
b. Material thickness, the amount of stress, hydrogen
content and material type
c. Material type and thickness, hydrogen scale and heat
input
d. The amount of stress, welding process, hydrogen
content and material type
Copyright © TWI Ltd
Weldability
You are working as a Senior Welding Inspector
during the fabrication and welding of a top side
module, the module is fabricated from C/Mn
steel maximum CE value of 0.46%.
Certain sections are fabricated from universal
beams with thicknesses ranging from 12.5 to
50mm thickness, other sections are fabricated
from steel plate again ranging from 12.5 mm to
50mm thickness.
Copyright © TWI Ltd
Question 2
You notice from the WPS on certain joints a pre heat of
150°C is required, on other joints the preheat is only
75°C. Why do you think some joints require more pre heat
than others?
a. This would be due to the different thickness of
materials being used and the increased chances of
solidification cracking
b. This would be due to the different thickness of
materials being used and the increased chances of
hydrogen cracking
c. This would be due to the fact that some welders
require more preheat than others as it increases
penetration
d. All options are incorrect; it’s due to lamellar tearing in
thicker materials
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Question 4
One of your inspectors asks you what are the
main factors affecting hydrogen cracking. Which
of the following would be your best reply?
a. Temperature, the amount of stress, molecular
hydrogen and material composition
b. Material thickness, atomic hydrogen, material
composition and the amount of stress
c. Sulphur content >0.03%, hydrogen content >
15ml, the amount of stress and material
composition
d. All options have insufficient information given
Copyright © TWI Ltd
11‐11
Question 5
During visual inspection one of your inspectors
detects a longitudinal crack along the weld
centerline approximately 100mm in length.
Which of the following would be reasons for the
occurrence of this type of crack?
a. Sulphur contents and manganese contents
too low
b. Sulphur contents too high, manganese
contents too low
c. Sulphur contents too low, manganese
contents too high
d. All options would cause this type of cracking
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Question 7
When inspecting the material certificates you notice
some of the materials are classified as Z steels.
What does this relate to?
a. All these materials when welded will be free from
solidification issues/cracking
b. All these materials will have a guaranteed
minimum UTS value of 500N/mm2, this will help
prevent the formation of hydrogen cracking
c. All these materials will have a probable freedom
from lamellar tearing when welded
d. All these materials have properties of zero
ductility
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Question 9
Question 6
One of your welding inspectors informs you that
during welding one of the welders is using an
excessive long arc length. Which of the following
issues could be caused by this situation?
a. An increase in hydrogen content in the weld
b. An increased risk of carbide precipitation
occurring
c. An increased risk of solidification cracking
occurring
d. An increased risk of lamellar tearing occurring
after welding.
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Question 8
Which of the following could be used to prevent
the formation of hydrogen cracking?
a. The use of E8018 electrodes in standard
packaging
b. The use of E8010 electrodes, baked to 350°C
prior to use to remove moisture
c. The use of E6012 electrodes, used in a dried
condition will give a lower UTS value which
will give an increased elongation value
d. All options are incorrect
Copyright © TWI Ltd
Question 10
One of your inspectors suggests increasing the
restraint on all single V butt joints to reduce
distortion. Which of the following may have
detrimental affect of this?
During the inspection of the materials prior to fabrication
one of the NDT inspection personnel reports back to you
that he has detected lamellar type defects running in the
center of the parent plate, sub-surface. Which of the
following is correct?
a. An increase risk of solidification cracking and
lamellar tearing
b. An increased risk of solidification and
hydrogen cracking
c. An increased risk of weld decay and hydrogen
cracking
d. All options are correct
a. The defects detected would most likely be plate
laminations and definitely not lamellar tearing
b. Lamellar tearing does not happen sub surface, it is a
surface breaking cracking mechanism
c. If its been located in the center of the plate then it
would most likely be solidification cracking
d. NDT does not locate lamellar tearing it requires
through thickness ductility testing to locate it when
present
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Copyright © TWI Ltd
11‐12
Se ct ion 1 2
W e ld Fr a ct u r e s
12
W e ld Fr a ct ur es
Welds m ay suffer t hree different fract ure m echanism s:



Duct ile.
Brit t le.
Fat igue.
Oft en a com plet e fract ure of a weldm ent will be a com binat ion of fract ure t ypes
eg init ially fat igue followed by final duct ile fract ure.
1 2 .1
D uct ile fr a ct ur e s
Occur in inst ances wher e t he st rengt h and t he cross- sect ional area of t he
m at erial are insufficient t o carr y t he applied load.
Such fract ures ar e com m only seen on m at erial and welding procedur e t ensile
t est specim ens wher e failure is accom panied by yielding, st ret ching and
t hinning as shown below.
The fract ure edges ar e at 45° t o t he applied load a nd ar e known as shear lips.
1 2 .2
Br it t le fr a ct u r e
I s a fast , unst able t ype of fract ure which can lead t o cat ast r ophic failure.
The phenom enon was first ident ified during World War 2 when m any Libert y
Ships broke in t wo for no appar ent r eason. Since t hat t im e m any brit t le failures
have occur red in bridges, boilers, pr essure v essels et c som et im es wit h loss of
life and always wit h expensive dam age.
The risk of brit t le fract ure increases;





WI S10- 30816
Weld Fract ures
As t he t em perat ur e ( am bient or oper at ional) decr eases.
Wit h t he t ype and increasing t hickness of t he m at erial.
Wher e high levels of residual st resses ar e pr esent .
I n t he pr esence of not ches.
I ncreased st rain rat e ie speed of loading.
12-1
Copyright © TWI Lt d
Court esy of Douglas E. William s, P.E., Welding Handbook, Vol.1, Nint h Edit ion, reprint ed by
perm ission of t he Am erican Welding Society.
Effect of not ch on a t ensile specim en.
Dist inguishing feat ures of a brit t le fract ur e ar e:




Surface is flat and at 90° t o t he applied load.
Will show lit t le or no plast ic deform at ion.
The surface will be r ough and m ay be cryst alline in appearance.
May show chev rons which will point back t o t he init iat ion sour ce.
Brit t le fract ure surface on a CTOD t est piece.
WI S10- 30816
Weld Fract ures
12-2
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1 2 .3
Fa t igue fr a ct u r e
Fat igue fract ur es occur in sit uat ions wher e loading is of a cyclic nat ure and at
st ress levels w ell below t he yield st ress of t he m at erial.
Typically fat igue cracks will be found on bridges, cranes, aircraft and it em s
affect ed by out of balance or vibrat ing forces.
I nit iat ion t akes place from st r ess concent rat ions such as changes of sect ion,
arc- st rikes, t oes of welds. Ev en t he best designed and m ade welds have som e
degr ee of st ress concent rat ion.
As fat igue crack s t ak e t im e first ly t o init iat e t hen t o gr ow, t his slow progression
allows such crack s t o be found by regular inspect ion schedules on t hose it em s
known t o be fat igue sensit ive.
The gr owt h r at e of fat igue cr ack s is dependant on t he loading and t he num ber
of cycles. I t is not t im e dependant
Fat igue failures are not rest rict ed t o any one t ype of m at erial or t em perat ur e
range. St r ess- relief has lit t le effect upon fat igue life.
St ruct ures known t o be at risk of fat igue failure ar e usually designed t o codes
t hat acknowledge t he risk and lays down t he rules and calculat ions t o predict it s
design life.
Typical fat igue fract ure in a T j oint .
WI S10- 30816
Weld Fract ures
12-3
Copyright © TWI Lt d
I dent ifying feat ures of fat igue fract ure ar e:





Ver y sm oot h fract ur e surface, alt hough m ay have st eps due t o m ult iple
init iat ion point s.
Bounded by cur ved crack fr ont .
Bands m ay be visible indicat ing crack progression.
I nit iat ion point opposit e curv e crack fr ont .
Surface at 90° t o applied loading.
Fat igue crack s som et im es st op of t heir own accord if t he crack runs int o an area
of low st r ess. On t he ot her hand t hey m ay grow unt il t he rem aining crosssect ion is insufficient t o support t he applied loads. At t his point final failure will
t ake place by a secondary m echanism ie duct ile or brit t le.
WI S10- 30816
Weld Fract ures
12-4
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Fracture Mechanisms
 Ductile fracture.
 Brittle fracture.
 Fatigue fracture.
Weld Fractures
Section 12
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Copyright © TWI Ltd
Fracture Mechanisms
Ductile Fracture
Ductile (overload) fracture appears when
yielding and deformation precedes failure
Ductile Fracture
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Copyright © TWI Ltd
Ductile Fracture
Ductile fracture distinguish features
 It is the result of overloading
 Evidence of gross yielding or plastic
deformation
 The fracture surface is rough and torn
 The surface shows 45° shear lips or have
surfaces inclined at 45° to the load direction
(because maximum shear plane is at 45° to
the load!)
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Fracture Mechanisms
Brittle Fracture
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12‐1
Brittle Fracture
Brittle fracture
It is a fast, unstable type of fracture.
Brittle Fracture
Brittle fracture
It is a fast, unstable type of fracture.
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Brittle Fracture
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Brittle Fracture
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Brittle Fracture
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Brittle Fracture
Brittle fracture distinguish features
 There is little or no plastic deformation before
failure
 The crack surface may show chevron marks
pointing back to the initiation point
 In case of impact fracture, the surface is
rough but not torn and will usually have a
crystalline appearance
 The surface is normally perpendicular to the
load
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12‐2
Brittle Fracture
Factors affecting brittle fracture
 Temperature (transition curve, convergence of
YS and UTS as the temperature is reduced)
 Crystalline structure (b.c.c. vs. f.c.c.)
 Material toughness
 Residual stress
 Strain rate (YS increase but UTS remain
constant)
 Material thickness (restrain due to surrounding
material)
 Stress concentrations/weld defects
Brittle Fracture
Causes for brittle fracture
 Presence of weld defects (poor quality)
 Poor toughness in parent material (wrong
choice)
 Poor toughness in HAZ (to high heat input)
 High level of residual stress (no PWHT, wrong
design)
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Fracture Mechanisms
Fatigue Fracture
Fatigue fracture distinguish features
 Crack growth is slow.
 It initiate from stress concentration points.
 Load is considerably below the design or yield stress level.
 The surface is smooth.
 The surface is bounded by a curve.
 Bands may sometimes be seen on the smooth surface 'beach marks'. They show the progress of the crack front
from the point of origin.
 The surface is 90° to the load.
 Final fracture will usually take the form of gross yielding
(as the maximum stress in the remaining ligament
increase!).
 Fatigue crack need initiation + propagation periods.
Fatigue Fracture
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Fatigue Fracture
If a material is subjected to a static load, final
rupture is preceded by very large strains.
Fatigue Fracture
Location: Any stress concentration area.
Steel Type: All steel types.
If the same material is subjected to cyclic
loads, failure may occur:
 At stress well below elastic limit.
 With little or no plastic deformation.
Susceptible Microstructure: All grain
structures.
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12‐3
Fatigue Fracture
 Fatigue cracks occur under cyclic stress
conditions.
 Fracture normally occurs at a change in
section, notch and weld defects ie stress
concentration area.
 All materials are susceptible to fatigue
cracking.
 Fatigue cracking starts at a specific point
referred to as a initiation point.
 The fracture surface is smooth in appearance
sometimes displaying beach markings.
 The final mode of failure may be brittle or
ductile or a combination of both.
Fatigue Fracture
Precautions against Fatigue Cracks
 Toe grinding, profile grinding.
 The elimination of poor profiles.
 The elimination of partial penetration welds
and weld defects.
 Operating conditions under the materials
endurance limits.
 The elimination of notch effects eg mechanical
damage cap/root undercut.
 The selection of the correct material for the
service conditions of the component.
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Fatigue Fracture
Fatigue Fracture
Points of initiation
Smooth fracture surface
Fatigue cracking at the weld toe
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Fatigue Fracture
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Products Liable to Fatigue Failure
Pressure vessels
Aerospace
Piping systems
Oil/gas platforms
Ductile fracture
Beach Marks
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12‐4
Products Liable to Fatigue Failure
Overhead Cranes
Fatigue Fracture
Lifting equipment
Fatigue fracture occurs in structures subject to
repeated application of tensile stress.
Crack growth is slow (in same cases, crack may grow
into an area of low stress and stop without failure).
Engineering plant
Rotating equipment
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Fractures
A large C-Mn structure is due for inspection after
prolonged use.
It has been used in a variety of environments
including temperatures below zero and at times
subjected to intense cyclic loading.
There are a number of failed joints within the
structure which you have to assess and report
on.
Question 1
A failure has occurred at the termination of a
fillet weld. Part of the surface condition of the
fractured surface shows variations in colour
contrast between different parts. This can be
described as:
a.
b.
c.
d.
Beach marks
Shear lips
Reduction in area
Crystallization marks
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Question 2
You discover a thick section failure, with a flat
surface, over one metre long. You need to
establish the initiation point of this failure. What
feature on the failed surface could help you to
find this?
a.
b.
c.
d.
Crystalline zone
Chevron marks
Crescent marks
Crack direction line
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Question 3
Cyclic loading can cause failure over time. What
best describes this?
a.
b.
c.
d.
Repeated loading of varying magnitude
Loads above the UTS of the material
Stress above the Rm point
Impact loading at low temperatures
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12‐5
Question 4
Brittle failure is consistent with which
combinations?
Question 5
On the failed structure, some of the failures
show distinct initiation points. Which of the
following is more likely to be these points?
a. High temperature and static loading
b. Low temperature and residual stress
c. Temperatures that vary considerably and a
load below Re
d. Temperatures above ambient and low loading
a.
b.
c.
d.
Concave weld features
Mitre like weld features
Convex weld features
Unequal leg length features
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Question 6
Question 7
Brittle fracture occurs at:
Which failure combination is most common?
a.
b.
c.
d.
a.
b.
c.
d.
The speed of light
Crack propagation is very slow
The speed of sound
Crack propagation is measured at 10mm per
minute
Fatigue to brittle
Ductile to Brittle
Ductile to Fatigue
Fatigue to Ductile
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Question 8
Which of the following materials does not suffer
from fatigue failure?
a.
b.
c.
d.
HSLA
316L stainless steel
Q/T steels
None of the options are correct
Question 9
One of the failed joints on the structure, has a
torn feature with shear lips at the point of
failure. What is the most likely cause of this
failure?
a.
b.
c.
d.
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Cyclic loading
High residual stress
Over loading
Over loading in combination with low
temperatures
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12‐6
Question 10
Some of the failures show a smooth flat surface.
This is consistent with?
a.
b.
c.
d.
Sudden failure
Slow, progressive crack propagation
Loading above the UTS value
Ductile failure
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12‐7
Se ct ion 1 3
W e ldin g Sym bols
13
W e ldin g Sym bols
A weld j oint can be r epresent ed on an engineering drawing by m eans of a
det ailed sket ch showing ev er y det ail and dim ension of t he j oint preparat ion - as
shown below.
8- 12°
≈R6
1- 3m m
1- 4m m
Single U pr e pa r a t ion.
While t his m et hod of represent at ion gives com prehensive inform at ion, it can be
t im e- consum ing and can also ov erburden t he drawing.
An alt ernat ive m et hod is t o use a sym bolic repr esent at ion t o specify t he
required inform at ion - as shown below for t he sam e j oint det ail.
Sym bolic r e pr e se nt a t ion h a s follow ing a dv a nt a ge s:



Sim ple and quick t o put on t he drawing.
Does not over- burden t he drawing.
No need for an addit ional view - all welding sym bols can be put on t he m ain
assem bly drawing.
Sym bolic r e pr e se nt a t ion h a s follow ing disa dva nt a ge s:



Can only be used for st andard j oint s ( eg BS EN I SO 9692) .
Ther e is not a way of giving precise dim ensions for j oint det ails.
Som e t raining is necessary in order t o int erpret t he sym bols cor rect ly.
WI S10- 30816
Welding Sym bols
13-1
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1 3 .1
St a nda r ds for sym bolic r e pr e se nt a t ion of w e lde d j oint s on dr a w in gs
Ther e ar e t wo principal st andards t hat are used for w elding sym bols:
Eu r ope a n St a n da r d
BS
EN
I SO 2553
–
Welded,
brazed
and
soldered
j oint s
–
Sy m bolic
represent at ion on dr awings.
Am e r ica n St a nda r d
AWS A2.4 – St andard Sym bols for Welding, Brazing, and Non- dest ruct ive
Exam inat ion.
These st andards ar e v er y sim ilar in m any respect s, but t her e are also som e
m aj or differences t hat need t o be underst ood t o avoid m is- int erpret at ion.
Det ails of t he Eur opean St andard are given in t he following sub- sect ions wit h
only brief inform at ion about how t he Am er ican St andard differs from t he
Eur opean St andard.
Ele m e nt a r y W e ldin g Sym bols
Various t ypes of weld j oint are represent ed by a sym bol t hat is int ended t o help
int erpr et at ion by being sim ilar t o t he shape of t he w eld t o be m ade.
Exam ples of sym bols used by BS EN I SO 2553 are shown on following pages.
WI S10- 30816
Welding Sym bols
13-2
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13.2
Elementary welding symbols
Designation
Square butt weld
Illustration of joint preparation
Symbol
Single V butt weld
Single bevel butt weld
Single V butt weld with
broad root face
Single bevel butt weld with
broad root face
Single U butt weld
Single J butt weld
Fillet weld
Surfacing (cladding)
Backing run
(back or backing weld)
Backing bar
WIS10-30816
Welding Symbols
13-3
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1 3 .3
Com bin a t ion of e le m e nt a r y sym bols
For sym m et rical welds m ade fr om bot h sides, t he applicable elem ent ary
sym bols are com bined – as shown below.
D e sign a t ion
I llust r a t ion of j oint pr e pa r a t ion
Sym bol
Double V but t
weld ( X weld)
Double bev el but t weld
( K weld)
Double U but t weld
Double J but t weld
WI S10- 30816
Welding Sym bols
13-4
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1 3 .4
Supp le m e nt a r y sy m b ols
Weld sym bols m ay be com plem ent ed by a sym bol t o indicat e t he required
shape of t he w eld.
Ex a m ple s of supple m e n t a r y sym bols a nd h ow t he y a r e a pplie d a r e given be low .
D e sign a t ion
I llust r a t ion of j oint p r e p a r a t ion
Sym bol
Flat ( flush) single V
but t weld
Convex double V
but t weld
Concav e fillet weld
Flat ( flush) single V
but t weld wit h flat
( flush) backing run
Single V but t weld
wit h broad root
face and backing
run
Fillet weld wit h
bot h t oes blended
sm oot hly
N ot e : I f t he weld sy m bol does not hav e a supplem ent ary sym bol t hen t he
shape of t he w eld surface does not need t o be indicat ed precisely.
WI S10- 30816
Welding Sym bols
13-5
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1 3 .5
Posit ion of sy m bols on dr a w ings
I n order t o be able t o pr ovide com prehensive det ails for w eld j oint s, it is
necessary t o dist inguish t he t wo sides of t he w eld j oint .
The way t his is done, according t o BS EN I SO 2553, is by m eans of:


An arr ow line.
A dual refer ence line consist ing of a cont inuous line and a dashed line.
Below illust rat es t he m et hod of r epr esent at ion.
3
2a
1 =
Arrow line
2a = Reference line
( cont inuous line)
2b = I dent ificat ion line
( dashed line)
3 =
Welding sym bol
( single V j oint )
1
2b
Joint line
1 3 .6
Re la t ionship be t w e e n t he a r r ow line a nd t h e j oint lin e
One end of t he j oint line is called t he a r r ow side and t he opposit e end is called
ot he r side .
The ar row side is always t he end of t he j oint line t hat t he arrow line point s t o
( and t ouches) .
I t can be at eit her end of t he j oint line and it is t he draught sm an who decides
which end t o m ak e t he arr ow side.
Below illust rat es t hese principles.
‘arrow side’
arrow line
‘other side’
‘other side’
‘arrow side’
‘other side’
‘arrow side’
arrow line
WI S10- 30816
Welding Sym bols
‘arrow side’
arrow line
‘other side’
arrow line
13-6
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Ther e ar e som e conv ent ions about t he ar r ow line:



I t m ust t ouch one end of t he j oint line.
I t j oins one end of t he cont inuous refer ence line.
I n case of a non- sym m e t r ica l j oint , such as a single bevel j oint , t he arr ow
line m ust point t owards t he j oint m em ber t hat will have t he weld
preparat ion put on t o it ( as shown below) .
An exam ple of how a single- bevel but t j oint should be repr esent ed is shown
below.
1 3 .7
Posit ion of t he r e fe r e nce line a n d posit ion of t h e w e ld sym bol
The r efer ence line should, wherev er possible, be drawn parallel t o t he bot t om
edge of t he drawing ( or perpendicular t o it ) .
For a non- sym m et rical weld it is essent ial t hat t he arr ow side and ot her side of
t he weld be dist inguished.
The conv ent ion for doing t his is:


Sym bols for t he weld det ails required on t he arr ow side m ust be placed on
t he cont inuous line.
Sym bols for t he weld det ails on ot her side m ust be placed on t he dashed
line.
WI S10- 30816
Welding Sym bols
13-7
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1 3 .8
Posit ion s of t h e cont inuou s line a n d t he da she d lin e
BS EN ISO 2553 allows t he dashed line t o be eit her above or below t he cont inuous line
– as shown below.
or
I f t he weld is a sym m et rical weld t hen it is not necessary t o dist inguish bet ween
t he t wo sides and BS EN I SO 2553 st at es t hat t he dashed line should be
om it t ed. Thus, a single V but t weld wit h a backing run can be shown by eit her
of t he four sym bolic represent at ions shown below.
Single V weld wit h a backing run
Arr ow side
Ot her side
Arr ow side
Ot her side
Ot her side
Arr ow side
Ot her side
Arr ow side
N ot e : This flexibilit y wit h t he posit ion of t he cont inuous and dashed lines is an
int erim m easur e t hat BS EN I SO 2553 allows so t hat old drawings ( t o t he
obsolet e BS 499 Part 2, for exam ple) can be conv enient ly conv ert ed t o show
t he EN m et hod of represent at ion.
1 3 .9
D im e nsion ing of w e ld s
Ge n e r a l r ule s
Dim ensions m ay need t o be specified for som e t ypes of w eld and BS EN I SO
2553 specifies a convent ion for t his.



Dim ensions for t he cross- sect ion of t he w eld are w rit t en on t he left - hand
side of t he sym bol.
Lengt h dim ensions for t he weld are writ t en on t he right hand side of t he
sym bol.
I n t he absence of any indicat ion t o t he cont rar y, all but t welds ar e full
penet rat ion w elds.
WI S10- 30816
Welding Sym bols
13-8
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1 3 .9 .1
Sym bols for cr oss- se ct ion dim e n sions
The following let t ers ar e used t o indicat e dim ensions:
a
Z
s
Fillet weld t hroat t hickness.
Fillet weld leg lengt h.
Penet rat ion dept h.
( Applicable t o part ial penet rat ion
fillet s..)
but t
welds and
deep
penet r at ion
Som e exam ples of how t hese sym bols ar e used are shown below.
10m m
Part ial penet rat ion
single V but t weld
s1 0
Z8
Fillet weld wit h
8m m leg
8m m
a6
Fillet weld wit h
6m m t hroat
6m m
WI S10- 30816
Welding Sym bols
13-9
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1 3 .9 .2
Sym bols for le ngt h dim e nsion s
To specify weld lengt h dim ensions and, for int erm it t ent welds t he num ber of
individual weld lengt hs ( weld elem ent s) , t he following let t ers ar e used:
l
( e)
n
Lengt h of w eld.
Dist ance bet w een adj acent weld elem ent s.
Num ber of w eld elem ent s.
The use of t hese let t ers is illust rat ed for t he int erm it t ent double- sided fillet weld
shown below.
100m m
8
150m m
Plan view
End view
zZ
n x l ( e)
Z
n x l ( e)
Z8
Z8
3 × 150 ( 100)
3 × 150 ( 100)
N ot e : dashed line not r equired because it is a sym m et rical weld.
WI S10- 30816
Welding Sym bols
13-10
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I f an int erm it t ent double- sided fillet weld is t o be st agger ed, t he conv ent ion for
indicat ing t his is shown below.
l
( e)
z
Plan view
1 3 .9 .3
End view
Com ple m e nt a r y in dica t ions
Com plem ent ary indicat ions m ay be needed t o specify ot her charact erist ics of
welds.
Exam ples ar e:

Field or sit e w elds is indicat ed by a flag.

A peripheral weld, t o be m ade all around a part , is indicat ed by a circle.
WI S10- 30816
Welding Sym bols
13-11
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1 3 .1 0
I ndica t ion of t he w e lding pr oce ss
I f r equired, t he w elding process is t o be sy m bolised by a num ber writ t en
bet ween t he t wo branches of a fork at t he end of t he reference line – as shown
below.
Som e welding process
designat ions
111
1 3 .1 1
111
121
131
135
141
=
=
=
=
=
MMA
SAW
MI G
MAG
TI G
Ot h e r I n for m a t ion in t h e t a il of t h e r e f e r e n ce lin e
I n addit ion t o specifying t he w elding process, ot her infor m at ion can be added t o
an ope n t a il ( shown abov e) such as t he NDT accept ance lev el t he w or king
posit ion and t he filler m et al t ype and BS EN I SO 2553 defines t he sequence t hat
m ust be used for t his infor m at ion.
A closed t ail can also be used int o which refer ence t o a specific inst ruct ion can
be added – as shown below.
WPS 014
1 3 .1 2
W e ld sym bols in a ccor da nce w it h AW S 2 .4
Many of t he sym bols and convent ions t hat are specified by BS EN I SO 2553 are
t he sam e as t hose used by AWS.
The m aj or differ ences are:



Only one reference line is used ( a cont inuous line) .
Sym bols for w eld det ails on t he a r r ow side go u nde r n e a t h t h e r e fe r e n ce
lin e .
Sym bols for w eld det ails on t he ot he r side go on t op of t h e r e f e r e n ce
lin e .
WI S10- 30816
Welding Sym bols
13-12
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These differences ar e illust rat ed by t he following exam ple.
Arrow side
Ot her side
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Welding Sym bols
13-13
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Weld Symbols on Drawings
Joints in drawings may be indicated
 By detailed sketches, showing every dimension.
Welding Symbols
 By symbolic representation.
Section 13
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Weld Symbols on Drawings
A method of transferring information from the design
office to the workshop is:
Please weld
here
The above information does not tell us much about the
wishes of the designer. We obviously need some sort
of code which would be understood by everyone.
Most countries have their own standards for symbols.
Some of them are AWS A2.4 & BS EN ISO 2553
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Weld Symbols on Drawings
Advantages of symbolic representation
 Simple and quick plotting on the drawing.
 Does not over-burden the drawing.
 No need for additional view.
 Gives all necessary indications regarding the
specific joint to be obtained.
Disadvantages of symbolic representation
 Used only for usual joints.
 Requires training for properly understanding of
symbols.
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Weld Symbols on Drawings
Arrow Line
(BS EN ISO 2553 & AWS A2.4)
Convention of the arrow line
The symbolic representation includes
 An arrow line.
 A reference line.
 An elementary symbol.
The elementary symbol may be completed by
 A supplementary symbol.
 A means of showing dimensions.
 Some complementary indications.
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 Shall touch the joint intersection.
 Shall not be parallel to the drawing.
 Shall point towards a single plate preparation
(when only one plate has preparation).
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13‐1
Reference Line
(AWS A2.4)
Convention of the reference line
 Shall touch the arrow line.
 Shall be parallel to the bottom of the drawing.
Reference Line
(BS EN ISO 2553)
Convention of the reference line
 Shall touch the arrow line.
 Shall be parallel to the bottom of the drawing.
 There shall be a further broken identification
line above or beneath the reference line (Not
necessary where the weld is symmetrical and
should be omitted).
or
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Elementary Welding Symbols
(BS EN ISO 2553 & AWS A2.4)
Convention of the elementary symbols
 Various categories of joints are characterised by an
elementary symbol.
 The vertical line in the symbols for a fillet weld,
single/double bevel butts and a J-butt welds must
always be on the left side.
Weld type
Square edge
butt weld
Sketch
Symbol
Single-v
butt weld
Elementary Welding Symbols
Weld type
Sketch
Symbol
Single-V butt
weld with
broad root face
Single bevel
butt weld
Single bevel
butt weld with
broad root face
Backing run
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Elementary Welding Symbols
Weld type
Sketch
Symbol
Single-U
butt weld
Double Side Weld Symbols
(BS EN ISO 2553 & AWS A2.4)
Convention of the double side weld symbols
Representation of welds done from both sides
of the joint intersection, touched by the arrow
head.
Single-J
butt weld
Surfacing
Fillet weld
Double bevel
Double J
Fillet weld
Double V
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Double U
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13‐2
Dimensions
Convention of dimensions
In most standards the cross sectional dimensions are
given to the left side of the symbol, and all linear
dimensions are give on the right side.
BS EN ISO 2553
a = Design throat thickness.
s = Depth of Penetration, Throat thickness.
z = Leg length (min material thickness).
Supplementary Symbols
(BS EN ISO 2553 & AWS A2.4)
Convention of supplementary symbols
Supplementary information such as welding
process, weld profile, NDT and any special instructions
Ground flush
AWS A2.4
 In a fillet weld, the size of the weld is the leg length.
 In a butt weld, the size of the weld is based on the
depth of the joint preparation.
111
MR
M
Removable
backing strip
Permanent
backing strip
Welding process
numerical BS EN
Further supplementary information, such as WPS number, or
NDT may be placed in the fish tail
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Supplementary Symbols
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Welding Symbols
(BS EN ISO 2553 & AWS A2.4)
Convention of supplementary symbols
Supplementary information such as welding process,
weld profile, NDT and any special instructions
Toes to be ground smoothly
(BS EN only)
Site Weld
BS EN ISO 2553
Concave or Convex
Weld all round
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BS EN ISO 2553
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BS EN ISO 2553
Reference lines
Arrow line
Other side
Arrow side
Arrow side
Arrow side
Other side
Arrow side
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13‐3
BS EN ISO 2553
BS EN ISO 2553
Other side
Both sides
Other side
Both sides
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BS EN ISO 2553
a
BS EN ISO 2553
b
Mitre
c
Convex
Toes shall
be blended
Concave
d
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BS EN ISO 2553
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BS EN ISO 2553
Peripheral welds
Field weld (site weld)
NDT
The component requires
NDT inspection
Welding to be carried
out all round component
(peripheral weld)
WPS
Additional information,
the reference document
is included in the box
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z10
10
10
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13‐4
BS EN ISO 2553
a = Design throat thickness
s = Depth of penetration, throat thickness
z = Leg length (min material thickness)
a = (0.7 x z)
BS EN ISO 2553
n = number of weld elements
l = length of each weld element
(e) = distance between each weld element
n x l
a4
z
a
(e)
4mm Design throat
Welds to be
staggered
s
z6
s6
2 x 40 (50)
3 x 40 (50)
6mm Actual throat
6mm leg
111
Process
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BS EN ISO 2553
BS EN ISO 2553
All dimensions in mm
5
80
80
All dimensions in mm
z5
3 x 80 (90)
z6
3 x 80 (90)
6
80
5
80
90
90
3 x 80 (90)
z6
3 x 80 (90)
80
6
8
6
80
z8
90
90
90
90
8
6
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BS EN ISO 2553
BS EN ISO 2553
MR
M
Single V butt with
permanent backing strip
Single V butt flush cap
Single U butt with
removable backing strip
Single bevel butt
Double bevel butt
Single U butt with sealing run
Single bevel butt
Single J butt
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13‐5
BS EN ISO 2553
s10
10
BS EN ISO 2553
Square butt weld
Plug weld
15
Partial penetration single V butt
‘S’ indicates the depth of penetration
Resistance spot weld
Steep flanked
single V butt
Resistance seam weld
Surfacing
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BS EN ISO 2553
Compound Weld Ex
BS EN ISO 2553
Numerical values for welding processes
111: MMA welding with covered electrode
121: Sub-arc welding with wire electrode
131: MIG welding with inert gas shield
135: MAG welding with non-inert gas shield
136: Flux core arc welding
141: TIG welding
311: Oxy-acetylene welding
72: Electro-slag welding
15: Plasma arc welding
Complete the symbol drawing for the welded
cruciform joint provided below
All welds are welded with the MAG process and fillet welds
with the MMA process
7
35
15
10
20
30
All fillet weld leg lengths 10 mm
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BS EN ISO 2553
Compound Weld Ex
Complete the symbol drawing for the welded cruciform joint
provided below. All welds are welded with the MAG process
and fillet welds with the MMA process. z10
S30
7
35
15
135/111
10
135/111
S20
z10
20
30
z10 a 7
S35
S15
z10
All fillet weld leg lengths 10 mm
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BS EN ISO 2553
Rules
Welds this side of joint, go on the unbroken
reference line while welds the other side of the
joint, go on the broken reference line.
Symbols with a vertical line component must
be drawn with the vertical line to the left side of
the symbol.
All CSA dimensions are shown to the left of the
symbol.
All linear dimensions are shown on the right of
the symbol ie number of welds, length of welds,
length of any spaces.
Included angle and root opening are shown on
top of the symbol.
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13‐6
BS EN ISO 2553
Rules - Example
Welding Symbols
All leg lengths shall be preceded by z and throat
by a or s (in case of deep penetration welds)
z 10
3 x 50 (50)
AWS A2.4
50
50
10
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AWS Welding Symbols
Depth of
bevel
AWS Welding Symbols
Welding process
Root opening
1 (1-1/8)
1(1-1/8)
1/8
60°
Effective throat
Groove angle
GSFCAW
1/8
60°
GMAW
GTAW
SAW
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AWS Welding Symbols
AWS Welding Symbols
Welds to be staggered
3 – 10
3 – 10
3rd Operation
Sequence of
operations
SMAW
2nd Operation
Process
3
3
1st Operation
1(1-1/8)
FCAW
1/8
60°
10
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13‐7
AWS Welding Symbols
Welds on arrow side of joint go underneath
the reference line while welds the other side of
the joint, go on top of the reference line.
Symbols with a vertical line component must
be drawn with the vertical line to the left side of
the symbol.
All CSA dimensions are shown to the left of the
symbol.
All linear dimensions are shown on the right of
the symbol ie number of welds, length of welds,
length of any spaces.
Included angle and root opening are shown on
top of the symbol.
RT
Sequence of
operations
MT
MT
1(1-1/8)
AWS A 2.4 Rules
FCAW
1/8
60°
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AWS A 2.4 Rules - Example
10
3 x 50 (70)
Any Questions
?
70
50
10
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Question 1
10 Questions relating to Welding
Symbols – refer to Vessel
Drawing 1 in Appendix 3
Based on the information given, what would be
the appropriate weld symbol to BS EN ISO 2553
for the joint numbered 1, if the excess weld
metal was removed to allow ultrasonic testing
from the outside of the vessel? The joint has
been welded using the FCAW process.
136
135
a
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b
131
c
136
d
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13‐8
Question 2
Based on the information given, what would be
the appropriate weld symbol to BS EN ISO 2553
for the joint numbered 2, if it was welded from
the outside of the vessel by the SAW process
with a sealing run on the inside of the vessel?
111
15
a
b
121
c
Question 3
At position 3, what would be the appropriate
weld symbol to BS EN ISO 2553 , if a set on
nozzle type configuration, welded from the
outside of the vessel using the MMA welding
process?
a
d
111
111
131
SUB
ARC
111
b
c
d
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Question 4
At position 3, what would be the appropriate
weld symbol to BS EN ISO 2553 , if a set
through joint configuration was used and a
14mm design throat was required on the inside,
and a 20mm leg length fillet on the outside of
the vessel, using the MAG welding process?
a14
135
z20
z20
131
a14
a
135
z20
b
At position 4 on the vessel, what would be the
appropriate symbol to BS EN ISO 2553 , if a fillet
weld was required with a 26mm leg length fillet
on the outside of the flange and a 14mm design
throat on the inside on the flange?
z20
z20
135
z20
c
Question 5
a14
z26
a14
z26
z26
a14
z26
a14
c
d
a
d
b
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Question 6
At position 3 on the vessel, what would be the
appropriate weld symbol to BS EN ISO 2553 , if
a compound weld was required on the outside of
the vessel with a 30mm leg length and a 14mm
design throat weld on the inside of the vessel
using the MMA process?
a30
a14
a14
141
a14
z30
a
b
131
c
d
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2
a
MR
MR
135
111
z14
z30
At position 1, the material thickness has been
changed to 5mm. What would be the appropriate
welding symbol to BS EN ISO 2553 , if a single
sided weld from the outside of the vessel was
used with removable backing using the MAG
process?
MR
111
111
z30
Question 7
b
M
137
136
c
d
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13‐9
Question 8
Question 9
When using BS EN ISO 2553 , the term
symmetrical means?
a.
b.
c.
d.
At position 2 on the vessel, if a single sided
bevel joint was required on the dished end when
welding from the outside, in accordance with
BS EN ISO 2553 which would be the correct
symbol?
The same, arrow and other side
Different arrow and other side
Only refers to the arrow side
Only refers to the other side
a
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)
b
c
d
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Question 10
The letter s preceding a symbol dimension to
BS EN ISO 2553 means?
a.
b.
c.
d.
Weld requires flushing
Toes require blending
Depth of penetration
Standard shape
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13‐10
Se ct ion 1 4
NDT
14
NDT
Radiographic, ult rasonic, dye- penet rant and m agnet ic part icle m et hods are
briefly described below. The relat ive advant ages and lim it at ions of t he m et hods
are discussed in t erm s of t heir applicabilit y t o t he exam inat ion of w elds.
1 4 .1
Ra d iog r a p hic m e t hod s
I n all cases radiographic m et hods as applied t o welds involve passing a beam of
penet rat ing radiat ion t hrough t he t est obj ect . The t ransm it t ed radiat ion is
collect ed by som e form of sensor, which is capable of m easuring t he relat ive
int ensit ies of penet rat ing radiat ions im pinging upon it .
I n m ost cases t his sensor will be a radiographic film ; howev er t he use of
various elect r onic devices is on t he increase. These devices facilit at e so- called
real t im e radiography and exam ples m ay be seen in t he securit y check ar ea at
m ost airport s.
Digit al t echnology has enabled t he st oring of radiographs using com put er s. The
present discussion is confined t o film radiography since t his is st ill by far t he
m ost com m on m et hod applied t o welds.
1 4 .1 .1
Sour ce s of pe n e t r a t in g r a dia t ion
Penet rat ing radiat ions m ay be generat ed fr om high- energy elect r on beam s, in
which case t hey are t erm ed X ray s, or fr om nuclear disint egrat ions ( at om ic
fission) , in which case t hey are t erm ed γ- rays. Ot her form s of penet rat ing
radiat ion exist but t hey are of lim it ed int erest in weld radiography.
1 4 .1 .2
X rays
X rays used in t he indust rial radiography of welds generally have phot on
energies in t he range 30keV up t o 20MeV. Up t o 400keV t hey are generat ed by
conv ent ional X ray t ubes which dependant upon out put m ay be suit able for
port able or fixed inst allat ions.
Port abilit y falls off rapidly wit h increasing kilovolt age and radiat ion out put .
Above 400keV X ray s are produced using devices such as bet at r ons and linear
accelerat ors. These dev ices are not generally suit able for use out side of fixed
inst allat ions. All sources of X rays produce a cont inuous spect rum of radiat ion,
reflect ing t he spread of kinet ic energies of elect rons wit hin t he elect ron beam .
Low energy radiat ions are m ore easily absorbed and t he presence of low energy
radiat ions, wit hin t he X ray beam , gives rise t o bet t er r adiographic cont rast and
t herefor e bet t er radiographic sensit ivit y t han is in t he case wit h γ- rays which
are discussed below.
Convent ional X ray unit s ar e capable of per for m ing high qualit y radiography on
st eel of up t o 60m m t hickness, bet at r ons and linear accelerat ors ar e capable of
penet rat ing in excess of 300m m of st eel.
WI S10- 30816
NDT
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1 4 .1 .3
γ- r a ys
The early sources of γ- rays used in indust rial radiography w er e in general
com posed of nat urally occurring radium . The act ivit y of t hese sources was not
very high, t herefor e t hey wer e physically rat her large by m odern st andards
ev en for quit e m odest out put s of radiat ion and t he radiographs pr oduced by
t hem wer e not of a part icularly high st andard.
Radium sources wer e also ext r em ely hazardous t o t he user due t o t he
product ion of radioact ive radon gas as a pr oduct of t he fission react ion. Since
t he advent of t he nuclear age it has been possible t o art ificially produce
isot opes of m uch higher specific act ivit y t han t hose occur ring nat urally and
which do not pr oduce hazardous fission pr oduct s. Unlike t he X- ray sources γsour ces do not pr oduce a cont inuous dist ribut ion of quant um energies. γsour ces produce a num ber of specific quant um energies which ar e unique for
any part icular isot ope.
Four isot opes ar e in com m on use for t he radiography of welds; t hey ar e in
ascending order of radiat ion energy: t hulium 90, yt t erbium 169, iridium 192
and cobalt 60. I n t erm s of st eel t hulium 90 is useful up t o a t hickness of 7m m
or so, it ’s energy is sim ilar t o t hat of 90keV X rays and due t o it ’s high specific
act ivit y useful sources can be pr oduced wit h physical dim ensions of less t han
0.5m m .
Yt t erbium 169 has only fairly recent ly becom e available as an isot ope for
indust rial use, it ’s ener gy is sim ilar t o t hat of 120keV X ray s and it is useful for
t he radiography of st eel up t o appr oxim at ely 12m m t hickness.
I ridium 192 is probably t he m ost com m only encount er ed isot opic sour ce of
radiat ion used in t he radiographic exam inat ion of w elds, it has a relat ively high
specific act ivit y and high out put sources wit h physical dim ensions of 2- 3m m are
in com m on usage, it ’s energy is approxim at ely equivalent t o t hat of 500 keV X
rays and it is useful for t he radiography of st eel in t he t hickness range 1075m m .
Cobalt 60 has an energy approxim at ing t o t hat of 1.2MeV X ray s, due t o t his
relat ively high energy suit able source cont ainer s are large and rat her heavy.
Cobalt 60 sour ces ar e for t his r eason not fully port able. They are useful for t he
radiography of st eel in t he t hickness range 40- 150m m .
The m aj or advant ages of using isot opic sources ov er X rays ar e:
a
b
c
The increased port abilit y.
The lack of t he need for a pow er sour ce.
Low er init ial equipm ent cost s.
Against t his t he qualit y of radiographs produced by γ- ray t echniques is inferior
t o t hat produced by X ray t echniques, t he hazards t o personnel m ay be
increased ( if t he equipm ent is not properly m aint ained, or if t he operat ing
per sonnel have insufficient t raining) and due t o t heir lim it ed useful lifespan new
isot opes hav e t o be pur chased on a r egular basis ( so t hat t he operat ing cost s of
a γ- ray source m ay exceed t hose of an X ray source) .
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1 4 .1 .4
Ra d iog r a p hy of w e ld s
Radiographic t echniques depend upon det ect ing differ ences in absorpt ion of t he
beam ie: changes in t he effect ive t hickness of t he t est obj ect , in order t o r ev eal
defect ive areas.
Volum et ric weld defect s such as slag inclusions ( ex cept in som e special cases
wher e t he slag absorbs radiat ion t o a great er ext ent t han does t he weld m et al)
and various form s of gas porosit y are easily det ect ed by radiographic
t echniques due t o t he large negat ive absorpt ion difference bet w een t he par ent
m et al and t he slag or gas.
Planar defect s such as cracks or lack of side w all or int er- run fusion are m uch
less likely t o be det ect ed by radiography since such defect s m ay cause lit t le or
no change in t he penet rat ed t hickness. Wher e defect s of t his t ype are likely t o
occur ot her NDE t echniques such as ult rasonic t est ing are pr eferable t o
radiography. This lack of sensit ivit y t o planar defect s m ak es radiogr aphy an
unsuit able t echnique wher e a fit ness- for- purpose appr oach is t aken when
assessing t he accept abilit y of a w eld.
How ev er, film radiography produces a perm anent record of t he w eld condit ion,
which can be archived for fut ur e reference; it also provides an excellent m eans
of assessing t he welder’s per form ance and for t hese r easons it is oft en st ill t he
preferr ed m et hod for new const ruct ion.
Figur e 1 4 .1 X r a y e quipm e nt .
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NDT
Figur e 1 4 .2 Ga m m a - r a y e quipm e n t .
14-3
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Figur e 1 4 .3 X r a y of a w e lde d se a m sh ow in g por osit y.
1 4 .1 .5
Ra diogr a phic t e st in g








1 4 .1 .6
Adv a nt a ge s
Per m anent r ecord
Good for sizing non planar
defect s/ flaws
Can be used on all m at erials
Direct im age of defect s/ flaws
Real- t im e im aging
Can be posit ion inside pipe
( product ivit y)
Ver y
good
t hickness
penet rat ion available
No
power
required
wit h
gam m a










Lim it a t ions
Healt h hazard. Safet y ( im port ant )
Classified
work er s,
m edicals
required
Sensit ive t o defect orient at ion
Not good for planar defect det ect ion
Lim it ed abilit y t o det ect fine cracks
Access t o bot h sides required
Skilled int erpr et at ion required
Relat ively slow
High capit al out lay and running
cost s
I sot opes hav e a half life ( cost )
Ult r a son ic m e t hods
The v elocit y of ult rasound in any given m at erial is a const ant for t hat m at erial
and ult rasonic beam s t rav el in st raight lines in hom ogeneous m at erials. When
ult rasonic wav es pass from a given m at erial wit h a given sound v elocit y t o a
second m at erial wit h different v elocit y refract ion and r eflect ion of t he sound
beam will occur at t he boundary bet ween t he t w o m at erials.
The sam e laws of physics apply equally t o ult rasonic wav es as t hey do t o light
waves. Because ult rasonic waves ar e r efract ed at a boundar y bet ween t w o
m at erials having different acoust ic pr opert ies, probes m ay be const ruct ed which
can beam sound int o a m at erial at ( wit hin cert ain lim it s) any given angle.
Because sound is r eflect ed at a boundary bet ween t w o m at erials having
different acoust ic pr opert ies ult rasound is a useful t ool for t he det ect ion of w eld
defect s. Because t he v elocit y is a const ant for any given m at erial and because
sound t rav els in a st raight line ( wit h t he right equipm ent ) ult rasound can also
be ut ilised t o give accur at e posit ional inform at ion about a given r eflect or.
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Careful observat ion of t he echo pat t ern of a given reflect or and it s behaviour as
t he ult rasonic probe is m ov ed t oget her wit h t he posit ional inform at ion obt ained
abov e and knowledge of t he com ponent hist or y enables t he experienced
ult rasonic operat or t o classify t he reflect or as say slag lack of fusion or a crack .
1 4 .1 .7
Equipm e nt for u lt r a sonic t e st ing
Equipm ent for m anual ult rasonic t est ing consist s of:
a

A f la w de t e ct or com pr ising:


Pulse generat or.
Adj ust able t im e base generat or wit h an adj ust able delay cont r ol.
Cat hode ray t ube wit h fully rect ified display.
Calibrat ed am plifier wit h a graduat ed gain cont rol or at t enuat or) .
b
An ult r a sonic pr obe com pr ising:




Piezo- elect ric cryst al elem ent capable of conv ert ing elect rical vibrat ions t o
m echanical vibrat ions and vice- versa.
Probe shoe, norm ally a Per spex block t o which t he cry st al is firm ly at t ached
using a suit able adhesive.
Elect rical and/ or m echanical cryst al dam ping facilit ies t o prevent excessive
ringing.
Such equipm ent is light weight and ext rem ely port able. Aut om at ed or sem iaut om at ed syst em s for ult rasonic t est ing ut ilise t he sam e basic equipm ent
alt hough in general t his will be m ult i- channel equipm ent , it is bulkier and less
port able.
Probes for aut om at ed syst em s are set in array s and som e form of m anipulat or
is necessary in order t o feed posit ional infor m at ion about t he pr obes t o t he
com put er. Aut om at ed syst em s generat e v ery large am ount s of dat a and m ake
large dem ands upon t he RAM of t he com put er . Recent advances in aut om at ed
UT have led t o a r educed am ount of dat a being recorded for a given lengt h of
weld.
Sim plified probe ar ray s have great ly reduced t he com plexit y of set t ing up t he
aut om at ed sy st em t o carr y out a part icular t ask. Aut om at ed UT syst em s now
provide a serious alt ernat ive t o radiography on such const ruct ions as pipelines
wher e a large num ber of sim ilar inspect ions allow t he unit cost of syst em
dev elopm ent t o be reduced t o a com pet it ive lev el.
Figur e 1 4 .4 Ult r a sonic e quipm e nt .
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Figur e 1 4 .5 Com pr e ssion a nd she a r w a ve pr obe s.
Figur e 1 4 .6 Sca nnin g t e chnique w it h a she a r w a ve pr obe .
Figur e 1 4 .7 Typica l scr e e n displa y w he n u sing a she a r w a ve pr obe .
1 4 .1 .8
Ult r a son ic t e st ing








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NDT
Adv a nt a ge s
Port able
( no
m ains
pow er)
bat t ery
Direct locat ion of defect ( 3
dim ensional)
Good for com plex geom et ry
Safe operat ion ( can be car ried out
next t o som eone)
I nst ant result s
High penet rat ing capabilit y
Can be done fr om one side only
Good for finding planar defect s
14-6









Lim it a t ions
No perm anent r ecord
Only fer rit ic m at erials ( m ainly)
High level of
oper at or
skill
required
Calibrat ion of equipm ent required
Special calibrat ion blocks r equired
No good for pin point ing por osit y
Crit ical
of
surface condit ions
( clean sm oot h)
Will not det ect surface defect s
Mat erial t hickness > 8m m due t o
dead zone
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1 4 .2
M a gn e t ic pa r t icle t e st ing
Surface breaking or
give rise t o leakage
leakage fields will
t hem selves and t his
ver y near surface discont inuit ies in fer r om agnet ic m at erials
fields when high levels of m agnet ic flux are applied. These
at t ract m agnet ic part icles ( finely divided m agnet it e) t o
process leads t o t he form at ion of an indicat ion.
The m agnet ic part icles m ay be visibly or fluorescent ly pigm ent ed in order t o
provide cont rast wit h t he subst rat e or conversely t he subst rat e m ay be light ly
coat ed wit h a whit e backgr ound paint in order t o cont rast wit h t he part icles.
Fluorescent m agnet ic part icles provide t he great est sensit ivit y. The part icles will
norm ally be in a liquid suspension and t his will norm ally be applied by spraying.
I n cert ain cases dr y part icles m ay be applied by a gent le j et of air. The
t echnique is applicable only t o fer rom agnet ic m at erials, which are at a
t em perat ur e below t he curie point ( about 650°C) . Th e leakage field will be
great est for linear discont inuit ies lying at right angles t o t he m agnet ic field. This
m eans t hat for a com prehensive t est t he m agnet ic field m ust nor m ally be
applied in t wo direct ions, which are m ut ually perpendicular. The t est is
econom ical t o carr y out bot h in t erm s of equipm ent cost s and rapidit y of
inspect ion. The level of operat or t r aining required is r elat ively low.
Figur e 1 4 .8 M a gne t ic pa r t icle inspe ct ion u sing a yok e .
Figur e 1 4 .9 Cr a ck fou nd using m a gne t ic pa r t icle inspe ct ion.
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1 4 .2 .1
M a gn e t ic pa r t icle t e st ing
Adv a nt a ge s
 I nexpensive equipm ent
 Direct locat ion of defect
 Not crit ical of surface condit ions
 Could be applied wit hout power
 Low skill level
 Sub defect s surface 1- 2m m
 Quick inst ant result s
 Hot t est ing ( using dry powder)
 Can be used in t he dark ( UV light
1 4 .3
Lim it a t ions
 Only m agnet ic m at erials
 May
need
to
dem agnet ise
com ponent s
 Access m ay be a pr oblem for t he
yok e
 Need power if using a yok e
 No perm anent r ecord
 Calibrat ion of equipm ent
 Test ing in t wo direct ions r equired
 Need
good light ing 500 Lux
m inim um
D ye pe n e t r a n t t e st in g
Any liquid t hat has good wet t ing propert ies will act as a penet rant . Penet rant s
are at t ract ed int o surface breaking discont inuit ies by capillary for ces. Penet rant ,
which has ent ered a t ight discont inuit y, will rem ain even when t he excess
penet rant is r em ov ed.
Applicat ion of a suit able dev eloper will encourage t he penet rant wit hin such
discont inuit ies t o bleed out . I f t her e is a suit able cont rast bet ween t he
penet rant and t he dev eloper an indicat ion visible t o t he eye will be for m ed. This
cont rast m ay be pr ovided by eit her visible or fluorescent dyes. Use of
fluorescent dy es considerably increases t he sensit ivit y of t he t echnique.
The t echnique is not applicable at ext rem es of t em perat ure. At low
t em perat ur es ( below 5°C) t he penet rant vehicle, nor m ally oil will becom e
excessively viscous and t his will cause an increase in t he penet rat ion t im e wit h
a consequent decr ease in sensit ivit y. At high t em perat ur es ( abov e 60°C) t he
penet rant will dry out and t he t echnique will not wor k.
Figur e 1 4 .1 0 M e t hods of a pplying t he r e d dye dur ing dye - pe ne t r a n t inspe ct ion.
WI S10- 30816
NDT
14-8
Copyright © TWI Lt d
Figur e 1 4 .1 1 Cr a ck fou n d usin g dye - pe ne t r a nt inspe ct ion.
1 4 .3 .1
D ye pe n e t r a n t
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Adv a nt a ge s
All m at erials ( non- porous)
Port able
Applicable t o sm all part s
wit h com plex geom et r y
Sim ple
I nexpensive
Sensit ivit y
Relat ively low skill level
( easy t o int erpr et )
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1 4 .4
Lim it a t ions
Will only det ect defect s open t o t he
surface
Requires car eful surface preparat ion
Not applicable t o porous surfaces
Tem perat ur e dependant
Cannot r et est indefinit ely
Pot ent ially hazardous chem icals
No perm anent r ecord
Tim e lapse bet ween applicat ion and
result s
Messy
Sur f a ce cr a ck de t e ct ion ( m a gne t ic pa r t icle / dye pe ne t r a nt ) : ge n e r a l
When considering t he r elat ive value of NDE t echniques, it should not be
forgot t en t hat m ost cat ast r ophic failures init iat e fr om t he surface of a
com ponent , t herefore t he value of t he m agnet ic part icle and dye Penet rant
t echniques should not be underest im at ed.
Ult rasonic inspect ion m ay not det ect near surface defect s easily since t he
indicat ions m ay be m asked by echoes arising fr om t he com ponent geom et r y
and should t herefor e be supplem ent ed by an appropriat e surface crack
det ect ion t echnique for m axim um t est confidence.
Re vie w of N D T docu m e nt a t ion
I n reviewing or car rying out an audit of NDT r eport s cert ain aspect s apply t o all
report s whilst ot hers ar e specific t o a part icular t echnique.
Ge n e r a l r e qu ir e m e nt s:
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WI S10- 30816
NDT
Dat e/ t im e/ st age of inspect ion.
Place of inspect ion.
Procedure or St andard t o which t he t est was perform ed.
St andard used for accept ance crit eria.
Mat erial t ype and t hickness.
Joint configurat ion.
All defect s ident ified, locat ed and sized.
NDT t echnicians nam e and qualificat ion.
St am ped signed and dat ed.
14-9
Copyright © TWI Lt d
Ult r a son ic spe cif ic – not e not su it a ble for a ll w e ld m e t a l t ype s

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Surface finish ie as- welded or ground.
Type of equipm ent .
Probe t ypes – com pression and shear wave.
Probe sizes – usually 10m m .
Probe fr equency – t ypically 2.5–5MHz.
Probe angles – t ypically 45, 60, 70, 90.
Type of couplant .
Calibrat ion block t ype and hole size.
Calibrat ion range set t ing.
Scanning pat t ern.
Sensit ivit y set t ing.
Recording level.
Ra diogr a phic spe cific
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Type of radiat ion – X or gam m a
Source t ype, size and st rengt h ( curies)
Tube focal spot size and pow er ( Kva)
Technique eg single wall single im age
Source/ focal spot t o film dist ance
Type and range of I QI .
Type and size of film .
Type and placem ent of int ensifying scr eens.
Exposur e t im e.
Dev elopm ent t em ps and t im es.
Recorded sensit ivit y – bet t er t han 2% .
Recorded densit y range – 2- 3.5.
M a gn e t ic p a r t icle spe cific – n ot e m e t h od su it a ble for fe r r it ic st e e ls on ly
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Met hod – wet / dry, fluor escent , cont r ast , et c.
Met hod of m agnet isat ion- DC or AC.
Equipm ent t ype – prod, yok e, perm . m agnet , bench, coils.
Prod spacing ( 7.5A/ m m ) .
Lift t est for m agnet s – 4.5kg for AC y ok e, 18kg for perm . Magnet .
Cont rast paint .
I nk t ype.
Prod/ y ok e t est scan sequence – 2 x at 45 0 t o w eld c/ l.
Light ing condit ions – 500 Lux m in for daylight , 20 Lux for UV.
UV light - 1m W/ cm 2 .
Flux m easurem ent st rips – Burm ah- Cast r ol, et c.
Pe n e t r a n t spe cific

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WI S10- 30816
NDT
Met hod – colour cont rast or fluorescent .
Surface pr eparat ion.
Penet rant t ype.
Applicat ion m et hod and t im e ( 5- 60m in) .
Met hod of r em oval.
Type and applicat ion of dev eloper.
Cont rast light – 500 Lux m in.
Black light – 20 Lux.
Operat ing t em perat ur e - 5–50 ° C.
14-10
Copyright © TWI Lt d
Non-Destructive Testing
A welding inspector should have a working
knowledge of NDT methods and their
applications, advantages and disadvantages.
Four basic NDT methods
 Magnetic particle inspection (MT).
 Dye penetrant inspection (PT).
 Radiographic inspection (RT).
 Ultrasonic inspection (UT).
NDT
Section 14
Copyright © TWI Ltd
Copyright © TWI Ltd
Radiographic Testing
The principles of radiography
 X or Gamma radiation is imposed upon a test
object.
 Radiation is transmitted to varying degrees
dependant upon the density of the material
through which it is travelling.
 Thinner areas and materials of a less density
show as darker areas on the radiograph.
 Thicker areas and materials of a greater
density show as lighter areas on a radiograph.
 Applicable to metal’s, non-metals and
composites.
Radiographic Testing
X–rays
Gamma rays
Electrically generated
Generated by the decay of
unstable atoms
Copyright © TWI Ltd
Copyright © TWI Ltd
Radiographic Testing
Radiographic Testing
Source
Source
Radiation beam
Image quality indicator
Radiation beam
Image quality indicator
Test specimen
Test specimen
Radiographic film
Radiographic film with latent image after exposure
Copyright © TWI Ltd
Copyright © TWI Ltd
14‐1
Radiographic Testing
Density - relates to the degree of darkness.
Radiographic Density
1.23
1.88
2.13
2.44
2.63
2.93
3.03
3.53 4.23
Contrast - relates to the degree of difference.
Definition - relates to the degree of sharpness.
Sensitivity - relates to the overall quality of the
radiograph.
Density strip
 Density is measured by a
densitometer.
 A densitometer should be
calibrated using a density
strip.
Copyright © TWI Ltd
Copyright © TWI Ltd
Radiographic Sensitivity
Radiographic Sensitivity
IQI’s/Penetrameters are used to measure
radiographic sensitivity and the quality of the
radiographic technique used.
They are not used to measure the size of defects
detected.
7FE12
Step/hole type IQI
Wire type IQI
Copyright © TWI Ltd
Radiographic Sensitivity
Duplex type IQI
Copyright © TWI Ltd
Radiographic Sensitivity
Wire type IQI
Step/hole type IQI
Wire type IQI
Step/Hole type IQI
Copyright © TWI Ltd
Copyright © TWI Ltd
14‐2
Radiographic Techniques
Single Wall Single Image (SWSI)
Single Wall Single Image (SWSI)
 Film inside, source outside.
Single Wall Single Image (SWSI) panoramic
 Film outside, source inside (internal
exposure).
Film
Double Wall Single Image (DWSI)
 Film outside, source outside (external
exposure).
Film
Double Wall Double Image (DWDI)
 Film outside, source outside (elliptical
exposure).
IQI’s should be placed source side
Copyright © TWI Ltd
Single Wall Single Image Panoramic
Copyright © TWI Ltd
Double Wall Single Image (DWSI)
Film
 IQI’s are placed on the film side.
 Source inside film outside (single exposure).
Film
 IQI’s are placed on the film side.
 Source outside film outside (multiple exposure).
 This technique is intended for pipe diameters
over 100mm.
Copyright © TWI Ltd
Copyright © TWI Ltd
Double Wall Double Image (DWDI)




Film
IQI’s are placed on the source or film side.
Source outside film outside (multiple exposure).
A minimum of two exposures.
This technique is intended for pipe diameters
less than 100mm.
Copyright © TWI Ltd
Gamma Isotopes
Isotope
Iridium 192
Cobalt 60
Ytterbium 169
Thulium 170
Selenium 75
Typical thickness range
10 to 70 mm
> 50 mm
<10 mm
< 10 mm
10 to 40mm
Copyright © TWI Ltd
14‐3
Radiographic Testing
Gamma Isotopes Half Life
The half life of an isotope is the time taken for
an isotope to reduce its initial activity by a half.
After two half life's the activity is reduced to one
quarter of its initial activity. Isotopes are
normally replaced after 3 half life's.
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Cobalt 60
Iridium 192
Ytterbium 169
Selenium 75
5.3 years.
74 days.
32 days.
120 days.
Lead intensification screens (Pb)
 < 100 Kv’s None or up to 0.03mm thickness.
 100 to 250 KV’s up to 0.15mm thickness.
 > 250 KV’s / Ir192 up to 0.2mm thickness.
 Co60 0.25 to 0.7mm thickness.
Source Size
 Ir192 1.5 X 1.5 17Ci, 2.0 X 2.0 60Ci, 3 X 2 120Ci 4 X 4
300Ci.
Processing
 Development typically 4minutes at 20°C.
 Fixing typically around 2-4 minutes at 20°C.
Density typically 2 to 3.5.
Sensitivity typically 2% or less.
Copyright © TWI Ltd
Copyright © TWI Ltd
Radiographic Testing
Advantages
 Permanent record.
 Little surface
preparation.
 Defect identification.
 No material type
limitation.
 Not so reliant upon
operator skill.
 Thin materials.
Ultrasonic Testing
Disadvantages
 Expensive consumables.
 Bulky equipment.
 Harmful radiation.
 Defect require significant
depth in relation to the
radiation beam (not good
for planar defects).
 Slow results.
 Very little indication of
depths.
 Access to both sides
required.
Copyright © TWI Ltd
Copyright © TWI Ltd
Ultrasonic Testing
Main features
 Surface and sub-surface detection.
 This detection method uses high frequency sound
waves, typically above 2MHz to pass through a material.
 A probe is used which contains a piezo electric crystal to
transmit and receive ultrasonic pulses and display the
signals on a cathode ray tube or digital display.
 The actual display relates to the time taken for the
ultrasonic pulses to travel the distance to the interface
and back.
 An interface could be the back of a plate material or a
defect.
 For ultrasound to enter a material a couplant must be
introduced between the probe and specimen.
Copyright © TWI Ltd
Ultrasonic Testing
Pulse echo signals
A scan display
Compression probe
Digital
UT set
Checking the material thickness
Copyright © TWI Ltd
14‐4
Ultrasonic Testing
Defect
echo
Initial
pulse
Back wall
echo
Ultrasonic Testing
UT
set
A scan
display
Material Thk
Defect
0
Compression probe
10
20
30
40
50
Angle
probe
CRT display
Copyright © TWI Ltd
Copyright © TWI Ltd
Ultrasonic Testing
Probes Frequency Crystal Application
Initial
pulse
defect
Defect
echo
½ Skip
Full Skip
Defect
echo
0°
4 to 5 MHz
Twin
10mm
Lamination scanning,
weld scanning if cap
ground flush
45°
4 to 5 MHz
Single
10mm
Weld body scanning root
pass and plate thickness
above 15mm
60°
4 to 5 MHz
Single
10mm
Weld body scanning plate
thickness above 10mm
70°
4 to 5 MHz
Single
10mm
Weld body scanning all
plate thickness
0 10 20 30 40 50
CRT Display
Initial
pulse
defect
Ultrasonic Testing Probes
0 10 20 30 40 50
CRT Display
Copyright © TWI Ltd
Copyright © TWI Ltd
Ultrasonic Testing Calibration Blocks
Ultrasonic Testing Calibration Blocks
70o
0
100
25
V2 (A4) Block Thickness 12.5 or 20mm
0
V1/A2 Block
Copyright © TWI Ltd
100
200
V1 (A2) Block Thickness 25mm
Copyright © TWI Ltd
14‐5
Ultrasonic Testing
Advantages
 Rapid results.
 Both surface and
 Sub-surface detection.
 Safe.
 Capable of measuring the
depth of defects.
 May be battery powered.
 Portable.
Magnetic Particle Testing
Disadvantages
 Trained and skilled
operator required.
 Requires high operator
skill.
 Good surface finish
required.
 Defect identification.
 Couplant may
contaminate.
 No permanent record.
 Calibration Required.
 Ferritic material
(mostly).
Copyright © TWI Ltd
Copyright © TWI Ltd
Magnetic Particle Testing
Main features
 Surface and slight sub-surface detection.
 Relies on magnetization of component being tested.
 Only Ferro-magnetic materials can be tested.
 A magnetic field is introduced into a specimen being
tested.
 Methods of applying a magnetic field, yoke, permanent
magnet, prods and flexible cables.
 Fine particles of iron powder are applied to the test area.
 Any defect which interrupts the magnetic field, will
create a leakage field, which attracts the particles.
 Any defect will show up as either a dark indication or in
the case of fluorescent particles under UV-A light a
green/yellow indication.
Magnetic Particle Testing
Collection of ink
particles due to
leakage field
Electro-magnet
(yoke) DC or AC
Prods DC or AC
Copyright © TWI Ltd
Magnetic Particle Testing
Copyright © TWI Ltd
Magnetic Particle Testing
Alternatively to contrast
inks, fluorescent inks
may be used for greater
sensitivity.
A crack like
indication
These inks require a UVA light source and a
darkened viewing area to
inspect the component.
Crack like indication
Copyright © TWI Ltd
Copyright © TWI Ltd
14‐6
Magnetic Particle Testing
Typical sequence of operations to inspect a
weld
 Clean area to be tested.
 Apply contrast paint.
 Apply magnetisism to the component.
 Apply ferro-magnetic ink to the component
during magnatising.
 Interpret the test area.
 Post clean and de-magnatise if required.
Copyright © TWI Ltd
Magnetic Particle Testing
Advantages
 Simple to use.
 Inexpensive.
 Rapid results.
 Little surface
preparation required.
 Possible to inspect
through thin
coatings.
Penetrant Testing
Main features
 Detection of surface breaking defects only.
 This test method uses the forces of capillary
action.
 Applicable on any material type, as long they
are non porous.
 Penetrants are available in many different types:
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Magnetic ink composition
 Non-fluorescent ink between 1.25% to 3.5% by
volume.
 Fluorescent ink between 0.1% to 0.3% by volume.
Light requirements
 White light 500 Lux minimum.
 Black light 20 Lux or 1.0mW/cm2.
Permanent/electromagnets lifting capacity
 AC current 4.5 kg pole spacing 300mm or less.
 DC current 18 kg pole spacing above 75mm.
Prods
 6 amps/mm of spacing i.e. 200mm spacing =
1200 amps.
Copyright © TWI Ltd
Penetrant Testing
Disadvantages
 Surface or slight
sub-surface
detection only.
 Magnetic materials
only.
 No indication of
defects depths.
 Only suitable for
linear defects.
 Detection is required
in two directions.
Copyright © TWI Ltd

Magnetic Particle Testing
Copyright © TWI Ltd
Penetrant Testing
Step 1. Pre-cleaning
Ensure surface is very clean normally with the
use of a solvent.
Water washable contrast.
Solvent removable contrast.
Water washable fluorescent.
Solvent removable fluorescent.
Post-emulsifiable fluorescent.
Copyright © TWI Ltd
Copyright © TWI Ltd
14‐7
Penetrant Testing
Step 2. Apply penetrant
After the application, the penetrant is normally left on
the components surface for approximately 5-15
minutes (dwell time).
The penetrant enters any defects that may be present
by capillary action.
Penetrant Testing
Step 3. Clean off penetrant
The penetrant is removed after sufficient
penetration time (dwell time).
Care must be taken not to wash any penetrant
out/off any defects present.
Copyright © TWI Ltd
Copyright © TWI Ltd
Penetrant Testing
Penetrant Testing
Step 4. Apply developer
Step 5. Inspection/development time
After the penetrant has be cleaned sufficiently, a thin
layer of developer is applied.
The developer acts as a contrast against the penetrant
and allows for reverse capillary action to take place.
Inspection should take place immediately after the developer
has been applied.
Any defects present will show as a bleed out during
development time.
After full inspection has been carried out post cleaning is
generally required.
Copyright © TWI Ltd
Copyright © TWI Ltd
Penetrant Testing
Penetrant Testing
Test procedure
 Penetrant time 5-15 minutes.
 Development/inspection time 0-30 minutes.
Light requirements
 White light 500 Lux minimum.
 Black light 20 Lux or 1.0mW/cm2, below 20 Lux
ambient light.
 Inspectors should wait 5 minutes before
conducting inspection using fluorescent methods to
allow the eyes to become adapted to the
conditions.
Colour contrast penetrant
crack indication
Fluorescent penetrant
crack indication
Copyright © TWI Ltd
Temperature
 Between 10-50°C.
Copyright © TWI Ltd
14‐8
Penetrant Testing
Advantages
 Simple to use.
 Inexpensive.
 Quick results.
 Can be used on any nonporous material.
 Portability.
 Low operator skill
required.
Disadvantages
 Surface breaking defect
only.
 Little indication of depths.
 Penetrant may
contaminate component.
 Surface preparation
critical.
 Post cleaning required.
 Potentially hazardous
chemicals.
 Can not test unlimited
times.
 Temperature dependant.
Copyright © TWI Ltd
Any Questions
?
Copyright © TWI Ltd
NDT Specification Exercise
Please turn to appendix 2 in your course notes (A2-1),
here you will find four NDT reports accompanied by
five questions for each report relating to the NDT
method and referencing the TWI specification in most
cases.
There will be one correct answer for each question.
Note! Answers will be shown on screen using
PowerPoint section 14A after students have
completed the exercise.
Copyright © TWI Ltd
14‐9
Se ct ion 1 5
W e ldin g Con su m a ble s
15
W e ldin g Con su m a ble s
Welding consum ables are defined as all t hose t hings t hat are used up in t he
product ion of a w eld.
This list could include m any t hings including elect rical energy; howev er w e
norm ally refer t o w elding consum ables as t hose t hings used up by a part icular
welding process.
1 5 .1
M M A e le ct r ode s
MMA elect rodes can be cat egorised according t o t he t ype of cov ering t hey hav e
and consequent ly t he charact erist ics t hat it confers.
For C- Mn and low alloy st eels t her e ar e 3 gener ic t ypes of elect r odes:

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Cellulosic.
Rut ile.
Basic.
These generic nam es indicat e t he t ype of m iner al/ com pound t hat is dom inant in
t he covering.
1 5 .1 .1
Cove r e d e le ct r ode m a n uf a ct u r e
Elect r ode m anufact ur er s pr oduce elect rodes by :
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*
St raight ening and cut t ing core wire t o st andar d lengt hs ( t ypically 300, 350
and 450m m depending on elect rode classificat ion and diam et er) .
Making a dry m ix of powder ed com pounds/ m inerals ( precise levels of
addit ions depend on individual m anufact urer’s form ulat ions) .
Making a wet m ix by adding t he dry powder s t o a liquid binder.
Ext ruding t he covering ( concent rically) on t o t he cor e wire.
Hardening t he cov ering by drying t he elect rodes. *
Carr ying out bat ch t est s - as required for elect r ode cert ificat ion.
Packing t he elect r odes int o suit able cont ainers.
For low hydr ogen elect rodes t his is a high t em perat ur e bake - ≥~450ºC.


Vacuum pack ed elect rodes ar e packed in sm all quant it ies int o packaging
t hat is im m ediat ely vacuum sealed – t o ensure no m oist ure pick- up.
Elect r odes t hat need t o be r e- bak ed ar e pack ed int o st andard pack et s and
as t his m ay be som e t im e aft er baking, and t he packaging m ay not be
sealed, t hey do not r each t he end- user in a guarant eed low hydrogen
condit ion, t hey t her efore r equire r e- baking at a t ypical t em perat ur e of
350º C for appr oxim at ely 2 hours,
N ot e ! You should always follow t he m anufact ur er ’s r ecom m endat ions.
For individual bat ch cer t ificat ion t his will require t he m anufact ure of a t est pad
for chem ical analysis and m ay require m anufact ure of a t est w eld from which a
t ensile t est and Charpy V not ch t est pieces are t est ed.
WI S10- 30816
Welding Consum ables
15-1
Copyright © TWI Lt d
1 5 .1 .2
Ele ct r ode cove r ings
Cor e wires used for m ost C- Mn elect r odes, and som e low alloy st eel elect r odes,
are a v er y low C st eel* and it is t he form ulat ion of t he covering t hat det erm ines
t he com posit ion of t he deposit ed weld m et al and t he operat ing charact erist ics of
t he elect rode.
( * t ypically ~ 0.06% C, ~ 0.5% Mn)
The flux cov ering on an elect r ode is form ulat ed t o aid t he m anufact uring
process and t o provide a num ber of funct ions during welding.
The m aj or w elding funct ions are:
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1 5 .1 .3
Facilit at e arc ignit ion/ re- ignit ion and give ar c st abilisat ion.
Generat e gas for shielding t he arc and m olt en m et al from cont am inat ion by
air.
I nt eract wit h t he m olt en weld m et al t o give de- oxidat ion and flux im purit ies
int o t he slag t o cleanse/ refine t he m olt en weld m et al.
Form a slag for prot ect ion of t he hot w eld m et al from air cont am inat ion.
Provide elem ent s t o give t he weld m et al t he r equired m echanical propert ies.
Enable posit ional welding by m eans of slag form ers t hat fr eeze at
t em perat ur es abov e t he solidificat ion t em per at ure range of t he weld m et al.
I nspe ct ion point s for M M A consum a ble s
1. Size: Wire diam et er and lengt h.
2. Condit ion: Cracks, chips and concent ricit y.
3. Type ( specificat ion) : Cor r ect specificat ion/ code.
E 46 3 B
Check s should also be m ade t o ensur e t hat ba sic e le ct r ode s have been
t hrough t he cor r ect pr e - u se pr oce du r e . Having been baked t o t he cor rect
t em perat ur e ( t ypically 300- 350°C) for 1 hou r and t hen held in a holding oven
at 1 5 0 °C befor e being issued t o t he w elders in h e a t e d qu iv e r s. Most elect r ode
flux coat ings will det eriorat e rapidly when dam p and care should be t aken t o
inspect st orage facilit ies t o ensur e t hat t hey are adequat ely dry , and t hat all
elect r odes ar e st ored in condit ions of cont rolled t em perat ur e and hum idit y.
WI S10- 30816
Welding Consum ables
15-2
Copyright © TWI Lt d
1 5 .2
Ce llu losic e le ct r ode s
Cellulose is t he principal subst ance in t his t ype of elect rode and com prising
t ypically ~ 40% of t he flux const it uent s.
Cellulose is an organic m at erial ( nat urally occurring) such as cot t on and wood,
but it is wood pulp t hat is t he principal source of cellulose used in t he
m anufact ure of elect rode cov erings.
The m ain charact erist ics of cellulosic elect rodes are:








1 5 .2 .1
Cellulose br eaks down during welding and produces carbon m onoxide and
dioxide and hydr ogen.
Hydr ogen provides part of t he gas shielding funct ion and gives a relat ively
high arc v olt age.
The high arc volt age gives t he elect rode a hard and forceful arc wit h good
penet rat ion/ fusion abilit y.
The v olum e of slag form ed is r elat ively sm all.
Cellulosic elect rodes cannot be baked during m anufact ure or before welding
because t his would dest roy t he cellulose; t he m anufact uring procedure is t o
harden t he coat ing by drying ( t ypically at 70- 100º C) .
Because of t he high hydrogen levels t her e is always som e risk of H cracking
which requires cont r ol m easur es such as hot - pass w elding t o facilit at e t he
rapid escape of hydrogen.
Because of t he risk of H cracking t here are lim it s on t he st rengt h/
com posit ion and t hickness of st eels on which t hey can be used ( elect rode
are m anufact ur ed in classes E60xx , E70xx , E80xx and E90xx but bot h lower
st rengt h grades t end t o be t he m ost com m only used) .
High t oughness at low t em perat ur es cannot be consist ent ly achieved fr om
t his t ype of elect r ode ( t ypically only down t o about - 20º C) .
Applica t ions of ce llulosic e le ct r ode s
Cellulosic elect rodes have charact erist ics t hat enable t hem t o be used for
vert ical- down welding at fast t rav el speed but wit h low risk of lack- of- fusion
because of t heir forceful arc.
The niche applicat ion for t his t ype of elect r ode is girt h seam welding of large
diam et er st eel pipes for overland pipelines ( Tr ansco ( BGAS) P2, BS 4515 and
API 1104 applicat ions) . No ot her t ype of elect r ode has t he abilit y t o allow root
pass w elding at high speed and st ill give good root penet rat ion when t he root
gap is less t han ideal.
Because of t heir penet r at ion abilit y t hese elect r odes hav e also found applicat ion
on oil st orage t anks – for v ert ical and circum ferent ial seam welding of t he
upper/ t hinner cour ses for which pr eparat ions wit h large root faces or squar e
edge pr eparat ions are used.
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Copyright © TWI Lt d
1 5 .3
Ru t ile e le ct r ode s
Rut ile is a m ineral t hat consist s of about 90% t it anium dioxide ( TiO 2 ) and is
present in C and C- Mn st eel rut ile elect r odes at t ypically ~ 50% .
Charact erist ics of rut ile elect r odes ar e:







They hav e a ver y sm oot h and st able arc and produce a r elat ively t hin slag
cov ering t hat is easy t o rem ov e.
They give a sm oot h w eld profile.
They ar e r egarded as t he m ost user- friendly of t he various elect rode t ypes.
They have relat ively high com bined m oist ure cont ent and because t hey
cont ain t ypically up t o ~ 10% cellulose t hey cannot be baked and
consequent ly t hey do not give a low H w eld deposit .
Because of t he risk of cracking t hey ar e not designed for w elding of high
st rengt h or t hick sect ion st eel.
( Alt hough elect rodes ar e m anufact ur ed in classes E60xx , E70x x, E80x x t he
E60xx grade is by far t he m ost com m only used) .
They do not give high t oughness at low t em perat ur es ( t ypically only down
t o about - 20º C) .
The abov e list ed charact erist ics m ean t hat t his t ype of elect r ode is used for
general- purpose fabricat ion of unalloyed, low st rengt h st eels in relat ively t hin
sections (typically ≤ ~13mm).
1 5 .3 .1
Rut ile e le ct r ode v a r ia nt s
By adding iron powder t o t he cov ering a range of t hick- coat ed elect r odes hav e
been produced in order t o enhance pr oduct ivit y.
Such elect r odes give w eld deposit s t hat weigh bet ween ~ 135 and 190% of t heir
core wire w eight and so r efer r ed t o as high recov er y elect rodes, or m or e
specifically for exam ple a 170% recovery elect r ode.
The w eld deposit fr om such elect r odes can be r elat ively large and fluid and t his
rest rict s welding t o t he flat posit ion and for st anding fillet s for elect r odes wit h
t he highest recovery rat es.
I n all ot her r espect s t hese elect r odes have t he charact erist ics list ed for st andard
rut ile elect rodes.
1 5 .4
Ba sic e le ct r ode s
Basic elect rodes ar e so nam ed because t he cov ering is m ade wit h a high
proport ion of basic m inerals/ com pounds ( alkaline com pounds) , such as calcium
carbonat e ( CaCO 3 ) , m agnesium carbonat e ( MgCO 3 ) and calcium fluoride
( CaF2 ) .
A fully basic elect rode cov ering will be m ade up wit h about 60% of t hese basic
m inerals/ com pounds.
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Copyright © TWI Lt d
Charact erist ics of basic elect r odes ar e:




The basic slag t hat for m s when t he cov ering m elt s react s wit h im purit ies,
such as sulphur and phosphorus, and also reduces t he ox ygen cont ent of
t he weld m et al by de- ox idat ion.
The r elat ively clean weld m et al t hat is deposit ed gives a very significant
im provem ent in weld m et al t oughness ( C- Mn elect rodes wit h Ni addit ions
can give good t oughness down t o - 90°C) .
They can be baked at relat ively high t em perat ures wit hout any of t he
com pounds pr esent in t he cov ering being dest r oy ed, t her eby giving low
m oist ure cont ent in t he cov ering and low hydrogen levels in weld m et al.
I n order t o m aint ain t he elect r odes in a low hydrogen condit ion t hey need t o
be pr ot ect ed fr om m oist ure pick- up.
฀
฀


By m eans of baking befor e use ( t ypically at ~ 350°C) , t ransfer ring t o a
holding oven ( t ypically at ~ 120°C) and issued in sm all quant it ies
and/ or using heat ed quivers ( ‘port able ovens’) at t he w ork st at ion
( t ypically ~ 70°.
By use of vacuum pack ed elect rodes t hat do not need t o be re- bak ed
befor e use.
Basic slag is relat ively viscous and t hick which m eans t hat elect rode
m anipulat ion requires m or e skill and should be used wit h a short arc t o
m inim ise t he risk of por osit y.
The sur face pr ofile of weld deposit s from basic elect rodes t ends t o be
conv ex and slag rem oval requires m or e effort .
M e t a l pow de r e le ct r ode s cont ain an addit ion of m et al powder t o t he flux
coat ing t o increase t he m axim um perm issible welding current lev el. Thus, for a
given elect rode size, t he m et al deposit ion rat e and efficiency ( percent age of t he
m et al deposit ed) ar e incr eased com par ed wit h an elect r ode cont aining no iron
powder in t he coat ing. The slag is norm ally easily rem ov ed. I r on powder
elect r odes are m ainly used in t he flat and H/ V posit ions t o t ake advant age of
t he higher deposit ion rat es. Efficiencies as high as 130- 140% can be achieved
for rut ile and basic elect r odes wit hout m arked det eriorat ion of t he arcing
charact erist ics but t he arc t ends t o be less for ceful which reduces bead
penet rat ion.
1 5 .4 .1
Applica t ions of ba sic e le ct r ode s
Basic elect r odes have t o be used for all applicat ions t hat require good fract ur e
t oughness at t em perat ures below ~ - 20°C.
To avoid t he risk of hydrogen cracking basic elect rodes have t o be used for
welding hardenable st eels ( m ost C- Mn and all low alloy st eels) and for m ost
st eels when t he j oint t hickness is gr eat er t han about 15m m .
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Welding Consum ables
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Copyright © TWI Lt d
1 5 .5
Cla ssif ica t ion of e le ct r ode s
Nat ional st andards for elect rodes t hat are used for w elding are:



BS EN I SO 2560 - Covered elect rodes for m anual m et al arc welding of nonalloy and fine grain st eels.
AWS A5.1 - Specificat ion for carbon st eel elect rodes for shielded m et al arc
welding.
AWS A5.5 - Specificat ion for low- alloy st eel elect rodes for shielded m et al arc
welding.
Elect r ode classificat ion is based on t est s specified by t he st andard on weld
deposit s m ade wit h each t ype of cov ered elect r ode. The st andards require
chem ical analysis and m echanical t est s and elect rode m anufact ur ers t end t o
dual cert ify elect rodes, wher ev er possible, t o bot h t he European and Am erican
st andards
1 5 .5 .1
BS EN I SO 2 5 6 0
BS EN I SO 2560 - Cov ered elect r odes for m anual m et al arc welding of non- alloy
and fine grain st eels ( see Figure 15.1) .
This is t he designat ion t hat m anufact urer s print on t o each elect rode so t hat it
can be easily ident ified. The classificat ion is split int o t wo sect ions:
Com pu lsor y se ct ion - t his includes t he sym bols for:





Type of pr oduct .
St rengt h.
I m pact pr opert ies.
Chem ical com posit ion.
Type of elect rode cov ering.
Opt ion a l se ct ion - t his includes t he sy m bols for:




Weld m et al recov ery.
The t ype of cur rent .
The w elding posit ions.
The hydrogen cont ent .
The designat ion, com pulsor y ( st r engt h, t oughness and coat ing including any
light alloying elem ent s) m ust be ident ified on t he elect rode, how ev er t he
opt iona l ( posit ion, hydrogen levels et c are not m a nda t or y and m ay not be
shown on all elect rodes.
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Welding Consum ables
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Copyright © TWI Lt d
Figur e 1 5 .1 The e le ct r ode cla ssifica t ion syst e m of BS EN I SO 2 5 6 0 .
1 5 .5 .2
AW S A5 .1 / 5 .1 M : 2 0 0 3
AWS A5.1/ 5.1M: 2003 - Specificat ion for carbon st eel elect rodes for shielded
m et al arc w elding ( see Figure 15.2) .
This specificat ion est ablishes t he requirem ent s for classificat ion of cov er ed
elect r odes wit h carbon st eel cor es for MMA welding. Requirem ent s include
m echanical propert ies of w eld m et al; weld m et al soundness; and usabilit y of
elect r odes.
Requirem ent s for chem ical com posit ion of t he weld m et al, m oist ure cont ent of
low hydrogen elect rodes, st andard sizes and lengt hs, m arking, m anufact uring
and packaging are also included.
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Welding Consum ables
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Copyright © TWI Lt d
A guide t o t he use of t he st andard is given in an appendix. Opt ional
supplem ent ary requirem ent s include im proved t oughness and duct ilit y, lower
m oist ure cont ent s and diffusible hydrogen lim it s.
The AWS classificat ion syst em has m andat or y and opt ional designat ors and
requires t hat bot h t he m andat ory classificat ion designat ors and any opt ional
designat ors be print ed on each elect r ode. The last t wo digit s of t he m andat ory
part of t he classificat ion are used t o designat e t he t ype of elect r ode
coat ing/ covering and ex am ples of som e of t he m or e widely used elect r odes are
shown below.
Ta ble 1 5 .1 Ex a m ple s of som e of t he com m only use d AW S A5 .1 e le ct r ode s.
AW S A5 .1
cla ssifica t ion
E6010
E6011
E6012
E6013
E7014
E7015
E7016
E7018
E7024
Te nsile st r e n gt h, N / m m 2
414
482
Type of coa t in g
Cellulosic
Cellulosic
Rut ile
Rut ile
Rut ile, iron powder
Basic
Basic
Basic, iron powder
Rut ile high recov ery
Typical elect rode t o AWS A5.1
D e sign a t e s: An
elect r ode
D e sign a t e s: The t ensile
st rengt h ( m in.) in PSI of
t he weld m et al
D e sign a t e s: The w elding
posit ion t he t ype of cov ering
and t he kind of curr ent
Figur e 1 5 .2 M a n da t or y cla ssifica t ion de signa t or s.
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Welding Consum ables
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Copyright © TWI Lt d
Ta ble 1 5 .1 Com m on e le ct r ode s t ha t a r e cla ssifie d t o BS EN I SO 2 5 6 0 & AW S
A5 .1 / 5 .5 .
Ge n e r a l de scr ipt ion
BS EN I SO 2 5 6 0
AW S A5 .1 / 5 .5
Ce llu losic e le ct r ode s
E 38 3 C 21
E6010
( For v ert ical- down w elding
‘St ov epipe welding’
of pipeline girt h w elds)
E 42 3 Z C 21
E7010- G
E 46 3 Z C 21
E8010- G
E 42 3 C 25
E7 0 1 0 - P 1 *
E 46 4 1Ni C 25
E8 0 1 0 - P 1 *
*
P =
specially
elect r odes
E 38 2 R 12
Ru t ile e le ct r ode s
designat ed
piping
E6013
( For general purpose fabricat ion of low
st rengt h st eels – can be used for all
posit ions except vert ical- down)
E 42 0 R 12
E6013
H e a vy coa t e d r u t ile e le ct r ode s
E 42 0 RR 13
E6013
( I r on- powder elect rodes)
E 42 0 RR 74
E7024
Ba sic e le ct r ode s
E 42 2 B 12 H10
E7016
( For higher st rengt h st eels,
t hicker sect ion st eels w her e t here
is risk of H cracking; for all
applicat ions r equiring good
fract ur e t oughness)
E 42 4 B 32 H5
E7018
E 46 6 Mn1Ni B 12 H5
E 7016- G
E 55 6 Mn1Ni B 32 H5
E8018- C1
E 46 5 1Ni B 45 H5*
E8018- G
( For higher pr oduct ivit y welding
for general fabricat ion of low
st rengt h st eels – can generally
only be used for downhand or
st anding fillet welding)
E9018- G
E10018- G
* Vert ical- down low H elect r odes
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Welding Consum ables
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Copyright © TWI Lt d
1 5 .6
TI G fille r w ir e s
Filler wires m anufact ur ed for TI G w elding have com posit ions very sim ilar t o
t hose of base m at erials. How ev er, t hey m ay cont ain ver y sm all addit ions of
elem ent s t hat will com bine wit h oxygen and nit rogen as a m eans of scavenging
any cont am inant s from t he surface of t he base m at erial or from t he
at m osphere.
For m anual TI G, t he wires are m anufact ur ed t o t he BS EN I SO 14341 and are
provided in 1m lengt hs ( t ypically 1.2, 1.6, and 2.4m m diam et er) and for
ident ificat ion have flat t ened ends on which is st am ped t he wire designat ion ( in
accordance wit h a part icular st andard) and, for som e gr ades, a bat ch num ber.
TI G consum able ident ificat ion is st am ped at t he end of t he wire.
For m aking precision root runs for pipe but t welds ( part icularly for aut om at ed
TI G welding) consum able insert s can be used t hat are m ade from m at erial t he
sam e as t he base m at er ial, or ar e com pat ible wit h it .
For sm all diam et er pipe, t he insert m ay be a ring but for larger diam et er pipe
an insert of t he appropr iat e diam et er is m ade from shaped st rip/ wire, exam ples
of which ar e shown below.
1 5 .6 .1
TI G sh ie lding ga se s
Pure argon is t he shielding gas t hat is used for m ost applicat ions and is t he
preferr ed gas for TI G welding of st eel and gas flow rat es are t ypically ~ 8- 12
lit res/ m in for shielding.
The shielding gas not only prot ect s t he arc and weld pool but also is t he
m edium required t o est ablish a st able arc by being easy t o ionise. A st able arc
cannot be est ablished in air and hence t he w elder w ould not be able t o weld if
t he shielding gas wer e not swit ched on.
Argon wit h a helium addit ion – t ypically ~ 30% m ay be used when a hot t er ar c
is needed such as when welding m et als wit h high t herm al conduct ivit y, such as
copper/ copper alloys or t hicker sect ion alum inium / alum inium alloys.
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Ther e ar e som e circum st ances when special shielding gases ar e beneficial, for
exam ple:
Ar + 3- 5% H for aust enit ic st ainless st eels and Cu- Ni alloys.
Ar + ~ 3% N for duplex st ainless st eels.
1 5 .6 .2
TI G ba ck - pur gin g
For m ost m at erials, t he underside of a w eld root bead needs t o be pr ot ect ed by
an inert gas ( a back- pur ge) – t ypically ~ 6- 8 lit res/ m in during welding.
For C steels and low alloy steels with total alloying additions ≤2.5% it may not
always be necessary t o use a back- purge but for higher alloyed st eels and m ost
ot her m at erials t here m ay be excessive oxidat ion – and risk of lack of fusion if it
is not used.
1 5 .7
M I G/ M AG f ille r w ir e s
Solid filler wires m anufact ured for MI G/ MAG generally have chem ical
com posit ions t hat have been form ulat ed for part icular base m at erials and t he
wires have com posit ions sim ilar t o t hese base m at erials. Solid wires for welding
st eels wit h act ive shielding gases ar e deoxidised wit h m anganese and silicon t o
avoid por osit y. Ther e m ay also be t it anium and alum inium addit ions.
Mild st eel filler wires ar e available wit h different levels of deoxidant s, k nown as
double or t riple de- oxidised wires. Mor e highly deoxidised wires are m or e
expensive but ar e m or e t olerant of t he plat e surface condit ion, eg m ill scale,
surface rust , oil, paint and dust . There m ay, t her efor e, be a reduct ion in t he
am ount of cleaning of t he st eel befor e welding.
These deoxidiser addit ions yield a sm all am ount of glassy slag on t he surface of
t he weld deposit , com m only refer red t o as silica deposit s. These sm all pocket s
of slag are easily rem ov ed wit h light brushing; but when galvanising or paint ing
aft er w elding, it is necessar y t o use shot blast ing.
During welding, it is com m on pract ice t o w eld ov er t hese sm all islands since
t hey do not r epr esent a t hick slag, and t hey usually spall off during t he
cont ract ion of t he weld bead. How ev er , when m ult ipass welding, t he slag level
m ay build up t o an unaccept able level causing weld defect s and unr eliable arc
st art ing.
St eel wires usually have a flash coat ing of copper t o im prove curr ent pick- up
and t o ext end t he shelf life of t he wire. However, t he copper coat ing can
som et im es flake off and be drawn int o t he liner and wire feed m echanism ,
part icularly if t here is m isalignm ent in t he wire feed syst em . This m ay cause
clogging and errat ic wire feed.
Uncoat ed wires are available as an alt ernat ive, alt hough elect rical cont act m ay
not be as good as wit h copper- coat ed wires, and cont act t ip operat ing
t em perat ur es m ay be higher.
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Copyright © TWI Lt d
Som e t ypical St andards for specificat ion of st eel wire consum ables are:
BS EN I SO 1 4 3 4 1
Welding consum ables - Wire elect rodes and deposit s for gas shielded m et al arc
welding of non- alloy and fine grain st eels - Classificat ion.
BS EN I SO 1 6 8 3 4
Welding consum ables - Wire elect rodes, wires, r ods and deposit s for gas
shielded m et al arc welding of high st rengt h st eels - Classificat ion.
Wire sizes ar e t ypically in t he range 0.6- 2.4m m diam et er but t he m ost
com m only used sizes are 0.8, 1, 1.2 and 1.6m m and provided on layer w ound
spools for consist ent feeding.
Spools should be labelled t o show t he classificat ion of t he wire and it s’
diam et er.
Flux- cored and m et al- cored wires ar e also used ext ensively alt hough t he
process is t hen referr ed t o as FCAW ( flux- cored ar c welding) and M CAW
( m et al cor ed arc welding)
1 5 .7 .1
M I G/ M AG ga s shie lding
For non- ferr ous m et als and t heir alloys ( such as Al, Ni and Cu) an inert
shielding gas m ust be used. This is usually eit her pure argon or an argon rich
gas wit h a helium addit ion.
The use of a fully inert gas is t he reason why t he process is also called M I G
welding ( m et al inert gas) and for pr ecise use of t erm inology t his nam e should
only be used when r efer ring t o t he welding of non- ferr ous m et als.
The addit ion of som e helium t o argon gives a m or e uniform heat concent rat ion
wit hin t he arc plasm a and t his affect s t he shape of t he weld bead pr ofile.
Argon- helium m ixt ures effect ively give a hot t er arc and so t hey are beneficial
for w elding t hicker base m at erials t hose wit h higher t herm al conduct ivit y eg
copper or alum inium .
For w elding of st eels – all grades, including st ainless st eels – t here needs t o be
a cont rolled addit ion of oxygen or carbon dioxide in order t o generat e a st able
arc and give good droplet wet t ing. Because t hese addit ions react wit h t he
m olt en m et al t hey are referr ed t o as act ive gases and hence t he nam e M AG
welding ( m et al a ct ive gas) is t he t echnical t erm t hat is use when r eferring t o
t he welding of st eels.
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Copyright © TWI Lt d
The percent age of carbon dioxide ( CO 2 ) or oxy gen depends on t he t ype of st eel
being welded and t he m ode of m et al t ransfer being used – as indicat ed below:



100% CO 2
For low carbon st eel t o give deeper penet rat ion ( Figure 15.3) and fast er
welding t his gas prom ot es globular droplet t ransfer and gives high levels of
spat t er and welding fum e.
Argon + 15 t o 25% CO 2
Widely used for carbon and som e low alloy st eels ( and FCAW of st ainless
st eels) .
Argon + 1 t o 5% O 2
Widely used for st ainless st eels and som e low alloy st eels.
Figur e 1 5 .3 Effe ct s of shie lding ga s com posit ion on w e ld pe ne t r a t ion a n d
pr ofile .
Figur e 1 5 .4 Act ive shie lding ga s m ix t ur e s f or M AG w e lding of ca r bon , ca r bonm a nga ne se a n d low a lloy st e e ls.
Blue is a cooler gas m ix t ure; r ed is a hot t er m ixt ure.
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Copyright © TWI Lt d
Gas m ixt ures - helium in place of argon gives a hot t er arc, m or e fluid weld pool
and bet t er w eld profile. These quat ernar y m ixt ures perm it higher welding
speeds, but m ay not be suit able for t hin sect ions.
St a in le ss st e e ls
Aust enit ic st ainless st eels are t ypically welded wit h argon- CO 2 / O 2 m ixt ures for
spray t ransfer, or argon- helium - CO 2 m ixt ures for all m odes of t ransfer. The
oxidising pot ent ial of t he m ixt ures are k ept t o a m inim um ( 2- 2.5% m axim um
CO 2 cont ent ) in order t o st abilise t he arc, but wit h t he m inim um effect on
corr osion perform ance. Because aust enit ic st eels have a high t herm al
conduct ivit y, t he addit ion of helium helps t o avoid lack of fusion defect s and
ov er com e t he high heat dissipat ion int o t he m at erial. Helium addit ions are up t o
85% , com pared wit h ~ 25% for m ixt ures used for carbon and low alloy st eels.
CO 2 - cont aining m ixt ures are som et im es av oided t o elim inat e pot ent ial carbon
pick- up.
Figur e 1 5 .5 Act ive shie lding ga s m ix t ur e s for M AG w e lding of st a inle ss st e e ls.
Blue is a cooler gas m ix t ure; r ed is a hot t er m ixt ure.
For m art ensit ic and duplex st ainless st eels, specialist advice should be sought .
Som e Ar- He m ixt ures cont aining up t o 2.5% N 2 are available for w elding duplex
st ainless st eels.
Light alloys, eg alum inium and m agnesium , and copper and nickel and t heir
alloys
I nert gases are used for light alloys and alloys t hat are sensit ive t o oxidat ion.
Welding grade inert gases should be purchased rat her t han com m ercial purit y
t o ensure good w eld qualit y.
Ar gon
Argon can be used for alum inium because t her e is sufficient surface oxide
available t o st abilise t he arc. For m at erials t hat are sensit ive t o oxygen, such as
t it anium and nickel alloys, ar c st abilit y m ay be difficult t o achieve wit h inert
gases in som e applicat ions.
The densit y of argon is approxim at ely 1.4 t im es t hat of air. Therefor e, in t he
downhand posit ion, t he relat ively heavy argon is very effect ive at displacing air.
A disadvant age is t hat when wor king in confined spaces, t her e is a risk of argon
building up t o dangerous levels and asphy xiat ing t he w elder.
WI S10- 30816
Welding Consum ables
15-14
Copyright © TWI Lt d
Ar gon- h e lium m ix t u r e s
Argon is m ost com m only used for MI G w elding of light alloys, but som e
advant age can be gained by t he use of helium and argon/ helium m ixt ures.
Helium possesses a higher t herm al conduct ivit y t han argon. The hot t er weld
pool produces im prov ed penet rat ion and/ or an increase in welding speed. High
helium cont ent s give a deep broad penet r at ion profile, but produce high spat t er
levels. Wit h less t han 80% argon, a t rue spr ay t ransfer is not possible. Wit h
globular- t ype t ransfer, t he w elder should use a 'buried' arc t o m inim ise spat t er .
Arc st abilit y can be pr oblem at ic in helium and argon- helium m ixt ures, since
helium raises t he ar c volt age, and t her efore t here is a larger change in arc
volt age wit h respect t o arc lengt h. Helium m ixt ures r equire higher flow rat es
t han argon shielding in order t o provide t he sam e gas pr ot ect ion.
Ther e is a reduced risk of lack of fusion defect s when using argon- helium
m ixt ures, part icularly on t hick sect ion alum inium . Ar- He gas m ixt ures will offset
t he high heat dissipat ion in m at erial over about 3m m t hickness.
Figur e 1 5 .6 I ne r t shie lding ga s m ix t u r e s for M I G w e lding of a lum inium ,
m a gne sium , t it a niu m , n ick e l a nd coppe r a lloys.
Blue is a cooler gas m ix t ure; r ed is a hot t er m ixt ure.
A sum m ary t able of shielding gases and m ixt ures used for differ ent base
m at erials is given in Table 15.2.
WI S10- 30816
Welding Consum ables
15-15
Copyright © TWI Lt d
Sum m a r y
Ta ble 1 5 .2 Shie lding ga s m ix t ur e s for M I G/ M AG w e lding – sum m a r y
Metal
Carbon
st eel
St ainless
st eels
Alum inium ,
copper,
nickel,
t it anium
alloys
WI S10- 30816
Welding Consum ables
Shie lding
ga s
ArgonCO 2
Re a ct ion
be h a viour
Slight ly
oxidising
ArgonO2
Slight ly
oxidising
Argonhelium CO 2
Slight ly
oxidising
CO 2
Oxidising
He- ArCO 2
Slight ly
oxidising
Argon- O 2
Slight ly
oxidising
Argon
I nert
Argonhelium
I nert
15-16
Cha r a ct e r ist ics
I ncreasing CO 2 cont ent gives hot t er
arc, im prov ed ar c st abilit y, deeper
penet rat ion, t r ansit ion from fingert ype t o bowl- shaped penet rat ion
profile, m ore fluid weld pool giving
flat t er weld bead wit h good wet t ing,
increased spat t er lev els, bet t er
t oughness t han CO 2 . Min 80% argon
for axial spray t ransfer. Generalpurpose m ixt ure:
argon- 10- 15% CO 2 .
St iffer ar c t han Ar- CO 2 m ixt ures
m inim ises undercut t ing, suit ed t o
spray t ransfer m ode, lower
penet rat ion t han Ar- CO 2 m ixt ures,
'finger'- t ype w eld bead penet rat ion
at high curr ent levels. Generalpurpose m ixt ure: argon- 3% CO 2 .
Subst it ut ion of helium for argon
gives hot t er arc, higher arc volt age,
m or e fluid weld pool, flat t er bead
profile, m ore bowl- shaped and
deeper penet rat ion profile and
higher w elding speeds, com pared
wit h Ar- CO 2 m ixt ures. High cost .
Arc volt ages 2- 3V higher t han ArCO 2 m ixt ures, best penet rat ion,
higher w elding speeds, dip t ransfer
or buried arc t echnique only, narr ow
wor king range, high spat t er lev els,
low cost .
Good arc st abilit y wit h m inim um
effect on corr osion r esist ance
( carbon pickup) , higher helium
cont ent s designed for dip t ransfer ,
lower helium cont ent s designed for
pulse and spray t ransfer . Generalpurpose gas: Ar- 40- 60% He- 2% CO 2 .
Spray t ransfer only, m inim ises
undercut t ing on heavier sect ions,
good bead profile.
Good arc st abilit y, low spat t er, and
general- purpose gas. Tit anium
alloys r equire inert gas backing and
t railing shields t o pr ev ent air
cont am inat ion.
Higher heat input offset s high heat
dissipat ion on t hick sect ions, lower
risk of lack of fusion defect s, higher
spat t er and higher cost t han argon.
Copyright © TWI Lt d
1 5 .8
SAW fille r w ir e s
Filler wires for SAW are m ade t o AWS and EN st andards and t he m ost
com m only used sizes are 2.4, 3.2, 4 and 5m m diam et er and ar e av ailable for
welding a wide range of st eels and som e non- fer rous applicat ions, t hey hav e
com posit ions sim ilar t o t he base m at erial but for cert ificat ion st andards require
flux/ wire w eld m et al deposit s t o be m ade for analysis and t est ing as r equired
1 5 .8 .1
SAW flu x t ype s
Fluxes can be cat egorised int o t wo t ypes, nam ely fused and agglom erat ed
( agglom erat ed fluxes are som et im es called bonded fluxes – part icularly in t he
USA) .
Fuse d f lux
These t ypes are m anufact ured by m ixing cert ain suit able m inerals/
com pounds, fusing t hem t oget her , crushing t he solid m ass and t hen sieving t he
crushed m ass t o r ecov er granules wit hin a part icular size range.
Fused fluxes have t he following charact erist ics/ propert ies:




Cont ain a high proport ion of silica ( up t o ~ 60% ) and so t he flux granules
have sim ilar in appearance t o crushed glass – irregular shaped and hard and have a sm oot h, and slight ly shiny, surface.
During re- circulat ion t hey have good r esist ance t o br eaking down int o fine
part icles – referr ed t o as fines.
Hav e v ery low m oist ure cont ent as m anufact ured and does not absorb
m oist ure during exposure and so t hey should always give low hydrogen
weld m et al.
Give w elds beads wit h good surface finish and profile and de- slag easily.
The m ain disadvant age of fused fluxes is t hat t he com pounds t hat give deoxidat ion cannot be added so t hat welds have high oxygen cont ent and so st eel
weld m et al does not have good t oughness at sub- zero t em perat ur es.
WI S10- 30816
Welding Consum ables
15-17
Copyright © TWI Lt d
Agglom e r a t e d flux
This is m anufact ured by m ixing fine powder ed m inerals/ com pounds, adding a
wet binder and furt her m ixing t o form flux granules of t he required size. These
are dried/ baked t o r em ov e m oist ure, siev ed and packaged in sealed cont ainers
t o ensure t hey ar e in low hydr ogen condit ion when supplied t o t he user .
Som e of t he m inerals/ com pounds used in t hese fluxes cannot be subj ect ed t o
t he high t em perat ur es r equired t o m ak e fused fluxes because t hey would break
down and lose t he propert ies t hat are needed during welding.
Agglom erat ed fluxes have t he following charact erist ics:




Granules t end t o be m ore spherical and have a dull/ m at t finish.
Granules ar e consist of fine powder s, w eakly held t oget her, and so are quit e
soft and easily be brok en down int o fine powders during handling/
re- circulat ion.
Som e of t he com pounds and t he binder it self, will t end t o absorb m oist ure
from t he at m ospher e if left exposed and a cont rolled handling procedure* is
essent ial.
The slag is less fluid t han t hose generat ed by fused fluxes and t he weld
bead pr ofile t ends t o be m ore convex and m or e effort is r equired t o r em ov e
t he slag.
* Agglom erat ed fluxes are sim ilar t o fluxes used for basic cov er ed elect r odes
and suscept ible t o m oist ure pick- up when t hey are cold and left exposed.
A t ypical cont rolled handling pract ice is t o t ransfer flux from t he m anufact ur er ’s
drum / bag t o a heat ed silo ( ~ 120- 150°C) . This act s like t he holding ov en for
basic elect r odes.
Warm flux is t ransfer red t o t he flux hopper on t he m achine ( usually unheat ed)
and at t he end of a shift or when t her e is t o be an int errupt ion in welding, t he
hopper flux should be t r ansferr ed t o t he silo.
The part icular advant age of agglom erat ed fluxes is t her e abilit y t o give weld
m et als wit h low oxygen cont ent and t his enables st eel weld m et al t o be
produced wit h good sub- zero t oughness.
WI S10- 30816
Welding Consum ables
15-18
Copyright © TWI Lt d
1 5 .8 .2
SAW flux ba sicit y inde x
Fluxes are oft en referr ed t o as having a cert ain basicit y or basicit y index ( BI ) .
The BI indicat es t he flux form ulat ion according t o t he rat io of basic com pounds
t o acid com pounds and is used t o give an indicat ion of flux/ weld react ion and
can be int erpret ed as follows:




A flux wit h a BI = 1 has an equal rat io of basic and acid com pounds and
t hus is neit her basic nor acid but said t o be n e u t r a l.*
A flux wit h BI > 1 has ba sic charact erist ics; fully basic fluxes have BI of ~ 3~ 3.5.
A flux wit h BI < 1 has acid charact erist ics.
Fused and agglom erat ed fluxes are m ixed t o produce fluxes referr ed t o as
sem i- basic.
* I n t he USA it is cust om ary t o use t he t erm s neut ral t o indicat e t hat t he flux
has no significant influence on t he com posit ion by t ransfer of elem ent s from
flux t o weld pool and act ive t o indicat e t hat t he flux does t ransfer som e
elem ent s.
Fused fluxes have acid charact erist ics and agglom erat ed fluxes have basic
charact erist ics.
Alt hough t here are EN and AWS st andards for flux classificat ion, it is com m on
UK pract ice t o order fluxes by m anufact urer nam e and use t his nam e on WPSs.
WI S10- 30816
Welding Consum ables
15-19
Copyright © TWI Lt d
Welding Consumables
Welding consumables are any products that are
used up in the production of a weld.
Welding consumables may be
 Covered electrodes, filler wires and electrode
wires.
 Shielding or oxy-fuel gases.
 Separately supplied fluxes.
 Fusible inserts.
Welding Consumables
Section 15
Copyright © TWI Ltd
Welding Consumable Standards
MMA (SMAW)
 BS EN ISO 2560:
 AWS A5.1:
 AWS A5.4:
 AWS A5.5:
Steel electrodes.
Non-alloyed steel electrodes.
Chromium electrodes.
Alloyed steel electrodes.
Copyright © TWI Ltd
Welding Consumable Standards
SAW
 BS 4165:
 BS EN ISO 14171:
 BS EN ISO 14174:
 AWS A5.17:
Wire and fluxes.
Wire electrodes.
Fluxes.
Wires and fluxes.
MIG/MAG (GMAW) TIG (GTAW)
 BS EN ISO 14343:
Filler wires.
 BS EN ISO 14341:
Wire electrodes.
 AWS A5.9:
Filler wires.
 BS EN ISO 14175:
Shielding gases.
Copyright © TWI Ltd
Welding Consumables
TIG/PAW rods
Welding
fluxes
(SAW)
Cored wire
SAW strips
SAW solid
wire
MIG/MAG
solid wire
Courtesy of ESAB AB
Covered
electrodes
Copyright © TWI Ltd
Copyright © TWI Ltd
Welding Consumable Gases
Welding gases
 GMAW, FCAW, TIG, Oxy-fuel.
 Supplied in cylinders or
storage tanks for large
quantities.
 Colour coded cylinders to
minimise wrong use.
 Subject to regulations
concerned handling,
quantities and positioning of
storage areas.
Copyright © TWI Ltd
15‐1
Welding Consumable Gases
 Moisture content is
limited to avoid cold
cracking.
 Dew point (the
temperature at which
the vapour begins to
condense) must be
checked.
Welding Consumables
Each consumable is critical in respect to
 Size.
 Classification/supplier.
 Condition.
 Treatments eg baking/drying.
 Handling and storage is critical for consumable
control.
 Handling and storage of gases is critical for
safety.
Copyright © TWI Ltd
Copyright © TWI Ltd
Quality Assurance
MMA Covered Electrodes
Copyright © TWI Ltd
Copyright © TWI Ltd
MMA Welding Consumables
The three main electrode covering types used in
MMA welding
 Cellulosic - deep penetration/fusion.
 Rutile - general purpose.
 Basic - low hydrogen.
MMA Welding Consumables
Plastic foil sealed cardboard box
 Rutile electrodes.
 General purpose basic electrodes.
Courtesy of Lincoln Electric
Tin can
 Cellulosic electrodes.
Vacuum sealed pack
 Extra low hydrogen
electrodes.
Copyright © TWI Ltd
Courtesy of Lincoln Electric
Welding consumables
 Filler material must be stored in an area with
controlled temperature and humidity.
 Poor handling and incorrect stacking may damage
coatings, rendering the electrodes unusable.
 There should be an issue and return policy for
welding consumables (system procedure).
 Control systems for electrode treatment must be
checked and calibrated; those operations must be
recorded.
 Filler material suppliers must be approved before
purchasing any material.
Welding Consumables
Copyright © TWI Ltd
15‐2
MMA Welding Consumables
Cellulosic electrodes
 Covering contains cellulose (organic material).
 Produce a gas shield high in hydrogen raising the
arc voltage.
 Deep penetration/fusion characteristics enables
welding at high speed without risk of lack of
fusion.
 Generates high level of fumes and H2 cold
cracking.
 Forms a thin slag layer with coarse weld profile.
 Not require baking or drying (excessive heat will
damage electrode covering).
 Mainly used for stove pipe welding.
 Hydrogen content is 80-90ml/100g of weld metal.
MMA Welding Consumables
Rutile electrodes
 Covering contains TiO2 slag former and arc
stabiliser.
 Easy to strike arc, less spatter, excellent for
positional welding.
 Stable, easy-to-use arc can operate in both DC
and AC.
 Slag easy to detach, smooth profile.
 Reasonably good strength weld metal.
 Used mainly on general purpose work.
 Low pressure pipework, support brackets.
 Electrodes can be dried to lower H2 content but
cannot be baked as it will destroy the coating.
 Hydrogen content is 25-30ml/100g of weld metal.
Copyright © TWI Ltd
Copyright © TWI Ltd
MMA Welding Consumables
High recovery rutile electrodes
Characteristics:
 Coating is bulked out with iron powder.
 Iron powder gives the electrode high recovery.
 Extra weld metal from the iron powder can
mean that weld deposit from a single
electrode can be as high as 180% of the core
wire weight.
 Give good productivity.
 Large weld beads with smooth profile can look
very similar to SAW welds.
MMA Welding Consumables
Basic covering
 Produce convex weld profile and difficult to
detach slag.
 Very suitable for for high pressure work, thick
section steel and for high strength steels.
 Prior to use electrodes should be baked,
typically 350°C for 2 hour plus to reduce
moisture to very low levels and achieve low
hydrogen potential status.
Copyright © TWI Ltd
Copyright © TWI Ltd
BS EN ISO 2560
MMA Covered Electrodes
MMA Welding Consumables
 Contain calcium fluoride and calcium
carbonate compounds.
 Cannot be rebaked indefinitely!
 Low hydrogen potential gives weld metal very
good toughness and YS.
 Have the lowest level of hydrogen (less than
5ml/100g of weld metal).
Compulsory
Optional
Copyright © TWI Ltd
Copyright © TWI Ltd
Copyright © 2004 TWI Ltd
15‐3
MMA Welding Consumables
Covered Electrode Treatment
Types of electrodes (for C, C-Mn steels):
BE EN ISO
2560
AWS A5.1
Cellulosic
E XX X C
EXX10
EXX11
Rutile
E XX X R
EXX12
EXX13
Rutile heavy
coated
E XX X RR
EXX24
E XX X B
EXX15
EXX16
EXX18
Basic
Cellulosic
electrodes
Use straight from the box No baking/drying!
Rutile
electrodes
If necessary, dry up to
120°C - No baking!
Vacuum
packed basic
electrodes
Use straight from the pack
within manufacturers
recommendations
Copyright © TWI Ltd
Covered Electrode Treatment
Note: This is to be done in accordance
with manufacturers recommendations
Basic electrodes
Copyright © TWI Ltd
Covered Electrode Treatment
1: Electrode size (diameter and length).
Baking in oven 2
hours at 350°C!
2: Covering condition: adherence, cracks, chips and
concentricity.
Limited number
of rebakes!
After baking, maintain
in oven at 150°C
3: Electrode designation.
EN 2560-E 50 3 B
If not used within 4
hours, return to oven
and rebake!
Arc ignition enhancing materials (optional!)
Use from quivers
at 75°C
Weld
Copyright © TWI Ltd
Welding Consumables
See BS EN ISO 544 for further information
Copyright © TWI Ltd
TIG Welding Consumables
Welding consumables for TIG
 Filler wires, shielding gases, tungsten
electrodes (non-consumable).
 Filler wires of different materials composition
and variable diameters available in standard
lengths, with applicable code stamped for
identification.
 Steel filler wires of very high quality, with
copper coating to resist corrosion.
 Shielding gases mainly argon and helium,
usually of highest purity (99.9%).
TIG Consumables
Copyright © TWI Ltd
Copyright © TWI Ltd
15‐4
TIG Welding Consumables
Welding rods
 Supplied in cardboard/plastic tubes.
Fusible Inserts
Pre-placed filler material
Before welding
Courtesy of Lincoln Electric
 Must be kept clean and free from oil and dust.
 Might require degreasing.
Copyright © TWI Ltd
Shielding Gases for TIG Welding
Argon
 Low cost and greater availability.
 Heavier than air - lower flow rates than
Helium.
 Low thermal conductivity - wide top bead
profile.
 Low ionisation potential - easier arc starting,
better arc stability with AC, cleaning effect.
 For the same arc current produce less heat
than helium - reduced penetration, wider HAZ.
 To obtain the same arc power, argon requires
a higher current - increased undercut.
Copyright © TWI Ltd
Shielding Gases for TIG Welding
Hydrogen
 Not an inert gas - not used as a primary
shielding gas.
 Increase the heat input - faster travel speed
and increased penetration.
 Better wetting action - improved bead profile.
 Produce a cleaner weld bead surface.
 Added to argon (up to 5%) - only for
austenitic stainless steels and nickel alloys.
 Flammable and explosive.
Copyright © TWI Ltd
After welding
Other terms used include
 EB inserts (electric boat
company).
 Consumable socket rings
(CSR).
Copyright © TWI Ltd
Shielding Gases for TIG Welding
Helium
 Costly and lower availability than Argon.
 Lighter than air - requires a higher flow rate
compared with argon (2-3 times).
 Higher ionisation potential - poor arc stability
with AC, less forgiving for manual welding.
 For the same arc current produce more heat
than argon - increased penetration, welding of
metals with high melting point or thermal
conductivity.
 To obtain the same arc power, helium requires
a lower current - no undercut.
Copyright © TWI Ltd
Shielding Gases for TIG Welding
Nitrogen
 Not an inert gas.
 High availability – cheap.
 Added to argon (up to 5%) - only for back
purge for duplex stainless, austenitic stainless
steels and copper alloys.
 Not used for mild steels (age embrittlement).
 Strictly prohibited in case of Ni and Ni alloys
(porosity).
Copyright © TWI Ltd
15‐5
Welding Consumables
MIG/MAG Welding Consumables
Welding consumables for MIG/MAG
 Spools of continuous electrode wires and
shielding gases.
 Variable spool size (1-15Kg) and wire
diameter (0.6-1.6mm) supplied in random or
orderly layers.
 Basic selection of different materials and their
alloys as electrode wires.
 Some steel electrode wires copper coating
purpose is corrosion resistance and electrical
pick-up.
 Gases can be pure CO2, CO2+argon mixes and
argon+2%O2 mixes (stainless steels).
MIG/MAG Consumables
Copyright © TWI Ltd
Copyright © TWI Ltd
MIG/MAG Welding Consumables
MIG/MAG Welding Consumables
Welding wires
Welding wires
 Supplied on wire/plastic spools or coils.
 Random or line winding.
 Carbon and low alloy wires may be copper coated.
 Stainless steel wires are not coated.
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
Plastic spool
Wire spool
Courtesy of Lincoln Electric
Coil
Courtesy of ESAB AB
 Wires must be kept clean and free from oil and dust.
 Flux cored wires does not require baking or drying.
Copyright © TWI Ltd
Copyright © TWI Ltd
MIG/MAG Welding Consumables
How to check the quality of welding wires
MIG/MAG Shielding Gases
Ar
Ar-He
He
CO2
Cast diameter
Helix size - limited to 25mm to
avoid problems with arc
wandering!
Cast diameter improves the contact force and defines the contact point;
usually 400-1200mm.
Contact point close to
contact tip end - good!
Contact point remote from
contact tip end - poor!
Copyright © TWI Ltd
Argon (Ar)
 Higher density than air; low thermal conductivity - the
arc has a high energy inner cone; good wetting at the
toes; low ionisation potential.
Helium (He)
 Lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high
ionisation potential.
Carbon dioxide (CO2)
 Cheap; deep penetration profile; cannot support spray
transfer; poor wetting; high spatter.
Copyright © TWI Ltd
15‐6
MIG/MAG Shielding Gases
Gases for dip transfer
 CO2: Carbon steels only; deep penetration;
fast welding speed; high spatter levels.
 Ar + up to 25% CO2: Carbon and low alloy
steels; minimum spatter; good wetting and
bead contour.
 90% He + 7,5% Ar + 2,5% CO2: Stainless
steels; minimises undercut; small HAZ.
 Ar: Al, Mg, Cu, Ni and their alloys on thin
sections.
 Ar + He mixtures: Al, Mg, Cu, Ni and their
alloys on thicker sections (over 3mm).
MIG/MAG Shielding Gases
Gases for spray transfer
 Ar + (5-18)% CO2: Carbon steels; minimum
spatter; good wetting and bead contour.
 Ar + 2% O2: Low alloy steels; minimise
undercut; provides good toughness.
 Ar + 2% O2 or CO2: Stainless steels;
improved arc stability; provides good fusion.
 Ar: Al, Mg, Cu, Ni, Ti and their alloys.
 Ar + He mixtures: Al, Cu, Ni and their alloys;
hotter arc than pure Ar to offset heat
dissipation.
 Ar + (25-30)% N2: Cu alloys; greater heat
input.
Copyright © TWI Ltd
Copyright © TWI Ltd
Welding Consumables
Flux Core Wire Consumables
Flux Core Wire Consumables
Functions of metallic
sheath
 Provide form stability
to the wire.
 Serves as current
transfer during
welding.
Function of the
filling powder
 Stabilise the arc.
 Add alloy elements.
 Produce gaseous
shield.
 Produce slag.
 Add iron powder.
Copyright © TWI Ltd
Copyright © TWI Ltd
Types of Cored Wire
Seamless
cored wire
Butt joint
cored wire
Types of Cored Wire
Seamless
cored wire
Overlapping
cored wire
 Not sensitive to moisture pick-up.
 Can be copper coated - better current
transfer.
 Thick sheath - good form stability - 2 roll drive
feeding possible.
 Difficult to manufacture.
Copyright © TWI Ltd




Butt joint
cored wire
Overlapping
cored wire
Good resistance to moisture pick-up.
Can be copper coated.
Thick sheath.
Difficult to seal the sheath.
Copyright © TWI Ltd
15‐7
Types of Cored Wire
Seamless
cored wire




Butt joint
cored wire
Overlapping
cored wire
Welding Consumables
SAW Consumables
Sensitive to moisture pick-up.
Cannot be copper coated.
Thin sheath.
Easy to manufacture.
Copyright © TWI Ltd
Copyright © TWI Ltd
SAW Filler Material
Welding wires
 Supplied on coils, reels or drums.
 Random or line winding.
Courtesy of Lincoln Electric
SAW Filler Material
Welding wires can be used to weld
 Carbon steels.
 Low alloy steels.
 Creep resisting steels.
 Stainless steels.
 Nickel-base alloys.
 Special alloys for surfacing applications.
Courtesy of ESAB AB
Courtesy of Lincoln Electric
Coil
Reel
Drum
(approximately 25kg)
(approximately 300kg)
(approximately 450kg)
Copyright © TWI Ltd
SAW Filler Material
Welding wires
 Carbon and low alloy wires are copper coated.
 Stainless steel wires are not coated.
Welding wires can be
 Solid wires.
 Metal-cored wires.
Copyright © TWI Ltd
SAW Filler Material
Copper coating functions
 To assure a good electric contact between wire
and contact tip.
 To assure a smooth feed of the wire through
the guide tube, feed rolls and contact tip
(decrease contact tube wear).
 To provide protection against corrosion.
 Wires must be kept clean and free from oil and dust.
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
Copyright © TWI Ltd
Copyright © TWI Ltd
15‐8
SAW Consumables
Welding fluxes
 Are granular mineral compounds mixed
according to various formulations.
 Shield the molten weld pool from the
atmosphere.
 Clean the molten weld pool.
 Can modify the chemical composition of the weld
metal.
 Prevents rapid escape of heat from welding zone.
 Influence the shape of the weld bead (wetting
action).
 Can be fused, agglomerated or mixed.
 Must be kept warm and dry to avoid porosity.
SAW Consumables
Welding flux
 Supplied in bags/pails (approximately 25kg) or
bulk bags (approximately 1200kg).
 Might be fused, agglomerated or mixed.
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
Copyright © TWI Ltd
Copyright © TWI Ltd
SAW Consumables
SA welding flux:
 Must be kept warm and dry.
 Handling and stacking requires care.
Fused fluxes:
 Are normally not hygroscopic but particles can hold
surface moisture.
 Only drying.
Agglomerated fluxes:
 Contain chemically bonded water.
 Similar treatment as basic electrodes.
 For high quality, agglomerated fluxes can be
recycled with new flux added.
 If flux is too fine it will pack and not feed properly.
 Cannot be recycled indefinitely.
Courtesy of Lincoln Electric
Ceramic Backing
Ceramic backing
 Used to support the
weld pool on root
runs.
 Usually fitted on an
aluminium self
adhesive tape.
 Allow increased welding current without danger
of burn-through - increased productivity,
consistent quality.
 Different profiles to suit different applications.
 No backing/drying required.
Copyright © TWI Ltd
Copyright © TWI Ltd
CSWIP 3.2 Senior Welding Inspector
Inspection of Consumables
Why?
 To assess whether the products are in
compliance with the requirements of the order
or not - see BS EN 10204.
How?
 Non-specific inspection:
Welding Consumables
Inspection and Validation


Copyright © TWI Ltd
Carried out by the manufacturer in accordance
with its own procedures.
The products inspected are not necessarily the
products supplied!
Copyright © TWI Ltd
15‐9
Inspection of Consumables
Specific inspection
 Carried out before delivery in accordance to
product specification.
 Inspection is performed on the products to be
supplied or on test units of which the products
supplied are part.
BS EN 10204-Type of Documents
Type 2.1
Non-specific
inspection
documents
 Name:
− Declaration of compliance
with the order.
 Content:
− Statement of compliance
with the order (doesn’t
include test results!)
 Who validate it:
− The manufacturer.
 Name:
‒ Test report.
 Content:
‒ Statement of compliance
with the order (include
test results!)
 Who validate it:
‒ The manufacturer.
Copyright © TWI Ltd
BS EN 10204-Type of Documents
Type 3.1
Specific
inspection
documents
 Name:
− Inspection certificate 3.1.
 Content:
− Statement of compliance
with the order (include
specific test results!)
 Who validate it ?
− The manufacturer
inspection (independent
of manufacturing
department!)
Type 2.2
Copyright © TWI Ltd
Welding Consumables
Type 3.2
 Name:
− Inspection certificate 3.2.
 Content:
− Statement of compliance with
the order (include specific test
results!)
 Who validate it?
− The manufacturer inspection
(independent of manufacturing
department!) + purchaser’s/
official designated authorised
inspector.
Copyright © TWI Ltd
Welding Consumables
You are currently employed as a Senior Welding
Inspector in a fabrication yard.
The yard has numerous major oil and gas
projects under construction.
Part of your duties is to monitor the control,
storage and handling of welding consumables
used during the construction.
Copyright © TWI Ltd
Any Questions
?
Copyright © TWI Ltd
Question 1
One of your inspectors informs you that a batch of E8018
electrodes has arrived on site and requires a heat treatment
before use. Which of the following best applies to this type
of electrode?
a. Generally this type of electrode can be used directly
from the container with no heat treatments required
b. In accordance with the TWI Specification, these types of
electrodes are not permitted for use on this type of
fabrication
c. This type of electrode can be used providing the
electrodes flux has been recycled to a maximum of
50:50 ratios old to new
d. All options are incorrect
Copyright © TWI Ltd
15‐10
Question 2
Question 3
During welding one of your inspectors informs you that the
fabricators are recycling SAW welding flux 30% new to
70% old. Is this permitted in accordance with the TWI
Specification?
You are informed that the approved supplier of electrodes
cannot make a delivery for two weeks. He asks if another
manufacturer can be used, the electrodes are the same
specification and size.
a. This would not be permitted as the TWI specification
states a ratio of 50:50 shall be applied
b. SAW fluxes can’t be recycled under any conditions
c. This would be permitted as it’s in accordance with the
TWI Specifications
d. This decision would generally be up to the welding
supervisor
a. No, the electrodes must be from the original
manufacturer (Table 7)
b. Yes, the electrodes can be used as they are the same
specification.
c. It depends on whether the client will accept the change
d. They can be accepted once an all weld tensile test is
completed.
Copyright © TWI Ltd
Question 4
Copyright © TWI Ltd
Question 5
A large batch of MAG wires has arrived on site, one of your
inspectors informs you that the copper coating on some of
the wire spools has been damaged during transportation.
What is the purpose of the copper coating?
A batch of E46 3 1Ni B electrodes has arrived on site. One
of your inspectors asks the question "what is the minimum
yield value of these electrodes". Which of the following is
correct?
a. The copper is added to the wire to aid fusion and
improve mechanical properties of the deposited weld
metal.
b. The copper aides electrical pick up and protects the
wire from corrosion
c. The copper coating promotes weld metal fluidity and
improves positional welding
d. All options are incorrect
a. In accordance with AWS A5.1 the minimum UTS value
would be 460 N/mm2
b. In accordance with BS EN ISO 2560 the minimum UTS
value would be 720 N/mm2
c. In accordance with BS EN ISO 2560 the minimum yield
value would be 460 N/mm2
d. In accordance with BS EN ISO 2560 the minimum yield
value would be 500 N/mm2
Copyright © TWI Ltd
Question 6
You notice a batch of cellulosic electrodes in the welding
consumable store, which of the following statements is
correct for this type of electrode?
a. These electrodes can be used to control hydrogen
levels to below 15ml per 100 grams of weld metal
b. These electrodes should be baked prior to use
c. These type of electrodes are especially suited to the PG
welding position
d. 2 Options are correct
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 7
During your morning inspection of the welding stores, you
notice that certain electrodes are being baked in their
original container in correctly controlled baking ovens. In
accordance with the TWI Specification is this a correct
practice?
a. Yes, providing the treatment is in accordance with the
manufacturers instructions
b. No, under no circumstances should electrodes be
baked
c. Yes providing after baking the electrodes are stored in
such a way as to keep them free from moisture intake
d. No, not permitted
Copyright © TWI Ltd
15‐11
Question 8
A Q&T section is being welded with rutile electrodes. It has
been proved that Hydrogen cracking does not occur in this
type of parent material. Which of the following statements
are true?
a. If HICC is not a problem in the parent material, rutile
electrodes can be used.
b. Basic electrodes must be used as the cracking occurs in
the weld metal
c. If the rutile electrodes are baked before use, the
hydrogen level should not be a problem
d. Any process that produces less than 20ml of hydrogen
per 100 grams of weld metal should stop any HICC
occurring.
Copyright © TWI Ltd
Question 9
One of your inspectors is unsure of the toughness value of
an electrode classified as E50 3 2Ni B, which of the
following is the correct answer?
a.
b.
c.
d.
Maximum toughness 47J
Minimum toughness 50J
Minimum toughness 47J
Maximum toughness 50J
at -30°C
at -20°C
at -30°C
at -20°C
Copyright © TWI Ltd
Question 10
Tungsten electrodes are considered consumables. Therefore,
it is crucial that they are used correctly. Which of the
following statements is correct concerning Tungsten
electrodes?
a. Zirconiated electrodes are used on DC negative as they
concentrate the arc
b. Zirconiated electrodes are used on AC as they can
withstand more heat on the positive cycle
c. Zirconiated electrodes are multi purpose for use on DC
and AC
d. Zirconiated electrodes are designed to be used with a
long taper preparation.
Copyright © TWI Ltd
15‐12
Se ct ion 1 6
M AG W e ldin g
16
M AG W e ldin g
1 6 .1
The pr oce ss
Known in t he USA as gas m et al arc welding ( GMAW) . The MI G/ MAG welding
process is a ver sat ile t echnique suit able for bot h t hin sheet and t hick sect ion
com ponent s in m ost m et allic m at erials.
I n t he process, an arc is st ruck bet w een t he end of a wir e elect r ode and t he
wor kpiece, m elt ing bot h t o form a w eld pool. The wire ser ves as t he sour ce of
heat ( via t he ar c at t he wire t ip) and filler m et al for t he j oint .
The wire is fed t hrough a copper cont act t ube ( also called a cont act t ip) which
conduct s welding current int o t he wire. The weld pool is prot ect ed from t he
surr ounding at m ospher e by a shielding gas fed t hrough a nozzle surrounding
t he wire.
Shielding gas select ion depends on t he m at erial being welded and t he
applicat ion. The wire is fed from a reel by a m ot or drive and t he w elder or
m achine m oves t he w elding gun or t orch along t he j oint line.
The process offers high pr oduct ivit y and is econom ical because t he consum able
wire is cont inuously fed. A diagram of t he process is shown in Figure 16.1.
The MI G/ MAG pr ocess uses sem iaut om at ic, m echanised, or aut om at ic
equipm ent . I n sem iaut om at ic welding, t he wire feed rat e and arc lengt h are
cont r olled aut om at ically, but t he t ravel speed and wire posit ion are under
m anual cont rol.
I n m echanised welding, all param et er s ar e under aut om at ic cont r ol, but t hey
can be varied m anually during welding, eg st eering of t he w elding head and
adj ust m ent of wire feed speed and arc volt age.
Wit h aut om at ic equipm ent , t her e is no m anual int ervent ion during welding.
Figure 16.2 show s equipm ent r equired for t he MI G/ MAG pr ocess.
Figur e 1 6 .1 M I G/ M AG w e lding.
WI S10- 30816
MAG Welding
16-1
Copyright © TWI Lt d
Figur e 1 6 .2 M I G/ M AG w e lding e quipm e n t .
Adv a nt a ge s of t he M I G/ M AG pr oce ss











Cont inuous wire feed.
Aut om at ic self- regulat ion of t he ar c lengt h.
High deposit ion rat e and m inim al num ber of st op/ st art locat ions.
High consum able efficiency.
Heat input s in t he range 0.1- 2.0kJ/ m m .
Low hydr ogen pot ent ial process.
Welder has good visibilit y of w eld pool and j oint line.
Lit t le or no post w eld cleaning.
Can be used in all posit ions ( dip t ransfer) .
Good pr ocess cont r ol possibilit ies.
Wide range of applicat ion.
D isa dv a nt a ge s









WI S10- 30816
MAG Welding
No independent cont r ol of filler addit ion.
Difficult t o set up opt im um param et er s t o m inim ise spat t er levels.
Risk of lack of fusion when using dip t ransfer on t hicker w eldm ent s.
High level of equipm ent m aint enance.
Low er heat input can lead t o high hardness values.
Higher equipm ent cost t han MMA ( m anual m et al arc) welding.
Sit e welding requires special precaut ions t o exclude draught s which m ay
dist urb t he gas shield.
Joint and part access is not as good as MMA or TI G welding.
Cleanliness of base m et al slag processes can t olerat e great er cont am inat ion.
16-2
Copyright © TWI Lt d
1 6 .2
Pr oce ss va r ia ble s
The prim ary variables in MI G/ MAG w elding are:









1 6 .2 .1
Welding curr ent / wire feed speed.
Volt age.
Gases.
Trav el speed and elect r ode orient at ion.
I nduct ance.
Cont act t ip t o work dist ance.
Nozzle t o w or k dist ance.
Shielding gas nozzle.
Type of m et al t ransfer.
W e ldin g cu r r e n t / w ir e fe e d spe e d
On MI G/ MAG w elding set s t here is no cont r ol t o set t he welding current . The
elect rical charact erist ics of t he welding set ( flat or const ant v olt age t ype)
aut om at ically alt ers t he welding current wit h changes t o t he set wire feed speed
t o achieve a const ant ar c lengt h.
I ncreasing t he wire feed, and t her efor e curr ent , increases wire burn- off,
deposit ion rat e and penet rat ion.
Curr ent t ype is alm ost always DC+ v e, alt hough som e cor ed wires require DC- v e
for best r esult s.
1 6 .2 .2
Volt a ge
This is set t o achieve st eady sm oot h welding condit ions and is generally
increased as t he wire feed speed is increased.
I ncrease in volt age increases t he widt h of t he weld and reduces penet rat ion.
1 6 .2 .3
Tr a ve l spe e d a nd e le ct r ode or ie nt a t ion
The fast er t he t ravel speed t he less penet rat ion, narr ow er bead widt h and t he
higher risk of undercut


I ncreasing t ravel speed
Reduced penet rat ion and widt h, undercut
Figur e 1 6 .3 The e ffe ct of t r a ve l spe e d.
WI S10- 30816
MAG Welding
16-3
Copyright © TWI Lt d
Penet rat ion
Excess weld m et al
Undercut
Deep
Moderat e
Maxim um Moderat e
Severe
Moderat e
Shallow
Minim um
Minim um
Figur e 1 6 .4 The e ffe ct of t or ch a ngle .
1 6 .2 .4
Effe ct of cont a ct t ip t o w or k pie ce dist a nce ( CTW D )
The CTWD has an influence over t he w elding curr ent because of resist ive
heat ing in t he elect r ode ext ension ( see Figure 16.4) . The welding cur rent
required t o m elt t he elect r ode at t he required rat e ( t o m at ch t he wire feed
speed) reduces as t he CTWD is increased. Long elect rode ext ensions can cause
lack of penet rat ion, for exam ple, in narr ow gap j oint s, or w it h poor
m anipulat ion of t he welding gun. Conversely, t he welding current increases
when t he CTWD is reduced.
Cont act t ip
Gas nozzle
Cont act t ip
set back
Nozzle- t o- wor k
( st and- off)
dist ance
Elect r ode
ext ension
Arc le n gt h
Cont act t ipt o- work
dist ance
Workpiece
Figur e 1 6 .5 Cont a ct t ip t o w or k pie ce dist a nce ; e le ct r ode e x t e nsion a n d noz zle
t o w or k pie ce dist a nce .
WI S10- 30816
MAG Welding
16-4
Copyright © TWI Lt d
I ncreased ext ension
Figur e 1 6 .6 The e ffe ct of incr e a sing e le ct r ode e x t e nsion.
The elect r ode ext ension should be check ed when set t ing- up welding condit ions
or when fit t ing a new cont act t ube. Nor m ally m easur ed from t he cont act t ube t o
t he wor k piece ( Figure 16.5) suggest ed CTWDs for t he principal m et al t ransfer
m odes are:
1 6 .2 .5
M e t a l t r a n sfe r m ode
CTW D , m m
Dip
Spray
Pulse
10- 15
20- 25
15- 20
Effe ct of n oz z le t o w or k dist a nce
Nozzle t o w or k dist ance ( see Figure 16.4) has a considerable effect on gas
shielding efficiency; a decrease having t he effect of st iffening t he colum n. The
nozzle t o work dist ance is t ypically 12- 15m m . I f t he CTWD is sim ult aneously
reduced, how ev er, t he deposit ion rat e at a given current is decr eased and
visibilit y and accessibilit y are affect ed; so, in pract ice, a com prom ise is
necessary . The following gives suggest ed set t ings for t he m ode of m et al
t ransfer being used
1 6 .2 .6
M e t a l t r a n sfe r m ode
Cont a ct t ip posit ion r e la t ive t o noz z le
Dip
Spray
Spray ( alum inium )
2m m inside t o 2m m prot ruding
4- 8m m inside
6- 10m m inside
Shie lding ga s noz z le
The purpose of t he shielding gas nozzle is t o produce a lam inar gas flow in
order t o prot ect t he w eld pool fr om at m ospheric cont am inat ion. Nozzle sizes
range from 13- 22m m diam et er. The nozzle diam et er should be increased in
relat ion t o t he size of t he w eld pool.
WI S10- 30816
MAG Welding
16-5
Copyright © TWI Lt d
1 6 .2 .7
Type s of m e t a l t r a n sf e r
Figur e 1 6 .7 Ar c cha r a ct e r ist ic cur ve .
1
D ip t r a nsf e r :
Ke y cha r a ct e r ist ics:







Met al t ransfer by wire dipping or short circuit ing int o t he weld pool.
Relat ively low heat input process.
Low weld pool fluidit y.
Used for t hin sheet m et al above 0.8 and t ypically less t han 3.2m m ,
posit ional welding of t hicker sect ion and root runs in open but t j oint s.
Process st abilit y and spat t er can be a pr oblem if poorly t uned.
Lack of fusion risk if poorly set up and applied.
Not used for non- fer rous m et als and alloys.
I n dip t ransfer t he wire short - circuit s t he arc bet ween 50–200 t im es/ sec. This
t ype of t ransfer is norm ally achieved wit h CO 2 or m ixt ures of CO 2 and argon gas
+ low am ps and w elding volt s < 24V.
Figur e 1 6 .8 D ip t r a nsfe r .
WI S10- 30816
MAG Welding
16-6
Copyright © TWI Lt d
2
Spr a y t r a nsf e r :
Ke y cha r a ct e r ist ics:





Free- flight m et al t ransfer.
High heat input .
High deposit ion rat e.
Sm oot h, st able arc.
Used on st eels above 6m m t hickness and alum inium alloys abov e 3m m
t hickness.
Spray t ransfer occur s at high current s and high volt ages. Abov e t he t ransit ion
curr ent , m et al t ransfer is in t he form of a fine spray of sm all droplet s, which are
proj ect ed across t he arc wit h low spat t er levels. The high welding cur rent
produces st rong elect rom agnet ic forces ( know n as t he pinch effect ' t hat cause
t he m olt en filam ent support ing t he dr oplet t o neck down. The droplet s det ach
from t he t ip of t he wire and accelerat e across t he arc gap.
Wit h st eels it can be used only in down- hand but t s and H/ V fillet welds, but
gives significant ly higher deposit ion rat e, penet rat ion and fusion t han t he dip
t ransfer m ode. Wit h alum inum alloys it can be used in all posit ions.
3
Pulse d t r a nsfe r :
Ke y cha r a ct e r ist ics:








WI S10- 30816
MAG Welding
Free- flight droplet t ransfer wit hout short - circuit ing over t he ent ire w orking
range.
Ver y low spat t er.
Low er heat input t han spray t ransfer .
Reduced risk of lack of fusion com par ed wit h dip t ransfer .
Cont rol of w eld bead pr ofile for dynam ically loaded part s.
Process cont rol/ flexibilit y.
Enables use of larger diam et er, less expensive wires wit h t hinner plat es –
m or e.
Easily fed ( a part icular advant age for alum inium welding) .
16-7
Copyright © TWI Lt d
Pulsing t he welding current ext ends t he range of spray t ransfer oper at ion well
below t he nat ural t ransit ion from dip t o spray t ransfer. This allows sm oot h,
spat t er- fr ee spray t ransfer t o be obt ained at m ean cur rent s below t he t ransit ion
level, eg 50- 150A and at lower heat input s.
A t ypical pulse waveform and t he m ain pulse welding variables are show n
in Figure 16.10. Pulse t ransfer uses pulses of curr ent t o fire a single globule of
m et al acr oss t he arc gap at a fr equency bet ween 50–300 pulses/ sec. Pulse
t ransfer is a dev elopm ent of spray t ransfer t hat gives posit ional welding
capabilit y for st eels, com bined wit h cont rolled heat input , good fusion, and high
product ivit y. I t m ay be used for all sheet st eel t hickness > 1m m , but is m ainly
used for posit ional welding of st eels > 6m m .
Figur e 1 6 .1 0 Pulse d w e lding w a ve for m a nd pa r a m e t e r s.
4
Globula r t r a n sfe r :
Ke y cha r a ct e r ist ics:






I rr egular m et al t ransfer .
Medium heat input .
Medium deposit ion rat e.
Risk of spat t er .
Not widely used in t he UK; can be used for m echanised welding of m edium .
Thickness st eels ( t ypically 3- 6m m ) in t he flat ( PA) posit ion.
The globular t ransfer range occupies t he t r ansit ional range of ar c v olt age
bet ween fr ee flight and fully short - circuit ing t ransfer. I rr egular droplet t ransfer
and arc inst abilit y are inherent , part icularly when operat ing near t he t ransit ion
t hreshold. I n globular t ransfer , a m olt en dr oplet of sev eral t im es t he elect r ode
diam et er form s on t he wire t ip. Gravit y ev ent ually det aches t he globule when
it s weight over com es surface t ension forces and t ransfer t ak es place oft en wit h
excessive spat t er
To m inim ise spat t er levels, it is com m on t o operat e wit h a very short arc lengt h
and in som e cases a buried arc t echnique is adopt ed. Globular t ransfer can only
be used in t he flat posit ion and is oft en associat ed wit h lack of penet rat ion,
fusion defect s and uneven weld beads, because of t he irregular t ransfer and
t endency for arc wander .
WI S10- 30816
MAG Welding
16-8
Copyright © TWI Lt d
1 6 .2 .8
I nduct a nce
W ha t doe s induct a nce do?
When MI G w elding in t he dip t ransfer m ode, t he welding elect rode t ouches t he
weld pool, causing a short circuit . During t he short circuit , t he arc volt age is
nearly zer o. I f t he const ant volt age power supply responded inst ant ly, ver y high
curr ent w ould im m ediat ely begin t o flow t hrough t he weldingcircuit . The rapid
rise in current t o a high value would m elt t he short - circuit ed elect rode fr ee wit h
explosive for ce, dispelling t he weld m et al and causing considerable spat t er.
I nduct ance is t he propert y in an elect rical circuit t hat slows down t he rat e of
curr ent rise ( Figure 16.11) . The curr ent t rav elling t hrough an induct ance coil
cr eat es a m agnet ic field. This m agnet ic field cr eat es a curr ent in t he w elding
circuit t hat is in opposit ion t o t he welding current . I ncr easing t he induct ance will
also increase t he arc t im e and decrease t he fr equency of short - circuit ing.
For each elect rode feed rat e, t her e is an opt im um value of induct ance. Too lit t le
induct ance result s in excessive spat t er. I f t oo m uch induct ance is used, t he
curr ent will not rise fast enough and t he m olt en t ip of t he elect rode is not
heat ed sufficient ly causing t he elect r ode t o st ub int o t he base m et al. Modern
elect r onic power sour ces aut om at ically set t he induct ance t o give a sm oot h ar c
and m et al t ransfer.
Figur e 1 6 .1 1 Re la t ion sh ip be t w e e n induct a nce a nd cur r e nt r ise .
1 6 .3
W e lding con sum a ble s
1 6 .3 .1
Solid w ir e s
Usually m ade in sizes from 0.6 t o 1,6m m diam et er t hey ar e pr oduced wit h an
analysis which essent ially m at ches t he m at erials being j oined. Addit ional
elem ent s ar e oft en added especially ext ra de- oxidant s in st eel wires. C- Mn and
low alloy st eel wires are usually copper coat ed t o reduce t he risk of rust ing and
prom ot e bet t er elect rical cont act .
WI S10- 30816
MAG Welding
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Copyright © TWI Lt d
1 6 .3 .2
Flux cor e d w ir e s
A cored wire consist s of a m et al sheat h cont aining a granular flux. This flux can
cont ain elem ent s t hat would norm ally be used in MMA elect rodes and so t he
process has a v ery wide range of applicat ions.
I n addit ion we can also add gas producing elem ent s and com pounds t o t he flux
and so t he process can becom e independent of a separat e gas shield, which
rest rict ed t he use of convent ional MI G/ MAG w elding in m any field applicat ions.
Most wires ar e sealed m echanically and herm et ically wit h various form s of j oint .
The effect iveness of t he j oint of t he wire is an inspect ion point of cor ed wire
welding as m oist ure can easily be absorbed int o a dam aged or poor seam .
Wire t ypes com m only used ar e:




Rut ile – which give good posit ional capabilit ies..
Basic – also posit ional but good on “ dirt y” m at erial.
Met al cored – higher product ivit y and som e having excellent root run
capabilit ies.
Self- shielded – no ext er nal gas needed.
Baking of cored wires is ineffect ive and will do not hing t o rest or e t he condit ion
of a cont am inat ed flux wit hin a wire.
N ot e : Unlike MMA elect rodes t he pot ent ial hydrogen levels and m echanical
propert ies of welds wit h rut ile wires can equal t hose of t he basic t ypes.
1 6 .4
I m por t a nt inspe ct ion point s/ che ck s w he n M I G/ M AG w e lding
1
The w e lding e qu ipm e nt
A visual check should be m ade t o ensur e t he welding equipm ent is in good
condit ion.
2
The e le ct r ode w ir e
The diam et er, specificat ion and t he qualit y of t he wire are t he m ain
inspect ion headings. The level of de- oxidat ion of t he wire is an im port ant
fact or wit h single, double and t riple de- oxidised wires being available.
The higher t he level of de- oxidant s in t he wire, t hen t he lower t he chance of
por osit y in t he weld. The qualit y of t he wire winding, copper coat ing, and
t em per are also im port ant fact ors in m inim ising wire feed problem s.
Qua lit y of w ir e w in dings a nd incr e a sing cost s
( a) Ra n dom w ound. ( b) La ye r w ound. ( c) Pr e cision la ye r w ou nd.
3
The dr iv e r olls a nd lin e r .
Check t he drive rolls are of t he cor r ect size for t he wire and t hat t he
pressur e is only hand t ight , or j ust sufficient t o drive t he wire. Any ex cess
pressur e will deform t he wire t o an ovular shape. This will m ake t he wire
very difficult t o drive t hrough t he liner and result in arcing in t he cont act t ip
and excessive w ear of t he cont act t ip and liner.
Check t hat t he liner is t he cor rect t ype and size for t he wir e. A size of liner
will generally fit 2 sizes of wire ie ( 0.6 and 0.8) ( 1.0 and 1.2) ( 1.4 and 1.6)
m m diam et er. St eel liner s ar e used for st eel wires and Teflon liners for
alum inium wires.
WI S10- 30816
MAG Welding
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Copyright © TWI Lt d
4
The cont a ct t ip
Check t hat t he cont act t ip is t he cor rect size for t he wire being driven, and
check t he am ount of w ear fr equent ly. Any loss of cont act bet w een t he wire
and cont act t ip will reduce t he efficiency of curr ent pick. Most st eel wires
are copper- coat ed t o m axim ise t he t ransfer of curr ent by cont act bet w een 2
copper sur faces at t he cont act t ip, t his also inhibit s corr osion. The cont act
t ip should be r eplaced r egularly.
5
The conne ct ion s
The lengt h of t he elect ric arc in MI G/ MAG w elding is cont r olled by t he
volt age set t ings. This is achieved by using a const ant v olt age volt / am p
charact erist ic inside t he equipm ent . Any poor connect ion in t he welding
circuit will affect t he nat ure and st abilit y of t he elect ric arc, and is t hus is a
m aj or inspect ion point .
6
Ga s a n d ga s f low r a t e
The t ype of gas used is ext r em ely im port ant t o MI G/ MAG welding, as is t he
flow rat e from t he cylinder, which m ust be adequat e t o give good cov erage
ov er t he solidifying and m olt en m et al t o avoid oxidat ion and porosit y.
7
Ot he r va r ia ble w e ldin g pa r a m e t e r s
Check s should be m ade for cor r ect wire feed speed, volt age, speed of
t ravel, and all ot her essent ial variables of t he pr ocess given on t he
approv ed w elding procedure.
8
Sa fe t y ch e ck s
Check s should be m ade on t he cur rent carr ying capacit y, or dut y cy cle of
equipm ent and elect rical insulat ion. Corr ect ext ract ion syst em s should be in
use t o av oid exposur e t o ozone and fum es.
A check should always be m ade t o ensure t hat t he welder is qualified t o w eld
t he pr ocedur e being em ployed.
Typica l w e lding im pe r fe ct ion s:
1
2
3
4
WI S10- 30816
MAG Welding
Silica inclusion s, ( on ferrit ic st eels only) caused by poor int er- run
cleaning.
La ck of side w a ll f usion during dip t ransfer w elding t hick sect ion vert ically
down.
Por osit y caused from loss of gas shield and low t olerance t o cont am inant s.
Bur n - t hr ough from using t he incorr ect m et al t ransfer m ode on sheet
m et al.
16-11
Copyright © TWI Lt d
Se ct ion 1 7
M M A W e ldin g
17
M M A W e ldin g
1 7 .1
M a nu a l m e t a l a r c/ shie lde d m e t a l a r c w e lding ( M M A/ SM AW )
The m ost v er sat ile of t he welding processes, m anual m et al arc ( MMA) welding is
suit able for w elding m ost fer rous and non- ferr ous m et als, over a wide range of
t hicknesses. The MMA welding process can be used in all posit ions, wit h
reasonable ease of use and relat ively econom ically. The final weld qualit y is
prim arily dependent on t he skill of t he w elder.
When an ar c is st ruck bet ween t he coat ed elect rode and t he workpiece, bot h
t he elect r ode and wor kpiece surface m elt t o for m a w eld pool. The av erage
t em perat ur e of t he arc is approxim at ely 6000°C, whi ch is sufficient t o
sim ult aneously m elt t he par ent m et al, consum able core wire and t he flux
coat ing. The flux form s gas and slag, which prot ect s t he w eld pool from oxygen
and nit rogen in t he surr ounding at m osphere. The m olt en slag solidifies and
cools and m ust be chipped off t he weld bead once t he weld run is com plet e ( or
befor e t he next w eld pass is deposit ed) . The process allows only short lengt hs
of weld t o be pr oduced before a new elect r ode needs t o be insert ed in t he
holder.
Figur e 1 7 .1 The m a nua l m e t a l a r c w e lding pr oce ss.
WI S10- 30816
MMA Welding
17-1
Copyright © TWI Lt d
1 7 .2
M M A w e lding ba sic e quipm e nt r e qu ir e m e n t s
10
1
9
2
3
8
4
7
5
6
1
2
3
4
5
6
7
8
9
10
Pow e r sou r ce t r a nsfor m e r / r e ct if ie r ( const ant curr ent t ype) .
H olding ove n ( holds at t em perat ur es up t o 150°C) .
I nve r t e r pow e r sou r ce ( m ore com pact and port able) .
Ele ct r ode holde r ( of a suit able am perage rat ing) .
Pow e r ca ble ( of a suit able am perage r at ing) .
W e lding visor ( wit h corr ect rat ing for t he am perage/ pr ocess) .
Pow e r r e t u r n ca ble ( of a suit able am perage r at ing) .
Ele ct r ode s ( of a suit able t ype and am perage rat ing) .
Ele ct r ode ove n ( bakes elect r odes at up t o 350°C) .
Cont r ol pa ne l ( on\ off/ am perage/ polarit y/ OCV) .
Figur e 1 7 .2 M M A w e ldin g ba sic e quipm e nt .
1 7 .3
Pow e r r e quir e m e nt s
Manual m et al arc welding can be carried out using eit her direct ( DC) or
alt ernat ing ( AC) curr ent . Wit h DC welding curr ent eit her posit ive ( + ve) or
negat ive ( - ve) polarit y can be used, so cur rent is flowing in one direct ion. AC
welding current flows fr om negat ive t o posit ive and is t wo direct ional.
Pow er sources for MMA welding are t ransform er s ( which t ransform s m ains AC
t o AC suit able for w elding) , t ransform er- r ect ifier s ( which rect ifies AC t o DC) ,
diesel or pet rol driven generat ors ( pr efer red for sit e work) or invert er s ( a m ore
recent addit ion t o welding power sour ces) . For MMA w elding a power source
wit h a const ant cur rent ( drooping) out put charact erist ic m ust be used.
WI S10- 30816
MMA Welding
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Copyright © TWI Lt d
The power source m ust provide:





1 7 .4
An open circuit volt age ( OCV) t o init iat e t he arc, bet w een 50 and 90V.
Welding volt age t o m aint ain t he arc during welding, bet w een 20 and 30V.
A suit able curr ent range, t ypically 30- 350A.
A st able arc. Rapid arc r ecov ery or arc r e- ignit ion wit hout current surge.
A const ant welding current . The arc lengt h m ay change during welding, but
consist ent elect r ode bur n- off rat e and weld penet rat ion charact erist ics m ust
be m aint ained during welding.
W e lding v a r ia ble s
Ot her fact ors, or w elding variables, which affect t he final qualit y of t he MMA
weld, ar e:





1 7 .4 .1
Curr ent ( am perage)
Volt age.
Trav el speed.
Polarit y.
Type of elect rode.
affect s heat I nput
Cur r e n t ( a m pe r a ge )
Am perage cont rols burn- off rat e and dept h of penet rat ion. Welding current level
is det erm ined by t he size of elect rode and t he welding posit ion - m anufact ur er s
recom m end t he norm al operat ing range and cur rent .
I ncor r ect am perage set t ings when using MMA can cont ribut e t o t he following:
Am p e r a ge t oo low
Poor fusion or penet rat ion, irregular weld bead shape, slag inclusion unst able
arc, porosit y, pot ent ial arc st rikes, difficult st art ing.
Am pe r a ge t oo high
Excessive penet rat ion, burn- t hrough, undercut , spat t er , porosit y, deep crat ers,
elect r ode dam age due t o overheat ing, high deposit ion m aking posit ional
welding difficult .
1 7 .5
Volt a ge
Open circuit volt age ( OCV) is t he volt age m easur ed bet ween t he out put
t erm inals of t he power sour ce when no curr ent is flowing t hrough t he welding
circuit .
For safet y reasons t his should not exceed 100V and is usually bet ween 50- 90V.
Arc v olt age is t he volt age r equired t o m aint ain t he arc during welding and is
usually bet ween 20–30V. As ar c v olt age is a funct ion of arc lengt h t he w elder
cont r ols t he ar c lengt h and t herefor e t he arc v olt age.
Arc volt age cont r ols weld pool fluidit y.
WI S10- 30816
MMA Welding
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Copyright © TWI Lt d
The effect s of having t he w rong arc volt age can be:
Ar c V olt a ge t oo low
Poor penet rat ion, elect rode st ubbing, lack of fusion defect s, pot ent ial for arc
st rikes, slag inclusion, unst able arc condit ion, irregular w eld bead shape.
Ar c volt a g e t oo hig h
Excessive spat t er, por osit y, arc wander, irr egular weld bead shape, slag
inclusions, fluid weld pool m aking posit ional welding difficult .
1 7 .5 .1
Tr a ve l spe e d
Trav el speed is r elat ed t o whet her t he w elding is progressed by st ringer beads
or by weaving. Oft en t he run out lengt h ( ROL) ie t he lengt h of deposit from one
st andard elect rode is quot ed on procedures rat her t han speed as it is easier for
t he welder t o visualise.
Tr a ve l spe e d t oo fa st
Nar row t hin weld
fusion/ penet rat ion.
bead,
fast
cooling,
slag
inclusions,
undercut ,
poor
Tr a ve l spe e d t oo slow
Cold lap, excess weld deposit ion, irregular bead shape, under cut .
1 7 .6
Type of cu r r e nt a nd pola r it y
Polarit y will det erm ine t he dist ribut ion of heat energy at t he w elding arc. The
preferr ed polarit y of t he MMA sy st em depends prim arily upon t he elect r ode
being used and t he desired pr opert ies of t he weld.


D ir e ct cu r r e n t . e le ct r ode posit iv e ( D CEP / D C+ ) .
Usually produces t he gr eat est penet rat ion but wit h lesser deposit ion rat e.
Known in som e st andar ds as r ev er se polarit y.
D ir e ct cu r r e n t . e le ct r ode n e ga t ive ( D CEN / D C- )
Usually produces less penet rat ion wit h great er deposit ion rat e.
Known in som e st andar ds as st raight polarit y.
When using direct curr ent t he arc can be affect ed by arc blow. The deflect ion of
t he ar c from it s norm al pat h due t o m agnet ic forces.


Alt e r n a t ing cur r e nt ( AC)
The dist ribut ion of heat energy at t he ar c is equal.
Ope r a t in g f a ct or ( O/ F)
The per cent age ( % ) of arc on t im e in a given t im e span.
When com par ed wit h sem i aut om at ic welding processes t he MMA welding
process has a low O/ F of approxim at ely 30% Manual sem i- aut om at ic MI G/ MAG
O/ F is in t he region 60% wit h fully aut om at ed MI G/ MAG in t he region of 90%
O/ F. A w elding process O/ F can be direct ly linked t o pr oduct ivit y .
Operat ing Fact or should not t o be conf use d wit h t he t erm dut y cycle , which
is a safet y value given as t he % of t im e a conduct or can carry a curr ent and is
given as a specific curr ent at 6 0 and 1 0 0 % of 10 m inut es ie 350A 60% and
300A 100% .
WI S10- 30816
MMA Welding
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Copyright © TWI Lt d
1 7 .7
Type of consu m a ble e le ct r ode
For MMA w elding t here are t hree generic t ypes of flux cov ering:
Rut ile , ba sic, ce llulosic
The det ails of t hese t ypes ar e cov er ed elsewher e in t hese not es.
1 7 .8
Typica l w e lding de fe ct s
1
Sla g inclu sions caused by poor welding t echnique or insufficient int er- run
cleaning.
2
Por osit y from using dam p or dam aged elect r odes or when welding
cont am inat ed or unclean m at erial.
3
La ck of r oot fu sion or pe ne t r a t ion caused by in- corr ect set t ings of t he
am ps, root gap or face widt h.
4
Unde r cut caused by t oo high am perage for t he posit ion or by a poor
welding t echnique eg t ravel speed t oo fast or t oo slow, ar c lengt h ( t herefore
volt age) variat ions part icularly during excessive weaving.
5
Ar c st r ik e s caused by incorr ect ar c st riking procedur e, or lack of skill.
These m ay be also caused by incorr ect ly fit t ed/ secured pow er r et urn lead
clam ps.
6
H ydr oge n cr a ck s caused by t he use of incorrect elect r ode t ype or
incorrect baking procedure and/ or cont r ol of basic coat ed elect rodes.
WI S10- 30816
MMA Welding
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Copyright © TWI Lt d
Se ct ion 1 8
Su bm e r ge d Ar c W e ldin g
18
Su bm e r ge d Ar c W e ldin g
1 8 .1
The pr oce ss
Abbreviat ed as SAW, t his is a welding process wher e an arc is st ruck bet ween a
cont inuous bare wire and t he parent plat e. The arc, elect r ode end and t he
m olt en pool ar e subm erged in an agglom erat ed or fused powder ed flux, which
t urns, int o gas and slag in it s lower layer s w hen subj ect ed t o t he heat of t he
arc, t hus pr ot ect ing t he weld from cont am inat ion.
The wire elect r ode is fed cont inuously by a feed unit of m ot or- driven rollers,
which usually are volt age- cont rolled t o ensure an arc of const ant lengt h. The
flux is fed fr om a hopper fixed t o t he welding head, and a t ube from t he hopper
spr eads t he flux in a cont inuous elongat ed m ound in front of t he arc along t he
line of t he int ended weld and of sufficient dept h t o subm erge t he arc com plet ely
so t hat t her e is no spat t er, t he weld is shielded from t he at m ospher e and t here
are no ult raviolet or infra- r ed radiat ion effect s ( see below) . Unm elt ed flux is
reclaim ed for use. The use of powder ed flux rest rict s t he pr ocess t o t he flat and
horizont al- vert ical welding posit ions.
Subm erged arc w elding is not ed for it s abilit y t o em ploy high weld curr ent s
owing t o t he propert ies and funct ions of t he flux. Such current s give deep
penet rat ion and high deposit ion rat es. Generally a DC elect rode posit ive polarit y
is em ployed up t o about 1000A because it produces a deep penet r at ion. On
som e applicat ions ( ie cladding operat ions) DC elect r ode negat ive is needed t o
reduce penet rat ion and dilut ion. At higher curr ent s or in case of m ult iple
elect r ode syst em s, AC is oft en preferr ed t o av oid t he problem of ar c blow ( when
used wit h m ult iple elect rode syst em s, DC elect r ode posit ive is used for t he lead
arc and AC is used for t he t rail arc) .
WI S10- 30816
Subm erged Arc Welding
18-1
Copyright © TWI Lt d
Pow er sources can be of t he const ant cur rent or const ant volt age t y pe eit her
m ay have out put s ex ceeding 1000A.
Difficult ies som et im es arise in ensuring conform it y of t he w eld wit h a
predet erm ined line owing t o t he obscuring effect of t he flux. Wher e possible, a
guide wheel or st ylus t o run in t he j oint prepar at ion is posit ioned in front of t he
welding head and flux hoppers or alt ernat ively a laser t racking syst em is used.
Subm erged ar c w elding is widely used in t he fabricat ion of ships, pressur e
vessels, linepipe, railway carriages and anywher e wher e long welds are
required. I t can be used t o w eld t hicknesses from 1.5m m upwards.
M a t e r ia ls j oine d





1 8 .2
Welding of carbon st eels.
Welding low alloy st eels ( eg fine grained and cr eep r esist ing) .
Welding st ainless st eels.
Welding nickel alloys.
Cladding t o base m et als t o im prov e w ear and corr osion r esist ance.
Pr oce ss va r ia ble s
Ther e ar e sev er al variables which when changed can have an effect on t he weld
appearance and m echanical propert ies:











1 8 .2 .1
Welding curr ent .
Type of flux and part icle dist ribut ion.
Arc volt age.
Trav el speed.
Elect r ode size.
Elect r ode ext ension.
Type of elect rode.
Widt h and dept h of t he layer of flux.
Elect r ode angle, ( leading, t railing) .
Polarit y.
Single- , double- or m ult i- wire syst em .
W e lding cu r r e nt
Welding current effect on weld profile ( 2.4m m elect rode diam et er, 35V arc
volt age and 610m m / m in t ravel speed)


Excessively high current produces a deep penet rat ing arc wit h a t endency t o
burn- t hrough, undercut or a high, narrow bead prone t o solidificat ion
cracking.
Excessively low curr ent produces an unst able arc, lack of penet rat ion and
possibly lack of fusion.
WI S10- 30816
Subm erged Arc Welding
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Copyright © TWI Lt d
350A
1 8 .2 .2
500A
650A
Ar c volt a ge
Arc v olt age adj ust m ent varies t he lengt h of t he arc bet ween t he elect rode and
t he m olt en weld m et al. I f t he ar c volt age increases, t he arc lengt h increases
and vice ver sa. The volt age principally det erm ines t he shape of t he w eld bead
cr oss sect ion and it s ext ernal appearance.
25V
35V
45V
Arc volt age effect on weld profile ( 2.4m m elect r ode diam et er, 500A welding
curr ent and 610m m / m in t ravel speed) .
I ncreasing t he arc v olt age will:





Produce a flat t er and wider bead.
I ncrease flux consum pt ion.
Tend t o r educe por osit y caused by rust or scale on st eel.
Help t o bridge ex cessive root opening when fit - up is poor .
I ncrease pick- up of alloying elem ent s fr om t he flux when t hey are pr esent .
Excessively high arc volt age will:





Produce a wide bead shape t hat is subj ect t o solidificat ion cracking.
Make slag rem oval difficult in groove welds.
Produce a concav e shaped fillet weld t hat m ay be subj ect t o cracking.
I ncrease under cut along t he edge( s) of fillet welds.
Ov er- alloy t he weld m et al, via t he flux.
Reducing t he arc volt age wit h const ant curr ent and t ravel speed will:

Produce a st iffer arc which im proves penet rat ion in a deep weld groov e and
resist s ar c blow.
Excessively low arc volt age will:


Produce a high, narrow bead.
Causes difficult slag rem oval along t he weld t oes.
WI S10- 30816
Subm erged Arc Welding
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Copyright © TWI Lt d
1 8 .2 .3
Tr a ve l spe e d
I f t he t rav el speed is increased:



Heat input per unit lengt h of w eld is decr eased.
Less filler m et al is applied per unit lengt h of weld, and consequent ly less
excess w eld m et al.
Penet rat ion decreases and t hus t he weld bead becom es sm aller.
300m m / m in
610m m / m in
1220m m / m in
Trav el speed effect on weld profile ( 2.4m m elect r ode diam et er , 500A welding
curr ent and 35V arc volt age) .
1 8 .2 .4
Ele ct r ode siz e
Elect r ode size affect s:


The w eld bead shape and t he dept h of penet rat ion at a given cur rent : a high
curr ent densit y result s in a st iff arc t hat penet rat es int o t he base m et al.
Conversely, a lower cur rent densit y in t he sam e size elect r ode r esult s in a
soft arc t hat is less penet rat ing.
The deposit ion rat e: at any given am perage set t ing, a sm all diam et er
elect r ode will have a higher cur rent densit y and a higher deposit ion rat e of
m olt en m et al t han a larger diam et er elect rode. However, a larger diam et er
elect r ode can car ry m ore cur rent t han a sm aller elect r ode, so t he larger
elect r ode can ult im at ely produce a higher deposit ion rat e at higher
am perage.
3.2 m m
4.0 m m
5.0 m m
Elect r ode size effect on weld profile ( 600A welding current , 30V ar c volt age and
760m m / m in t ravel speed) .
WI S10- 30816
Subm erged Arc Welding
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Copyright © TWI Lt d
1 8 .2 .5
Ele ct r ode e x t e n sion
The elect r ode ext ension is t he dist ance t he cont inuous elect rode prot rudes
beyond t he cont act t ip. At high current densit ies, resist ance heat ing of t he
elect r ode bet w een t he cont act t ip and t he arc can be ut ilised t o increase t he
elect r ode m elt ing rat e ( as m uch as 25- 50% ) . The longer t he ext ension, t he
great er t he am ount of heat ing and t he higher t he m elt ing rat e ( see below) .
30m m
1 8 .2 .6
45m m
60m m
80m m
Type of e le ct r ode
An elect r ode wit h a low elect rical conduct ivit y, such as st ainless st eel, can wit h
a norm al elect rode ext ension experience great er r esist ance heat ing. Thus for
t he sam e size elect r ode and curr ent , t he m elt ing rat e of a st ainless st eel
elect r ode will be higher t han t hat of a carbon st eel elect r ode.
1 8 .2 .7
W idt h a nd de pt h of f lux
The widt h and dept h of t he layer of granular flux influence t he appear ance and
soundness of t he finished weld as well as t he welding act ion. I f t he granular
layer is t oo deep, t he arc is t oo confined and a rough weld wit h a rope- like
appearance is likely t o result , it m ay also produce local flat areas on t he surface
oft en r eferr ed t o as gas flat s. The gases generat ed during welding cannot
readily escape, and t he surface of t he m olt en weld m et al is irregularly dist ort ed.
I f t he granular layer is t oo shallow, t he arc w ill not be ent irely subm erged in
flux. Flashing and spat t ering will occur. The w eld will have a poor appearance,
and it m ay show por osit y.
1 8 .3
St or a ge a nd ca r e of consu m a ble s
Care m ust be given t o fluxes supplied for SAW which, alt hough t hey m ay be dry
when packaged, m ay be exposed t o high hum idit y during st orage. I n such
cases t hey should be st or ed in accordance wit h t he m anufact urer's
recom m endat ions befor e use, or por osit y or cracking m ay r esult . I t rarely
pract ical or econom ical t o r e- dr y fluxes which m ay have picked up m oist ure.
Fer rous wire coils supplied as cont inuous feeding elect rodes ar e usually coppercoat ed. This provides som e cor rosion r esist ance, ensures good elect rical
cont act s and helps in sm oot h feeding. Rust and m echanical dam age should be
avoided in such product s, as t hey will bot h int errupt sm oot h feeding of t he
elect r ode. Rust will be det rim ent al t o weld qualit y generally since r ust is a
hygroscopic m at erial ( m ay cont ain or absorb m oist ure) and t hus it can lead t o
hydrogen induced cracking.
Cont am inat ion by carbon cont aining m at erials such as oil, grease, paint and
drawing lubricant s is especially harm ful wit h ferr ous m et als. Carbon pick- up in
t he weld m et al can cause a m ark ed and usually undesirable change in
propert ies. Such cont am inant s m ay also result in hydrogen being absorbed in
t he weld pool.
Welders should always follow t he
consum ables st orage and handling.
WI S10- 30816
Subm erged Arc Welding
18-5
m anufact urer's
r ecom m endat ions
for
Copyright © TWI Lt d
Se ct ion 1 9
TI G W e ldin g
19
TI G W e ldin g
1 9 .1
Pr oce ss ch a r a ct e r ist ics
I n t he USA t he TI G process is also called gas t ungst en arc w elding ( GTAW) . TI G
welding is a pr ocess w her e m elt ing is produced by heat ing wit h an arc st ruck
bet ween a non- consum able t ungst en elect r ode and t he workpiece.
An inert gas is used t o shield t he elect rode and weld zone t o pr ev ent oxidat ion
of t he t ungst en elect rode and at m ospheric cont am inat ion of t he weld and hot
filler wire ( as shown below) .
Figur e 1 9 .1 M a n ua l TI G w e lding.
Tungst en is used because it has a m elt ing point of 3370°C, which is well above
any ot her com m on m et al.
The power source is of t he const ant cur r ent t ype.
1 9 .2
Pr oce ss va r ia ble s
The m ain variables in TI G w elding are:
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Welding curr ent .
Curr ent t ype and polarit y.
Trav el speed.
Shape of t ungst en elect rode t ip and vert ex angle.
Shielding gas flow rat e.
Each of t hese variables is considered in m ore det ail in t he following subsect ions.
WI S10- 30816
TI G Welding
19-1
Copyright © TWI Lt d
1 9 .2 .1
W e lding cu r r e nt
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1 9 .2 .2
Cur r e nt t ype a nd pola r it y
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1 9 .2 .3
Wit h st eels DC elect r ode negat ive is used.
Mat erials which have refract ory oxides such as t hose of alum inium or
m agnesium are welded using AC or DC elect r ode posit ive which break up
t he oxide layer.
Wit h a DC posit ively connect ed elect r ode, heat is concent rat ed at t he
elect r ode t ip and t herefor e for DC posit ive welding t he elect rode needs t o be
of gr eat er diam et er t han when using DC negat ive if overheat ing of t he
t ungst en is t o be av oided. A wat er- cooled t or ch is r ecom m ended if DC
posit ive is used.
The curr ent carr ying capacit y of a DC posit ive elect r ode is about one t ent h
t hat of a negat ive one and it is t herefor e lim it ed t o w elding t hin sect ions.
Tr a ve l spe e d
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1 9 .2 .4
Weld penet rat ion is direct ly relat ed t o welding curr ent .
I f t he w elding current is t oo low, t he elect r ode t ip will not be properly
heat ed and an unst able arc m ay result .
I f t he welding current is set t oo high, t he elect rode t ip m ight overheat and
m elt , leading t o t ungst en inclusions.
Trav el speed affect s bot h weld widt h and penet r at ion but t he effect on widt h
is m ore pr onounced t han on penet rat ion.
I ncreasing t he t rav el speed r educes t he penet rat ion and widt h.
Reducing t he t ravel speed increases t he penet r at ion and widt h.
Tu n gst e n e le ct r ode t ype s
Differ ent t ypes of t ungst en elect rodes can be used t o suit different applicat ions:

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WI S10- 30816
TI G Welding
Pur e t un gst e n elect r odes ar e rar ely used.
Thor ia t e d e le ct r ode s ar e alloyed wit h t horium oxide, t ypically 2% , t o
im prove arc init iat ion. They have higher cur r ent car rying capacit y t han pure
t ungst en elect r odes and m aint ain a sharp t ip for longer. Unfort unat ely,
t horia is slight ly radioact ive ( em it t ing α radiat ion) and t he dust generat ed
during t ip grinding should not be inhaled. Elect r ode grinding m achines used
for t horiat ed t ungst en grinding should be fit t ed wit h a dust ext r act ion
syst em .
Ce r ia t e d a n d la n t h a n a t e d e le ct r ode s ar e alloyed wit h cerium and
lant hanum oxides, for t he sam e r eason as t horiat ed elect rodes. They
operat e successfully wit h DC or AC but since cerium and lant hanum are not
radioact ive, t hese t ypes have been used as replacem ent s for t horiat ed
elect r odes
Zir con ia t e d e le ct r ode s ar e alloyed wit h zirconium oxide. Oper at ing
charact erist ics of t hese elect r odes fall bet ween t he t horiat ed t ypes and pure
t ungst en. How ev er, since t hey ar e able t o ret ain a balled end during
welding, t hey are recom m ended for AC welding. Also, t hey have a high
resist ance t o cont am inat ion and so t hey are used for high int egrit y welds
wher e t ungst en inclusions m ust be av oided.
19-2
Copyright © TWI Lt d
1 9 .2 .5
Sha pe of t ungst e n e le ct r ode t ip
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Wit h DC elect rode negat ive, t horiat ed, ceriat ed or lant hanat ed t ungst en
elect r odes ar e used wit h t he end is ground t o a specific angle ( t he elect rode
t ip angle or v ert ex angle – shown below) .
As a general rule, t he lengt h of t he ground port ion of t he t ip of t he elect rode
should have a lengt h equal t o approxim at ely 2- 2.5 t im es t he elect rode
diam et er.
The t ip of t he elect r ode is ground flat t o m inim ise t he risk of t he t ip
breaking off when t he arc is init iat ed or during welding ( shown below) .
I f t he vert ex angle is incr eased, t he penet rat ion increases.
I f t he vert ex angle is decr eased, bead widt h increases.
For AC w elding, pure or zirconiat ed t ungst en elect rodes ar e used.
These are used wit h a hem ispherical ( ‘balled’) end ( as shown below) .
I n order t o pr oduce a balled end t he elect r ode is grounded, an ar c init iat ed
and t he cur rent incr eased unt il it m elt s t he t ip of t he elect rode.
Elect rode t ip angle
( or vert ex angle)
Elect rode t ip wit h
wit h flat end
Elect rode t ip wit h a
balled end
Figur e 1 9 .2 Ex a m ple s of sha pe s of e le ct r ode t ips.
1 9 .3
Fille r w ir e s a nd sh ie lding ga se s
These ar e select ed on t he basis of t he m at erials being welded. See t he relevant
chapt er in t hese not es.
1 9 .4
Tungst e n inclu sions
Sm all fragm ent s of t ungst en t hat ent er a weld will always show up on
radiographs ( because of t he relat ively high densit y of t his m et al) and for m ost
applicat ions will not be accept able.
Therm al shock t o t he t ungst en causing sm all fragm ent s t o ent er t he weld pool
is a com m on cause of t ungst en inclusions and is t he reason why m odern power
sour ces hav e a cur rent slope- up device t o m inim ise t his risk.
This device allows t he curr ent t o rise t o t he set value over a short period and so
t he t ungst en is heat ed m or e slowly and gent ly.
WI S10- 30816
TI G Welding
19-3
Copyright © TWI Lt d
1 9 .5
Cr a t e r cr a ck ing
Crat er cracking is one form of solidificat ion cracking and som e filler m et als can
be sensit ive t o it .
Modern pow er sour ces have a curr ent slope- out device so t hat at t he end of a
weld when t he welder swit ches off t he cur rent it reduces gradually and t he weld
pool get s sm aller and shallower.
This m eans t hat t he weld pool has a m ore favourable shape when it finally
solidifies and crat er cr acking can be avoided.
1 9 .6
Com m on a pplica t ions of t he TI G pr oce ss
These include aut ogenous welding of longit udinal seam s, in t hin walled pipes
and t ubes, in st ainless st eel and ot her alloys, on cont inuous form ing m ills.
Using filler wires, TI G is used for m aking high qualit y j oint s in heavier gauge
pipe and t ubing for t he chem ical, pet roleum and pow er generat ing indust ries.
I t is also in t he aerospace indust ry for such it em s as airfram es and rock et
m ot or cases.
1 9 .7
Adv a nt a ge s of t he TI G pr oce ss
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1 9 .8
I t produces superior qualit y welds, wit h ver y low lev els of diffusible
hydrogen and so t here is less danger of cold cracking.
I t does not give w eld spat t er nor slag inclusions which m akes it part icularly
suit able for applicat ions t hat r equire a high degr ee of cleanliness ( eg
pipework for t he food and drinks indust ry, sem i- conduct ors m anufact uring,
et c) .
I t can be used wit h filler m et al and on t hin sect ions wit hout filler; it can
produce w elds at r elat ively high speed.
I t enables welding variables t o be accurat ely cont r olled and is part icularly
good for cont r olling weld root penet r at ion in all posit ions of w elding.
I t can be used t o w eld alm ost all weldable m et als, including dissim ilar j oint s,
but is not generally used for t hose wit h low m elt ing point s such as lead and
t in. The m et hod is especially useful in welding t he react ive m et als wit h very
st able oxides such as alum inium , m agnesium , t it anium and zirconium .
The heat source and filler m et al addit ions are cont r olled independent ly and
t hus it is very good for j oining t hin base m et als.
D isa dv a n t a ge s of t h e TI G pr oce ss
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WI S10- 30816
TI G Welding
I t gives low deposit ion rat es com par ed wit h ot her ar c w elding processes.
Ther e is a need for higher dext erit y and welder co- ordinat ion t han wit h
MI G/ MAG or MMA w elding.
I t is less econom ical t han MMA or MI G/ MAG for sect ions t hicker t han
~ 10m m .
I t is difficult t o fully shield t he weld zone in dr aught y condit ions and so m ay
not be suit able for sit e/ field welding.
Tungst en inclusions can occur if t he elect rode is allowed t o cont act t he weld
pool.
The process does not have any cleaning act ion and so has low t olerance for
cont am inant s on filler or base m et als.
19-4
Copyright © TWI Lt d
Se ct ion 2 0
W e ldin g Re pa ir s
20
W e ld Re pa ir s
Weld repairs can be divided int o t wo specific areas:
1
2
Product ion r epairs.
I n service r epairs.
The r easons for m aking a repair are m any and varied. Typically, t hey range
from t he r em oval of w eld defect s induced dur ing m anufact ure t o a quick and
t em porar y running- repair t o an it em of product ion plant . I n t hese t erm s, t he
subj ect of w elding repairs is also wide and varied and oft en confused wit h
m aint enance and refurbishm ent where t he w ork can be scheduled.
Wit h planned m aint enance and r efurbishm ent , sufficient t im e can be allowed t o
enable t he t asks t o be com plet ed wit hout product ion pressur es being applied.
I n cont rast , repairs are usually unplanned and m ay result in short cut s being
t aken t o allow t he product ion program m e t o cont inue. I t is, t herefore, advisable
for a fabricat or t o hav e an est ablished policy on r epairs and t o have repair
m et hods and pr ocedur es in place.
The m anually cont rolled welding processes are t he easiest t o use, part icularly if
it is a local repair or one t o be car ried out on- sit e. Probably t he m ost frequent ly
used of t hese processes is m anual m et al arc ( MMA) as t his is versat ile, port able
and readily applicable t o m any alloys because of t he wide range of off- t he- shelf
consum ables. Repairs alm ost always result in higher r esidual st resses and
increased dist ort ion com pared wit h first t im e welds. Wit h carbon- m anganese
and low/ m edium alloy st eels, t he applicat ion of preheat and post - w eld heat
t reat m ent s m ay be r equired.
Ther e ar e a num ber of key fact or s t hat need t o be consider ed befor e
undert aking any repair.
The m ost im port ant being a j udgem ent as t o whet her it is financially
wort hwhile. Befor e t his j udgem ent can be m ade, t he fabricat or needs t o answ er
t he following quest ions:
1
2
3
4
5
Can st ruct ural int egrit y be achiev ed if t he it em is r epaired?
Are t her e any alt ernat ives t o w elding?
What caused t he defect and is it likely t o happen again?
How is t he defect t o be rem ov ed and what w elding process is t o be used?
Which non- dest ruct ive t est ing ( NDT) is r equired t o ensur e com plet e
rem oval of t he defect ?
6 Will t he welding procedures r equire appr oval/ re- approval?
7 What will be t he effect of welding dist ort ion and residual st ress?
8 Will heat t reat m ent be r equired?
9 What NDT is required and how can accept abilit y of t he repair be
dem onst rat ed?
10 Will approval of t he r epair be r equired - if yes, how and by whom ?
Alt hough a weld repair m ay be a r elat ively st raight forward act ivit y, in m any
inst ances it can be quit e com plex and various engineering disciplines m ay need
t o be involved t o ensur e a successful out com e.
I t is recom m ended t hat t here be an ongoing analysis of t he t ypes of defect
car ried out by t he Q/ C depart m ent t o discover t he likely reason for t heir
occurr ence, ( Mat erial/ process or skill relat ed.)
WI S10- 30816
Weld Repairs
20-1
Copyright © TWI Lt d
I n general t erm s, a welding repair involves:
1
A det ailed assessm ent t o find out t he ext r em it y of t he defect . This m ay
involve t he use of a surface or sub- surface NDT m et hods.
2 Cleaning t he repair ar ea, ( r em oval of paint grease et c) .
3 Once est ablished t he ex cavat ion sit e m ust be clearly ident ified and m arked
out .
4 An ex cavat ion procedur e m ay be r equired ( m et hod used ie grinding, ar c- air
gouging, preheat requirem ent s et c) .
5 NDT should be used t o locat e t he defect and confirm it s rem oval.
6 A welding repair procedur e/ m et hod st at em ent wit h t he appropr iat e*
welding process, consum able, t echnique, cont r olled heat input and
int erpass t em per at ures et c will need t o be appr ov ed.
7 Use of appr ov ed w elder s.
8 Dressing t he weld and final visual.
9 NDT pr ocedur e/ t echnique pr epar ed and carried out t o ensur e t hat t he
defect has been successfully rem oved and r epaired.
10 Any post r epair heat t r eat m ent r equirem ent s.
11 Final NDT procedure/ t echnique prepared and carried out aft er heat
t reat m ent r equirem ent s.
12 Applying prot ect ive t r eat m ent s ( paint ing et c as required) .
( * Appropriat e’ m eans suit able for t he alloys being repaired and m ay not apply
in specific sit uat ions)
2 0 .1
Pr oduct ion r e pa ir s
Repairs are usually ident ified during product ion inspect ion and evaluat ion of t he
report s is usually carr ied out by t he Welding I nspect or , or NDT operat or.
Discont inuit ies in t he welds are only classed as defect s when t hey ar e out side
t he perm it t ed range per m it t ed by t he applied code or st andard.
Befor e t he r epair can com m ence, a num ber of elem ent s need t o be fulfilled.
2 0 .1 .1
An a ly sis
As t his defect is surface br eaking and has occurr ed at t he fusion face t he
problem could be cracking or lack of sidewall fusion. I f t he defect is found t o be
cracking t he cause m ay be associat ed wit h t he m at erial or t he welding
procedur e, however if t he defect is lack of sidewall fusion t his can be
apport ioned t o t he lack of skill of t he welder .
2 0 .1 .2
Asse ssm e nt
I n t his part icular case as t he defect is open t o t he surface, m agnet ic part icle
inspect ion ( MPI ) or dy e penet rant inspect ion ( DPI ) m ay be used t o gauge t he
lengt h of t he defect and ult rasonic t est ing ( U/ T) used t o gauge t he dept h.
WI S10- 30816
Weld Repairs
20-2
Copyright © TWI Lt d
A t ypical defect is show n below:
Plan view of defect
2 0 .1 .3
Ex ca va t ion
I f a t herm al m et hod of excavat ion is being used ie arc- air gouging it m ay be a
requirem ent t o qualify a procedur e as t he heat generat ed m ay have an affect
on t he m et allurgical st ruct ure, r esult ing in t he risk of cracking in t he weld or
parent m at erial
To prevent cracking it m ay be necessary t o apply a preheat .
The dept h t o widt h rat io shall not be less t han 1 ( dept h) t o 1 ( widt h) ideally 1
t o 1.5 would be r ecom m ended ( rat io: dept h 1 t o t he widt h 1.5) .
WI S10- 30816
Weld Repairs
20-3
Copyright © TWI Lt d
Side view of ex cavat ion for slight sub surface defect .
W
D
Side view of ex cavat ion for deep defect .
W
D
Side view of ex cavat ion for full root r epair.
W
D
WI S10- 30816
Weld Repairs
20-4
Copyright © TWI Lt d
2 0 .1 .4
Cle a n ing of t he e x ca v a t ion
At t his st age grinding of t he repair area is im port ant , due t o t he risk of carbon
becom ing im pregnat ed int o t he w eld m et al/ parent m at erial.
I t should be gr ound back t ypically 3- 4m m t o bright m et al.
Con f ir m a t ion of e x ca va t ion
At t his st age NDT should be used t o confirm t hat t he defect has been
com plet ely ex cavat ed fr om t he ar ea.
WI S10- 30816
Weld Repairs
20-5
Copyright © TWI Lt d
2 0 .1 .5
Re - w e lding of t he e x ca va t ion
Prior t o re- w elding of t he excavat ion a det ailed repair welding procedur e/
m et hod st at em ent shall be approved.
Typical side view of w eld repair
2 0 .1 .6
N D T con fir m a t ion of su cce ssfu l r e pa ir
Aft er t he ex cavat ion has been filled t he weldm ent should t hen undergo a
com plet e r et est using t he sam e NDT t echniques as pr eviously used t o est ablish
t he original repair, t his is carried out t o ensure no furt her defect s have been
int roduced by t he repair welding process. NDT m ay also need t o be furt her
applied aft er any addit ional post - weld heat t reat m ent has been car ried out .
2 0 .2
I n- se r v ice r e pa ir s
Most in- service r epairs can be of a very com plex nat ure, as t he com ponent is
very likely t o be in a different w elding posit ion and condit ion t han it was during
product ion. I t m ay also have been in cont act wit h t oxic or com bust ible fluids
hence a perm it t o w or k will need t o be sought prior t o any work being car ried
out . The r epair welding procedur e m ay look ver y different t o t he original
product ion pr ocedure due t o changes in t hese elem ent s.
Ot her fact or s m ay also be t ak en int o consider at ion, such as t he effect of heat
on any sur rounding areas of t he com ponent ie elect rical com ponent s, or
m at erials t hat m ay becom e dam aged by t he r epair procedur e. This m ay also
include difficult y in carr ying out any required pre- or post - welding heat
t reat m ent s and a possible rest rict ion of access t o t he area t o be repaired. For
large fabricat ions it is likely t hat t he repair m ust also t ak e place on- sit e and
wit hout a shut down of operat ions, which m ay bring ot her elem ent s t hat need
t o be considered.
Repair of in service defect s m ay require considerat ion of t hese and m any ot her
fact ors, and as such ar e generally considered m or e com plicat ed t han pr oduct ion
repairs.
Joining t echnologies oft en play a vit al role in t he repair and m aint enance of
st ruct ur es. Part s can be replaced, worn or cor roded part s can be built up, and
cracks can be r epaired.
WI S10- 30816
Weld Repairs
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Copyright © TWI Lt d
When a r epair is required it is im port ant t o det erm ine t wo t hings: first ly, t he
reason for failure and, secondly, can t he com ponent act ually be repaired? The
lat t er point infers t hat t he m at erial t ype is known. For m et als, part icularly t hose
t o be welded, t he chem ical com posit ion is vit ally im port ant . Failure m odes oft en
indicat e t he approach r equired t o m ake a sound repair. When t he cause- effect
analysis, however sim ple, is not followed t hrough it is oft en t he case t hat t he
repair is unsafe - som et im es disast rously so.
I n m any inst ances, t he St andard or Code used t o design t he st ruct ure will
define t he t ype of r epair t hat can be car ried out and will also give guidance on
t he m et hods t o be followed. St andards im ply t hat when designing or
m anufact uring a new product it is im port ant t o consider a m aint enance regim e
and repair procedures. Repairs m ay be r equired during m anufact ure and t his
sit uat ion should also be consider ed.
Nor m ally, t here is m or e t han one way of m aking a repair. For exam ple, cracks
in cast iron m ight be held t oget her or r epaired by: pinning, bolt ing, rivet ing,
welding, or brazing. The m et hod chosen will depend on fact ors such as t he
reason for t he failure, t he m at erial com posit ion and cleanliness, t he
environm ent and t he size and shape of t he com ponent .
I t is ve r y im por t a nt t hat repair and m aint enance w elding are not r egarded as
act ivit ies, which are sim ple or st raight forward. I n m any inst ances a r epair m ay
seem undem anding but t he consequences of get t ing it wrong can be
cat ast r ophic failure wit h disast rous consequences.
I s w e lding t he be st m e t hod of r e pa ir ?
I f repair is called for because a com ponent has a local irregularit y or a shallow
defect , grinding out any defect s and blending t o a sm oot h cont our m ight well be
accept able. I t will cert ainly be preferable if t he st eel has poor weldabilit y or if
fat igue loading is severe. I t is oft en bet t er t o reduce t he so- called fact or of
safet y slight ly, t han t o risk put t ing defect s, st r ess concent rat ions and residual
st resses int o a brit t le m at erial.
I n fact brit t le m at erials - which can include som e st eels ( part icularly in t hick
sect ions) as well as cast irons - m ay not be able t o wit hst and t he residual
st resses im posed by heavy w eld repairs, par t icularly if defect s ar e not all
rem ov ed, leaving st r ess concent rat ions t o init iat e cracking.
I s t he r e pa ir r e a lly lik e e a r lie r r e pa ir s?
Repairs of one sort m ay have been rout ine for m any years. I t is im port ant ,
howev er, t o check t hat t he next one is not subt ly differ ent . For exam ple, t he
sect ion t hickness m ay be gr eat er; t he st eel t o be r epaired m ay be different and
less weldable, or t he rest raint higher. I f t her e is any doubt , answer t he
rem aining quest ions.
W ha t is t h e com posit ion a nd w e lda bilit y of t he ba se m e t a l?
The original drawings will usually give som e idea of t he st eel involved, alt hough
t he specificat ion lim it s m ay t hen have been less st ringent , and t he specificat ion
m ay not give enough com posit ional det ails t o be helpful. I f sulphur- bearing
fr ee- m achining st eel is involved, it could give hot cracking problem s during
welding.
WI S10- 30816
Weld Repairs
20-7
Copyright © TWI Lt d
I f t here is any doubt about t he com posit ion, a chem ical analysis should be
car ried out . I t is im port ant t o analyse for all elem ent s, which m ay affect
weldabilit y ( Ni, Cr, Mo, Cu, V, Nb and B) as well as t hose usually, specified ( C,
S, P, Si and Mn) .
A sm all cost spent on analysis could prev ent a valuable com ponent being ruined
by ill- prepared r epairs or, sav e m oney by reducing or avoiding t he need for
preheat if t he com posit ion were leaner t han ex pect ed. Once t he com posit ion is
known, a welding procedure can be devised.
W h a t st r e n gt h is r e qu ir e d fr om t h e r e pa ir ?
The higher t he yield st rengt h of t he repair w eld m et al, t he great er will be t he
residual st ress level on com plet ion of welding, t he great er t he risk of cracking,
t he great er t he clam ping needed t o av oid dist ort ion and m or e difficult y in
for m ulat ing t he welding procedur e. I n any case, t he pract ical lim it for t he yield
st rengt h of conv ent ional st eel weld m et als is about 1000N/ m m 2 .
Ca n pr e h e a t be t ole r a t e d?
Not only does a high lev el of preheat m ak e condit ions m or e difficult for t he
welder; t he par ent st eel can be dam aged if it has been t em pered at a low
t em perat ur e. I n ot her cases t he st eel being repaired m ay cont ain it em s, which
are dam aged by ex cessive heat ing. Preheat lev els can be r educed by using
consum ables of ult ra- low hydrogen cont ent or by non- fer rit ic weld m et als. Of
t hese, aust enit ic elect rodes m ay need som e preheat , but t he m or e expensive
nickel alloys usually do not . However, t he lat t er m ay be sensit ive t o high
sulphur and phosphorus cont ent s in t he par ent st eel if dilut ed int o t he weld
m et al.
Ca n soft e ning
be t ole r a t e d?
or
ha r de n in g
of
t he
heat
a ff e ct e d
z on e
( H AZ)
Soft ening of t he HAZ is likely in ver y high st rengt h st eels, part icularly if t hey
have been t em per ed at low t em perat ur es. Such soft ening cannot be avoided,
but it s ext ent can be m inim ised. Hard HAZs are part icularly vulnerable wher e
service condit ions can lead t o st ress cor rosion. Solut ions cont aining H 2 S
( hydrogen sulphide) m ay dem and hardness’ below 248HV ( 22HRC) alt hough
fr esh aerat ed seawat er appear s t o t olerat e up t o about 450HV. Ex cessively hard
HAZ’s m ay , t herefor e, r equire post - weld heat t r eat m ent ( PWHT) t o soft en t hem
but provided cracking has been av oided.
I s PW H T pr a ct ica ble ?
Alt hough it m ay be desirable, PWHT m ay not be possible for t he sam e reasons
t hat preheat ing is not possible. For large st ruct ures, local PWHT m ay be
possible, but car e should be t aken t o abide by t he r elevant codes, because it is
all t oo easy t o int roduce new residual st resses by im properly ex ecut ed PWHT.
I s PW H T ne ce ssa r y?
PWHT m ay be needed for one of sev eral reasons, and t he reason m ust be
known befor e considering whet her it can be av oided.
W ill t h e f a t igue r e sist a nce of t he r e pa ir be a de qu a t e ?
I f t he r epair is in an area, which is highly st ressed by fat igue, and part icularly if
t he at t em pt ed r epair is of a fat igue crack, inferior fat igue life can be expect ed
unless t he weld surface is ground sm oot h and no surface defect s are left . Fillet
welds, in which t he root cannot be ground sm oot h, are not t olerable in ar eas of
high fat igue st r ess.
WI S10- 30816
Weld Repairs
20-8
Copyright © TWI Lt d
W ill t h e r e pa ir r e sist it s e nvir onm e nt ?
Besides cor rosion, it is im port ant t o consider t he possibilit y of st r ess cor rosion,
corr osion fat igue, t herm al fat igue and oxidat ion in service.
Cor rosion and oxidat ion r esist ance usually requires t hat t he com posit ion of t he
filler m et al is at least as noble or oxidat ion resist ant as t he parent m et al. For
corr osion fat igue r esist ance, t he repair w eld profile m ay need t o be sm oot hed.
To r esist st r ess cor rosion, PWHT m ay be necessary t o rest ore t he cor r ect
m icrost ruct ure, reduce hardness and reduce t he residual st ress left by t he
repair.
Ca n t h e r e pa ir be in spe ct e d a n d t e st e d?
For onerous service, radiography and/ or ult rasonic ex am inat ion are oft en
desirable, but problem s are likely if st ainless st eel or nickel alloy filler is used;
m or eover, such r epairs cannot be assessed by m agnet ic part icle inspect ion. I n
such cases, it is part icularly im port ant t o car ry out t he pr ocedural t est s for
repairs v ery crit ically, t o ensure t hat t here are no risks of cracking and no
likelihood of serious w elder- induced defect s.
I ndeed, for all repair welds, it is vit al t o ensur e t hat t he w elders ar e properly
m ot ivat ed and car efully super vised.
As- w e lde d r e pa ir s
Repair wit hout PWHT is, of cour se, norm al wher e t he original weld was not heat
t reat ed, but som e alloy st eels and m any t hick- sect ioned com ponent s requir e
PWHT t o m aint ain a reasonable level of t oughness, cor rosion resist ance et c.
How ev er, PWHT of com ponent s in service is not always easy or ev en possible,
and local PWHT m ay give rise t o m or e pr oblem s t han it solves except in sim ple
st ruct ur es.
WI S10- 30816
Weld Repairs
20-9
Copyright © TWI Lt d
Repair Considerations
 The first thing to consider, is it worth repairing?
 Repair welding can cost up to ten times the original cost
of making the weld, that’s if it all goes according to
plan.
 There could be access issues, contamination issues if it’s
in service.
 There could be metallurgical issues, changing properties
etc.
 It may be more cost efficient to replace the component
or cut the weld out completely.
 Try and establish the reason for defect occurrence as
this may determine a change to the procedure or re
training.
 Was the defect due to poor fit up conditions,
misalignment.
Weld Repairs
Section 20
Copyright © TWI Ltd
Cost of Weld Repairs
Original weld
Cost
Repair weld
Cut, prep, tack
£
Inspector Repair report (NCR etc)
Extra cost
££
Welder time
£
Inspector Identify repair area
££
Consumable & gas
£
Inspector Mark out repair area
££
Visual inspection
£
Welder Remove defect
££
NDT
££
Inspector Visual inspection of excavation
££
Documentation
£
Inspector NDT area of excavation
££
Inspector Monitor repair welding
££
Welder time
£
Consumable & gas
£
Inspector Visual inspection
££
NDT
££
Extra repair Documentation
£
Penalty % NDT
££
Copyright © TWI Ltd
Repair Considerations
 Can pre heat be tolerated.
 Local pre heat and welding could lead to
distortion and residual stress.
 In service repairs more complex, electrical and
combustible material issues, contamination.
 Production repairs less complex.
 Approved repair procedure and welder.
 Mark accurately where material must be
removed.
Copyright © TWI Ltd
Investigation
What is the nature of the defect?
 If the defect can be attributed to
workmanship, it may not require further
investigation.
 However, if it is some form of cracking, it will
require further investigation as the problem
may be repeated during the repair.
Copyright © TWI Ltd
Copyright © TWI Ltd
Investigation
How was the defect detected?
 Visual.
 Dye Penetrant.
 Magnetic particle.
 Radiography.
 Ultrasonics.
 These processes are not always 100%
accurate.
 Human error etc.
Copyright © TWI Ltd
20‐1
Where is the Defect?
 Defects found on the surface by a NDT method
that is surface only, may require further
investigation using sub surface NDT.
 Remove defect and investigate further.
 Internal defects will be found with UT or
X-Ray.
 UT, will be able to size and locate defect far
better than X-Ray.
What is the Defect?
The process can help determine defect?
 A sub surface NDT method can help establish
defect type with good interpretation.
 Porosity tends to be central in the weld and at
restarts and finishes.
 Slag inclusions and lack of fusion defects tend
to be between runs and at the side walls of
the original preparation.
Copyright © TWI Ltd
What is the Defect?
Copyright © TWI Ltd
What is the Defect?
Copyright © TWI Ltd
Removing Material
 Depending on the material, gouging,
machining, filing, grinding can be used, pencil
type de burrs for more intricate work.
 A greater area than just the defect area will
have to be removed to allow for access and
promote good fusion characteristics.
 If the depth of defect is not known,
progressively remove material and NDT.
check.
Copyright © TWI Ltd
Copyright © TWI Ltd
Weld Repairs
Plan View of defect
Copyright © TWI Ltd
20‐2
Production Weld Repairs
Arc Air Gouging
Side view of defect excavation
D
Side view of repair welding
Copyright © TWI Ltd
Preparation of Weld Repairs
 The shape of the repaired area is very
important.
 A boat type shape with large radius is
preferred to allow good access and prevent
any lack of fusion defects which could occur
with straight edges.
Copyright © TWI Ltd
Considerations Before Welding
 Pre heat, ref original procedure.
 Distortion control measures, this could be
quite dramatic as the heat concentration will
generally be very localised.
 Materials such as S/S may require back
purging; pipes etc.
 Process to use, TIG is probably the most
versatile but there may be consumable match
issues.
Copyright © TWI Ltd
Copyright © TWI Ltd
Preparation of Weld Repairs
Ideal repair shape
Potential for lack of
fusion defects
Copyright © TWI Ltd
Upon Completion
 PWHT to remove residual stress and/or
hydrogen release.
 The repair may need dressing to give it the
same geometry as the rest of the weld.
 Inspection of finished repair including NDT as
original process used.
 Pressure testing if required.
Copyright © TWI Ltd
20‐3
Repairs
You are working as a Senior Welding Inspector
on a high pressure gas supply pipe line.
The pipe has a wall thickness of 12mm and in
certain areas 25mm. The pipe is a 24”
longitudinal seamed X60 grade, welded with the
SAW process.
All circumferential seams are welded with an
E6010 electrode for the root and hot pass, fillers
and capping E8010 electrode, all passes in the
PF position.
Copyright © TWI Ltd
Question 2
While witnessing a weld repair on a circumferential
welded joint, the fabricator uses a preheat of
200°C. Would this pre heat temperature be correct
in accordance with the TWI Specification?
a. No, only 75°C preheats shall be used
b. Yes providing the original preheat applied to the
circumferential joint was 200°C
c. Yes, providing the original preheat applied to
the circumferential joint was 125°C
d. No, preheats aren’t permitted for repair welds
on the circumferential seams
Copyright © TWI Ltd
Question 4
Question 1
One of the circumferential seams has a linear slag
inclusion 450mm in length and has been detected by
radiography. Can this defect be repaired in accordance
with the TWI Specification?
a. This defect can be repaired providing the welding is
conducted in the same direction as the original welding
and under constant supervision
b. Any defect exceeding 450mm in length cant be
repaired in accordance with the TWI Specification
c. This defect can be welded in accordance with the TWI
specification, but must be welded using a basic type
electrode and under constant supervision
d. All options are incorrect
Copyright © TWI Ltd
Question 3
One of your welding inspectors reports back to you that a
weld repair has been removed using the arc air gouging
process. Is this acceptable in accordance with the TWI
Specification?
a. No, defective areas shall be removed by thermal
cutting, grinding back to clean metal and inspected by
MPI before commencement of welding
b. Yes, providing the gouged area is cleaned by grinding
back to clean metal, inspected by PT before
commencement of welding
c. Yes, providing the gouged area is cleaned by grinding
back to clean metal, then visual inspection before the
commencement of welding
d. All options are incorrect
Copyright © TWI Ltd
Question 5
You notice that no weld repair procedures have
been approved for this pipeline. In this situation
would you permit any repairs to be conducted?
One of your inspectors reports back to you that a
crack has been repaired in Weld 42, section 34.
Which of the following statements are correct?
a. Yes, providing all weld repairs are conducted in
accordance with the TWI Specification
b. Yes, providing that all welders are qualified to
conduct the repairs
c. No, all repair welding shall have an approved
welding repair procedure
d. No, repairs aren’t generally conducted on
pipelines; any defects detected would normally
require the entire weld to be removed
a. This would not be permitted, as cracks can’t be
repaired in accordance with the TWI Specification
b. This would be permitted providing the crack
didn’t exceed the maximum repairable defect
length
c. This would be permitted providing the repair has
be carried out in accordance with the approved
repair WPS
d. A crack like defect can’t occur using the
electrodes stated
Copyright © TWI Ltd
Copyright © TWI Ltd
20‐4
Question 6
Question 7
After conducting a repair a slag inclusion that exceeds the
maximum permitted length has been detected by
radiography. The fabricator requests approval from you to
conduct a weld repair in this defective area. Would you
permit this repair?
One of your welding inspectors informs you that
a weld repair has been conducted without a
qualified welding inspector present. In this
situation which of the following applies?
a. Yes, a repair can be conducted on this type of defect in
accordance with the TWI Specification
b. No, weld repairs are not permitted in accordance with
the TWI Specification
c. The TWI Specification makes no reference to this
situation; you would need to ask advice on this
situation
d. No, in this situation the entire weld would have to be
removed, a cutout
a. This is not permitted by the TWI Specification
b. Providing the welder is qualified this is
acceptable in accordance with the TWI
Specification
c. Providing the welder informs you that the
approved repair WPS has been strictly
adhered to this is acceptable
d. No options are correct
Copyright © TWI Ltd
Question 8
You suspect that lack of inter run fusion has
occurred during the welding of one of the pipes
to pipe circumferential seams. Which of the
following NDT methods would best detect this
defect
a. MPI or DPI as this defect is usually surface
breaking
b. RT would be best suited to detect this defect
if no slag was present
c. UT would be best suited to detect this defect
if no slag was present
d. 2 options are correct
Copyright © TWI Ltd
Copyright © TWI Ltd
Question 9
Some codes and standards only permit weld
repairs to be conducted for a minimum amount of
times before a full cut out is required. Why do you
think this is the case?
a. If a weld is repaired an unlimited amount of
times it may affect the mechanical and
metallurgical properties of the weld
b. The amount of preheat will be too high for the
welder to weld
c. A critical post heat treat will always be required
d. It would be difficult to find approved welders to
conduct these type of repairs
Copyright © TWI Ltd
Question 10
One of your welding inspectors asks you what is
the minimum depth a weld repair excavation
needs to be. Which of the following would be
your answer?
a. The thickness of the base material.
b. As deep as it is required to ensure the defect
has been fully removed
c. The depth would depend on the radiography
interpretation report
d. 2 options are correct
Copyright © TWI Ltd
20‐5
Appendix 1
Homework
Senior Welding Inspection: Multiple Choice Questions
Paper 1
Name: ……………………………….…………………………. Date: ……………………
1
Which is the best destructive test for showing lack of sidewall fusion in a 25mm
thickness butt weld?
a
b
c
d
2
Which of the following would be cause for rejection by most fabrication standards
when inspecting fillet welds with undercut, a small amount of?
a
b
c
d
3
EN
EN
EN
EN
ISO 15614.
ISO 2560.
287.
ISO 17637.
Excess weld metal height.
Start porosity.
Spatter.
Arc strikes.
Which of the following is a planar imperfection?
a
b
c
d
6
BS
BS
BS
BS
When visually inspecting the face of a finished weld which of the following flaws
would be considered the most serious:
a
b
c
d
5
Depth.
Length.
Width.
Sharpness.
The European Standard for NDE of fusion welds by visual examination is:
a
b
c
d
4
Nick break.
Side bend.
Charpy impact.
Face bend test.
Lack of sidewall fusion.
Slag inclusion.
Linear porosity.
Root concavity.
A fillet weld has an actual throat thickness of 8mm and a leg length of 7mm, what
is the excess weld metal?
a
b
c
d
2.1mm.
1.8mm.
3.1mm.
1.4mm.
WIS10-30816
Appendix 1–Paper 1
A1-1
Copyright © TWI Ltd
7
BS EN ISO 17637 allows the use of a magnifying glass for visual inspection, but
recommends that the magnification is:
a
b
c
d
8
A WPS may specify a maximum width for individual weld beads (weave width)
when welding C-Mn steels. If the width is exceeded it may cause:
a
b
c
d
9
Above the dashed line.
Below the dashed line.
Above the solid line.
Below the solid line.
Which of the following elements is added to steel to give resistance to creep at
elevated service temperatures?
a
b
c
d
13
Prevent linear porosity.
Prevent burn-through.
Prevent oxidation of the root bead.
Eliminate moisture pick-up in the root bead.
According to AWS A2.4 a weld symbol for the other side is placed:
a
b
c
d
12
Tungsten spatter.
Risk of crater cracking.
Risk of arc strikes.
Interpass temperature.
Pipe bores of some materials must be purged with argon before and during TIG
welding to:
a
b
c
d
11
Lack of inter-run fusion.
A reduction in HAZ toughness.
Lack of sidewall fusion.
Too low a deposition rate.
In TIG welding a current slope-out device reduces:
a
b
c
d
10
x2.
x2 to x5.
x5 to x10.
Not greater than x20.
Nickel.
Manganese.
Molybdenum.
Aluminium.
Compound welds:
a Always contain full penetration butt welds.
b Joints which have combinations of welds made by different welding
processes.
c Combinations between two different weld types.
d All of the above.
WIS10-30816
Appendix 1–Paper 1
A1-2
Copyright © TWI Ltd
14
Welding inspectors:
a
b
c
d
15
In an arc welding process, which of the following is the correct term used for the
amount of weld metal deposited per minute?
a
b
c
d
16
The material thickness reduces.
Faster welding speeds.
The use of a larger welding electrode.
A reduction in carbon content in the parent material.
What is the maximum allowable linear misalignment for 8mm material if the code
states the following, ‘Linear misalignment is permissible if the maximum dimension
does not exceed 10% of t up to a maximum of 2mm’?
a
b
c
d
19
27.5mm.
24mm.
13.3mm.
12.5mm.
Pre-heat for steel will increase if:
a
b
c
d
18
Filling rate.
Deposition rate.
Weld deposition.
Weld duty cycle.
The throat thickness of 19mm fillet weld is?
a
b
c
d
17
Normally supervise welders.
Are normally requested to write welding procedures.
Are sometimes requested to qualify welders.
All of the above.
0.8mm.
2mm.
8mm.
None of the above, insufficient information provided.
BS EN ISO 17637:
a The minimum light illumination required for visual inspection is 350 Lux.
b The minimum light illumination required for visual inspection is 500 Lux.
c The minimum light illumination required for visual inspection is 600 Lux at
not less than 30°.
d Doesn’t specify any viewing conditions for visual inspection.
20
Which of the following electrodes and current types may be used for the TIG
welding of nickel and its alloys?
a
b
c
d
Cerium electrode, DC –ve.
Zirconium electrode, AC.
Thorium electrode, DC +ve.
All of the above may be used.
WIS10-30816
Appendix 1–Paper 1
A1-3
Copyright © TWI Ltd
21
When considering the MIG/MAG welding process which of the following metal
transfer modes would be the most suited to the welding of thick plates over 25mm
in PA.
a
b
c
d
22
When considering hydrogen, which of the following welding processes would
produce the lowest levels in the completed weld? (under controlled conditions)
a
b
c
d
23
MMA.
SAW.
TIG.
FCAW.
In steel the element with the greatest effect on hardness is:
a
b
c
d
24
Dip transfer.
Pulse transfer.
Spray transfer.
Globular transfer.
Chromium.
Manganese.
Carbon.
Nickel.
Brittle fractures:
a The susceptibility in steels will increase with the formation of a fine grain
structure.
b The susceptibility in steels will increase with a reduction in the in-service
temperature to sub-zero conditions.
c The susceptibility in steels will increase with a slow cooling rate.
d All of the above.
25
Which of the following steels is considered non-magnetic?
a
b
c
d
26
In a transverse tensile test brittleness would be indicated if:
a
b
c
d
27
18%Cr, 8%Ni.
2.25Cr 1Mo.
9%Cr,1Mo.
9%Ni.
There is a reduction in cross-section at the position of fracture.
The fracture surface is flat and featureless but has a rough surface.
Fracture occurred in the weld metal.
The fracture face shows beach marks.
A STRA test is used to measure the:
a
b
c
d
Tensile strength of the welded joint.
Level of residual stress in butt joints.
Fracture toughness of the HAZ.
Through-thickness ductility of a steel plate (the Z direction).
WIS10-30816
Appendix 1–Paper 1
A1-4
Copyright © TWI Ltd
28
A macrosection is particularly good for showing:
a
b
c
d
29
A suitable gas/gas mixture for GMAW of aluminium is:
a
b
c
d
30
The weld metal HAZ microstructure.
Overlap.
Joint hardness.
Spatter.
100%CO2.
100% Argon.
80% argon + 20% CO2.
98% argon + 2% O2.
A crack running along the centreline of a weld bead could be caused by:
a
b
c
d
Use of damp flux.
Lack of preheat.
Arc voltage too high.
Weld bead too deep and very narrow.
WIS10-30816
Appendix 1–Paper 1
A1-5
Copyright © TWI Ltd
Senior Welding Inspector: Multiple Choice Questions
Paper 2
Name: ……………………………….…………………………. Date: ……………………
1
The maximum hardness in the HAZ of a steel will increase if:
a
b
c
d
2
Initiation of a TIG arc using a high frequency spark may not be allowed because it:
a
b
c
d
3
Often causes tungsten inclusions.
Can damage electronic equipment.
Is an electrical safety hazard.
Often causes stop/start porosity.
In friction welding, the metal at the interface when the joining occurs is described
as being in the:
a
b
c
d
4
Heat input is increased.
CEV is increased.
Joint thickness is decreased.
Basic electrodes are used.
Liquid state.
Intercritical state.
Plastic state.
Elastic state.
What four criteria are necessary to produce hydrogen induced cold cracking?
a Hydrogen, moisture, martensitic grain structure and heat.
b Hydrogen, poor weld profiles, temperatures above 200oC and a slow cooling
rate.
c Hydrogen, a grain structure susceptible to cracking, stress and a temperature
below 300oC.
d Hydrogen, existing weld defects, stress and a grain structure susceptible to
cracking.
5
Austenitic stainless steels are more susceptible to distortion when compared to
ferritic steels this is because:
a
b
c
d
6
High coefficient of thermal expansion, low thermal conductivity.
High coefficient of thermal expansion, high thermal conductivity.
Low coefficient of thermal expansion, high thermal conductivity.
Low coefficient thermal expansion, low thermal conductivity.
Transverse tensile test:
a
b
c
d
Is used to measure the ultimate tensile strength of the joint.
Is used to measure the elongation of a material.
Is used to measure the yield strength of a material.
All of the above.
WIS10-300816
Appendix 1–Paper 2
A1-1
Copyright © TWI Ltd
7
In the welding of austenitic stainless steels, the electrode and plate materials are
often specified to be low carbon content. The reason for this:
a
b
c
d
8
Essential variable:
a
b
c
d
9
Creates problems when welding in position (vertical, horizontal, overhead).
Requires more heat to melt it when compared with aluminium.
Increases weld pool fluidity.
Decreases weld pool fluidity.
A welder qualified in the PG position would normally be qualified for welding:
a
b
c
d
13
Voltage.
Amperage.
Polarity.
Both a and b.
An undesirable property of aluminium oxide residue is that it:
a
b
c
d
12
44%.
144%.
69.4%.
2.27%.
Which of the following will vary the most when varying the arc length using the
MMA welding process?
a
b
c
d
11
In a WPS may change the properties of the weld.
In a WPS may influence the visual acceptance.
In a WPS may require re-approval of a weld procedure.
All of the above.
In an all weld metal tensile test, the original test specimens gauge length is 50mm.
After testing the gauge length increased to 72mm, what is the elongation
percentage?
a
b
c
d
10
To prevent the formation of cracks in the HAZ.
To prevent the formation of chromium carbides.
To prevent cracking in the weld.
Minimise distortion.
All diameters of pipe.
Welding positions PA, PC, PG, and PF.
In position PG only.
All pipe wall thickness.
A fabrication calls for the toes to be blended in by grinding.The most likely reason
for this is to…
a
b
c
d
Make the weld suitable for liquid (dye) penetrant inspection
Improve the fatigue life
reduce residual stresses
improvethe general appearance of the welds
WIS10-300816
Appendix 1–Paper 2
A1-2
Copyright © TWI Ltd
14
A carbon equivalent of 0.48%:
a
b
c
d
15
Is
Is
Is
Is
high for carbon steel and may require a preheat temperature over 100oC.
insignificant for carbon steel and preheat will not be required.
calculated from the heat-input formula.
not a consideration for determining preheating temperatures.
Which of the following statements is true?
a The core wire of an MMA electrode always contains alloying elements.
b Basic electrodes are preferred when welding is carried out in situations where
porosity free welds are specified.
c Rutile electrodes always contain a large proportion of iron powder.
d Cellulose electrodes may deposit in excess of 90ml of hydrogen per 100g of
weld metal.
16
Preheat:
a
b
c
d
17
Which element has the greatest effect on general corrosion resistance?
a
b
c
d
18
2.16 kJ/mm.
0.036 kJ/mm.
2.61 kJ/mm.
0.36 kJ/mm.
Which of the following mechanical test(s) can give a quantitative measurement of
ductility?
a
b
c
d
20
Manganese.
Chromium.
Carbon.
Nickel.
Which of the following is the correct arc energy if the amps are 350, volts 32 and
travel speed 310 mm/minute.
a
b
c
d
19
Must always be carried out on steels.
Need not be carried out if post weld heat is to follow.
Is always carried out using gas flames.
None of the above.
Tensile test.
Bend test
Nick break test.
Both a and b.
Which of the following are applicable to fatigue cracking?
a
b
c
d
A rough randomly torn fracture surface, an initiation point and beach marks.
A smooth fracture surface, an initiation point and beach marks.
Beach marks, step like appearance and a secondary mode of failure.
All of the above.
WIS10-300816
Appendix 1–Paper 2
A1-3
Copyright © TWI Ltd
21
22
Which of the following weld symbols in accordance with BS EN ISO 2553 represents
a fillet weld made on the other side?
a
b
c
d
What is a lap in steel?
a
b
c
d
23
24
A
A
A
A
fold occurring in the steel during forming or rolling.
sub-surface lamination, which may affect the strength of the steel.
type of crack occurring in the parent material.
non-metallic inclusion.
In accordance with BS EN ISO 2553 which of the following symbol best represents
a double J butt weld?
a
b
c
d
Which of the following welding symbols would indicate the depth of penetration in
accordance with BS EN ISO 2553?
a
c
WIS10-300816
Appendix 1–Paper 2
z10
b
s10
d
10s
A1-4
Copyright © TWI Ltd
25
How can you tell the difference between an EN/ISO weld symbol and an AWS weld
symbol?
a The EN/ISO weld symbol will always have the arrow side weld at the top of
the reference line.
b The EN/ISO symbol has the welds elementary symbol placed on the indication
line lying above or below the solid reference line to indicate a weld on the
other side.
c The EN/ISO symbol has a fillet weld leg length identified by the letter ‘a’.
d The EN/ISO symbol has a fillet weld throat thickness identified by the letter
‘z’.
26
What would the number 141 placed at the end of the reference line indicate on a
welding symbol in accordance with BS EN ISO 2553?
a
b
c
d
27
What would the number 136 placed at the end of the reference line indicate on a
welding symbol in accordance with BS EN ISO 2553?
a
b
c
d
28
MMA welding process.
MIG welding process.
FCAW welding process.
MAG welding process.
What is meant by the term normative document?
a
b
c
d
29
NDT requirements.
SAW welding process.
MMA welding process.
TIG welding process.
General term used to cover standards, specifications etc.
A legal document, the requirements of which must be carried out.
A document approved by a recognised body through consensus.
A written description of all essential parameters for a given process.
In the AWS standard for welding symbols which of the following is true.
a The elementary welding symbol is always place below the reference line to
indicate a site weld.
b The elementary welding symbol is always placed above the reference line to
indicate a weld made on the arrow side.
c The elementary welding symbol can be placed above or below the reference
line to indicate a weld made on the other side.
d The elementary welding symbol is always placed below the reference line to
indicate a weld made on the arrow side.
30
Impact test:
a
b
c
d
Is a destructive test used to measure weld zone hardness.
Is a mechanical test used to determine a welds resistance to creep.
Is a dynamic test, which is used to give a measure of notch toughness.
All of the above.
WIS10-300816
Appendix 1–Paper 2
A1-5
Copyright © TWI Ltd
Senior Welding Inspector: Multiple Choice Questions
Paper 3
Name: ……………………………….…………………………. Date: ……………………
1
If arc strikes are found on carbon steel (carbon equivalent of 0.5%), what
undesirable grain structure may be present?
a
b
c
d
2
Which of the following units is used to express the energy absorbed by a charpy
specimen?
a
b
c
d
3
Have
Have
Have
Have
a
a
a
a
lower heat input and a higher degree of grain refinement.
lower heat input and a coarse grain structure.
lower amount of distortion and a higher degree of grain refinement.
higher amount of distortion and a lower degree of grain refinement.
Which of the following would you expect of a martensitic grain structure?
a
b
c
d
6
70 N/mm2 minimum UTS.
70N/mm2 minimum impact strength.
70,000 p.s.i. minimum UTS.
70,000 p.s.i. minimum yield strength.
A multi-run MMA butt weld made on low alloy steel consists of 5 passes using a
6mm diameter electrode, a 12 pass weld made on the same joint using a 4mm
diameter electrode on the same material will:
a
b
c
d
5
Joules.
Newton’s.
Mega Pascal’s.
Both a and c.
What does the 70 represent on an E7010 AWS A5.1 classified electrode?
a
b
c
d
4
Perlite.
Martensite.
Ferrite.
All of the above are undesirable grain structures in constructional steels.
An
An
An
An
increase
increase
increase
increase
in
in
in
in
toughness and a reduction in hardness.
hardness and a reduction in ductility.
ductility and a reduction in toughness.
malleability and an increase in hardness.
Which of the following would reduce the chances of arc blow?
a
b
c
d
A
A
A
A
change
change
change
change
WIS10-30816
Appendix 1–Paper 3
from
from
from
from
AC current to DC current.
DC current to AC current.
DC electrode +ve to DC electrode –ve.
DC electrode –ve to DC electrode +ve.
A1-1
Copyright © TWI Ltd
7
Which of the following mechanical properties of a weld made on C-Mn steel is most
affected if the heat input per unit length is excessively high?
a
b
c
d
8
Which of the following tests would you not expect to be carried out on a welder
qualification test?
a
b
c
d
9
Se 75.
Tm 170.
Yb 169
Co 60.
When carrying out inspection on a Double V butt weld (35° bevel angle), which of
the following NDT methods would be the most suited for the detection of lack of
sidewall fusion in the root region?
a
b
c
d
13
Tesla.
Lux.
Hertz.
Gray.
If it was a requirement to radiograph a 10mm thick steel weldment, which of the
following isotopes would be the most suited with regards to application and
quality?
a
b
c
d
12
Density and contrast.
Sensitivity and definition.
Density and sensitivity.
Contrast and definition.
What are the units used when measuring light intensities for viewing test
specimens using MPI or DPI testing?
a
b
c
d
11
Radiography.
Tensile test.
Macro.
Bend test.
Which two aspects of radiographic images are normally measured?
a
b
c
d
10
Tensile strength.
Ductility.
Toughness.
Elongation.
Ultrasonic Inspection.
Radiographic Inspection.
Magnetic Particle Inspection.
Dye Penetrant Inspection.
Which NDT method would you associate with prods?
a
b
c
d
Radiographic Inspection.
Magnetic Particle Inspection.
Ultrasonic Inspection.
Dye Penetrant Inspection..
WIS10-30816
Appendix 1–Paper 3
A1-2
Copyright © TWI Ltd
14
When conducting DPI, which of the following are critical considerations?
a
b
c
d
15
Which material would be the least effective for DPI?
a
b
c
d
16
It can only be used on material over 3mm thickness.
It can only detect surface defects.
It can only be used on ferrous materials.
Both b and c.
What is the main purpose of an IQI when used in Radiography?
a
b
c
d
20
The same as that required for visual inspection.
350 lux minimum, 500 lux recommended.
500 lux.
Not specified, it’s left to the decision of the NDT technician.
A major disadvantage of MPI is:
a
b
c
d
19
If the component being tested is too large for regular inks to be used.
During the inspection of components underwater.
During the inspection of hot components.
Iron powder is preferred over regular MPI inks due to the higher sensitivity
achieved and ease of application.
During MPI inspection using contrast inks, what is the minimum light intensity
requirements in accordance with the EN standards?
a
b
c
d
18
Carbon Manganese steels.
316L steel.
Cast Iron.
Both a and c.
Why might Iron powder be used when conducting MPI?
a
b
c
d
17
Thickness of component being tested.
Weld preparation details.
Components test temperature.
All of the above.
To
To
To
All
measure defect sensitivity.
assess the smallest defect which can be detected.
measure Radiographic sensitivity.
of the above.
Back step welding is used to reduce:
a
b
c
d
Distortion.
Stress corrosion cracking.
Fatigue failure.
Solidification cracking.
WIS10-30816
Appendix 1–Paper 3
A1-3
Copyright © TWI Ltd
21
Which of the following materials will show the greatest amount of distortion,
assuming heat inputs, material thickness etc. are the same?
a
b
c
d
22
HICC may occur due to which of the following?
a
b
c
d
23
use
use
use
use
of
of
of
of
a large bevel angle.
basic coated electrodes.
small diameter electrodes, maximise the number of weld passes.
large diameter electrodes, minimise the number of weld passes.
Check incoming materials.
Check and monitor consumable handling and storage.
Check calibration certificates.
Measure and monitor residual stress.
The inclusion of the inductance in the welding circuit when using the MIG/MAG
welding process is to:
a
b
c
d
27
The
The
The
The
A duty not normally undertaken by a Senior Welding Inspector:
a
b
c
d
26
The use of E6010 or E6011 electrodes.
Keeping preheat to a minimum.
The maintenance of minimum heat inputs.
None of the above.
Distortion can be reduced by:
a
b
c
d
25
Damp electrodes.
Lack of preheat.
The presence of sulphur.
Both a and b.
The likelihood of hydrogen cracking in a carbon steel weld can be reduced by:
a
b
c
d
24
High tensile strength C/Mn steel.
Mild steel.
316L steel.
QT steel.
Control the rate of spatter in the dip transfer mode.
Control the rate of spatter in the spray transfer mode.
It enables the welder to weld in position at higher current values.
Both a and b.
What is ‘weld decay’?
a A localised reduction in chromium content caused by sulphur and chromium
combining in SS.
b A localised reduction in chromium content caused by iron and chromium
combining in SS.
c A localised reduction in chromium content caused by carbon and chromium
combining in SS.
d A reduction in tensile strength of a material operating at elevated
temperatures under a constant load, which generally leads to a failure of the
component in SS.
WIS10-30816
Appendix 1–Paper 3
A1-4
Copyright © TWI Ltd
28
What are the possible effects of having the heat input too low during welding?
a
b
c
d
29
Which of the following Isotopes may be used for a 25mm thick steel pipe to pipe
weld DWSI (in accordance to BS EN ISO 17636-1)?
a
b
c
d
30
Low toughness, entrapped hydrogen and low hardness.
High hardness, lack of fusion and entrapped hydrogen.
Entrapped hydrogen, low toughness and high ductility.
Lack of fusion, low toughness and a reduction in ductility.
Ir 192.
Co 60.
Se 75.
Yb 169.
During a the welding of a test piece for the purpose of approving a WPS the
following parameters have been recorded: Amps 300, Volts 32, ROL 210mm, time
1 minute. What is the arc energy value?
a
b
c
d
4.1 KJ/mm.
7.38 KJ/mm.
6.4 KJ/mm.
2.74 KJ/mm.
WIS10-30816
Appendix 1–Paper 3
A1-5
Copyright © TWI Ltd
Senior Welding Inspector: Multiple Choice Questions
Paper 4
Name: ……………………………….…………………………. Date: ……………………
Magnetic Particle Testing (MT)
1
Which of the following materials cannot be tested using MT?
a
b
c
d
2
Suspending magnetic particles in a liquid has the advantage of:
a
b
c
d
3
Flaw is at right angles to the direction of the current.
Flaw is parallel to the magnetic flux.
Flaw is at right angles to the magnetic flux.
Current is at right angles to the magnetic flux.
When MPI is performed with fluorescent ink, the maximum level of white light
illumination that must be present at the area under inspection is:
a
b
c
d
6
Iron oxide.
Ferrous sulphate.
Aluminium oxide.
A special high nickel alloy
Maximum sensitivity in MT is achieved when the:
a
b
c
d
5
Making the same amount of detection media go further.
Improving particle mobility.
Preventing corrosion.
Improving contrast.
Magnetic particles for use in magnetic ink are generally made from:
a
b
c
d
4
Cobalt.
Nickel.
Carbon steel.
Brass.
50 lux.
500 lux
2000 microwatts per square millimetre.
20 lux.
Which of the following statements about the use of permanent magnets for MT is
true?
a
b
c
d
They require no power supply.
They are ideal for use with dry magnetic particles.
They provide excellent sensitivity for surface breaking defects.
They give the clearest indications of discontinuities lying parallel to a line
joining the magnet poles.
WIS10-30816
Appendix 1–Paper 4
A1-1
Copyright © TWI Ltd
7
The region in the neighbourhood of a permanent magnet or current carrying device
in which magnetic forces exist is called a:
a
b
c
d
8
The general name given to a simple device used in MPI to indicate field strength
and direction is:
a
b
c
d
9
Flux indicator.
Gauss meter.
Magnetometer.
Dynamometer.
The flash point of a solvent is:
a
b
c
d
10
Magnetic circuit.
Magnetic field.
Leakage field.
Magnetic pole.
The temperature above which there is a danger of spontaneous combustion
of the solvent vapour.
It's boiling point.
The temperature below which there is a danger of spontaneous combustion of
the solvent vapour.
The temperature above which the solvent becomes soluble in water.
The temperature above which a ferromagnetic material becomes nonmagnetic is
called the:
a
b
c
d
Breaking point.
Curie point.
Sharp point.
Turning point.
Penetrant Testing (PT)
11
A disadvantage of penetrant flaw detection is that:
a
b
c
d
12
An advantage of penetrant flaw detection is that:
a
b
c
d
13
It can only detect surface breaking discontinuities.
It cannot be used on fine cracks such as fatigue cracks.
Parts cannot be re-tested.
It cannot be used on non-ferrous materials.
It can be used on non-ferromagnetic materials.
Fluorescent penetrant can be used for on-site testing of large parts.
The temperature of the part need not be considered.
Painted parts can be rapidly tested.
European national codes and standards do not normally permit the penetrant
method to be used outside what temperature range?
a
b
c
d
10-55 C.
15-50 C.
10-50 C.
5-60 C.
WIS10-30816
Appendix 1–Paper 4
A1-2
Copyright © TWI Ltd
14
An advantage of colour contrast penetrants over fluorescent penetrants is that
they:
a
b
c
d
15
Are more sensitive because the indications are easier to see.
Do not require special removers.
Are more suitable for smooth surfaces.
Do not require an electrical power supply.
Typically, when fluorescent penetrants are used:
a The inspector should allow a few minutes before starting inspection to allow
night vision to develop.
b The quantity of white light in the inspection booth should be limited to around
20lux.
c Removal of excess penetrant is monitored under UV-A light.
d All of the above.
16
Which of the following discontinuities would be impossible to detect using the
penetrant method?
a
b
c
d
17
When selecting which penetrant system to employ which of the following factors
must be considered?
a
b
c
d
18
Forging laps.
Grinding cracks.
Non-metallic internal inclusions.
Crater cracks.
Component surface finish.
The sensitivity required.
The compatibility of the penetrant with the material under inspection.
All of the above must be considered.
Which of the following statements concerning liquid penetrant testing is correct?
a Fluorescent penetrants will produce red against white discontinuity
indications.
b Non-fluorescent penetrants require the use of black lights.
c Yellow-green fluorescent indications glow in the dark for easy viewing and
interpretation.
d Fluorescent penetrants produce yellow green visible light under UV-A
illumination.
19
Development time is influenced by the:
a
b
c
d
20
Type of penetrant used.
Type of developer used.
Temperature of the material being tested.
All of the above.
Factors that affect the rate of penetration include:
a
b
c
d
Surface temperature.
Surface condition & cleanliness.
Viscosity.
All of the above.
WIS10-30816
Appendix 1–Paper 4
A1-3
Copyright © TWI Ltd
Ultrasonic Testing (UT)
21
The process of comparing an instrument or device with a standard is called:
a
b
c
d
22
The piezoelectric material in a probe, which vibrates to produce ultrasonic waves, is
called a:
a
b
c
d
23
Water.
Oil.
Gylcerin
Any of the above.
The primary purpose of reference blocks is:
a
b
c
d
27
Filter undesirable reflections from the specimen.
Tune transducer to the correct operating frequency.
Reduce attenuation within the specimen.
Transmit ultrasonic waves from the transducer to the specimen.
A couplant can be:
a
b
c
d
26
Scanning.
Attenuation.
Angulating.
Resonating.
The purpose of a couplant is to:
a
b
c
d
25
Backing material.
Lucite wedge.
Transducer element or crystal.
Couplant.
Moving a probe over a test surface either manually or automatically is referred to
as:
a
b
c
d
24
Angulation.
Calibration.
Attenuation.
Correlation.
To aid the operator in obtaining maximum back reflection.
To obtain the greatest sensitivity possible from an instrument.
To obtain a common reproducible reference standard.
None of the above is correct.
The gradual loss of energy as ultrasonic vibrations travel through a material is
referred to as:
a
b
c
d
Attention.
Attendance.
Attemperation.
Attenuation.
WIS10-30816
Appendix 1–Paper 4
A1-4
Copyright © TWI Ltd
28
Any condition that causes reflection of ultrasound in pulse echo testing can be
referred to as:
a
b
c
d
29
If the cap of a single V (60° included angle) full penetration butt-weld is ground
flush 0 degree compression probe is useful for:
a
b
c
d
30
A dispenser.
A discontinuity.
An attenuator.
A refractor.
Detecting lack of side wall fusion.
Detecting lack of root fusion.
Assessing excess penetration.
All of the above.
Welds in austenitic stainless steel:
a Are easily tested by ultrasonic methods.
b Are difficult to test by ultrasonic methods due to the coarse grain structure of
the weld deposit.
c Are difficult to test by ultrasonic methods due to the highly attenuating
parent material.
d Both b and c are correct.
Radiographic Testing (RT)
31
The two factors that most affect the sensitivity of a radiograph are:
a
b
c
d
32
The instrument used to measure film density is called:
a
b
c
d
33
A
A
A
A
densitometer.
photometer.
radiometer.
proportional counter.
Compared with conventional ultrasonic testing one advantage of film radiography
is:
a
b
c
d
34
Density and unsharpness.
Latitude and grain size.
Density and latitude.
Contrast and definition.
It's cheaper.
A permanent record is directly produced.
Lack of fusion is easily detected.
All of the above are significant advantages.
Which of the following weld defects is most reliably detected by radiography?
a
b
c
d
Porosity.
Lack of inter-run fusion.
Lack of root fusion.
Heat affected zone crack.
WIS10-30816
Appendix 1–Paper 4
A1-5
Copyright © TWI Ltd
35
Which of the following weld defects is least reliably detected by radiography?
a
b
c
d
36
Radiography is a reliable method for the detection of:
a
b
c
d
37
Porosity.
Slag inclusion.
Lack of penetration.
Heat affected zone crack.
Volumetric flaws.
Planar flaws.
Both volumetric and planar flaws.
Laminations in rolled steel products.
DWDI radiography is usually limited to girth welds in pipe with an outside diameter
of (consider EN ISO standard):
a
b
c
d
75mm or less.
80mm or less.
85mm or less.
100mm or less.
38
Radiography is best suited for:
a Cruciform joints.
b Dissimilar welds.
c T butt welds.
d Set through joints
39
The correct terminology for the image that forms on a radiographic film during
exposure to radiation is:
a
b
c
d
40
Ghost image.
Latent image.
Patent image.
Spitting image.
If detected by radiography undercut appears as:
a
A very thin, continuous or intermittent, straight dark line running parallel with
the edge of the weld cap.
b A broad straight edged image towards the centre of the weld image.
c A dark line of variable width, continuous or intermittent, between the weld &
parent material & following the contour of the edge of the weld cap or root.
d A dark irregular image, within the weld image, continuous or intermittent, of
variable width and film density running essentially parallel to the weld axis
WIS10-30816
Appendix 1–Paper 4
A1-6
Copyright © TWI Ltd
Appendix 2
Training Reports
CSWIP 3.2 TRAINING REPORT MT 01
INSPECTION COMPANY: TWI NDT
REPORT NUMBER: 01 PROJECT NUMBER: 1970
CLIENT: Tramcar
WELD NUMBER: 48
SPECIFICATION: TWI NDT specification
WELD DETAILS: Single V butt weld weld number
TECHNIQUE 132/T
SURFACE CONDITION: As welded
PROCEDURE NUMBER: 132
WELDING PROCESS: 111
DATE OF EXAMINATION: 4.8.15
SCOPE OF INSPECTION: 100% of weld and HAZ
LOCATION: Prenton Park workshop
PROCESS STAGE: After PWHT
MATERIAL:ASTM 182
LIFT TEST COMPLETED: YES @ 5.4 KG
CONSUMABLES
MANUFACTURER
TYPE
BATCH NUMBERS
Solvent based ink
Magnaflux
7HF
120514
Contrast Paint
Magnaflux
WCP‐2
150415
Solvent Remover
Magnaflux
SKC‐S
140905
TESTING TECHNIQUE: AC Yoke
TEMPERATURE:Ambient
LIGHT LEVELS: >350Lux at test surface
TEST SENSITIVITY: 3 indications, Burmah castrol strip
CURRENT TYPE: DC
POLE SPACING: 50 mm
TEST RESULTS:
No defects detected
No reportable indications detected
ACTION:
No further actions
OPERATORS NAME: S Jones
REPORT DATE: 4.8.15
OPERATORS SIGNATURE: SJones
OPERATORS QUALIFICATION: CSWIP Level 2 MPI
SJ Training MT01
CSWIP 3.2 TRAINING REPORT PT 01
INSPECTION COMPANY: TWI NDT
REPORT NUMBER: 0011 PROJECT NUMBER: 1970
CLIENT: Tramcar
WELD NUMBER: 69
SPECIFICATION: CSWIP
WELD DETAILS: Single V Butt joint weld
TECHNIQUE 132/PT
SURFACE CONDITION: As welded
PROCEDURE NUMBER: 132
WELDING PROCESS: 141
DATE OF EXAMINATION: 8.4.15
SCOPE OF INSPECTION: 100%
LOCATION: Prenton Park workshop
PROCESS STAGE: Completed
MATERIAL:316 SS
VIEWING CONDITIONS: >500Lux
CONSUMABLES
MANUFACTURER
TYPE
BATCH NUMBERS
Solvent Remover
Magnaflux
7HF
120514
Penetrant
Magnaflux
SKL‐SP2
150415
Developer
Magnaflow
SKC‐S
140905
APPLICATION: Brush
DWELL TIME: 20 minutes
DEVELOPMENT TIME: 10 minutes
TEST TEMPERATURE: 5‐10 oC
TEST RESULTS
ACTIONS
SIGNATURE:
D Pennar
NAME: Dye Pennar
SJ Training PT1
REPORT DATE: 8.4.15
QUALIFICATION: CSWIP LT2 PT (ISO 9712)
CSWIP 3.2 TTRAINING REPORT RT 01
DATE OF INSPECTION: 4.8.15
INSPECTION COMPANY: TWI NDT
REPORT NUMBER: 1970
CLIENT:
WELDING PROCESS: MMA 111
WELD REFERENCE: 47
Tramcar
SURFACE CONDITION: As welded MMA 111
JOINT GEOMETRY
TEST PROCEDURE: 131
STAGE OF TEST: After PWHT
25mm
2.5mm
SCOPE OF INSPECTION: 100%
MATERIAL:
‐ Bevel Angle 30o + 5o, ‐ 0o
‐ Root Gap 2.5mm.
‐ Plate thickness 30 mm
‐Weld Length
C‐Mn
Source Strength: 60 Ci
FFD/SFD: 150 mm
KV's: N/A
mA's: N/A
Screen type: Pb
Exposure: 4Ci mins
Focal Spot:
Source Size: 2x2
FILM TYPE: AGFA D4
IQI TYPE: Fe
DEVELOPMENT: 4 mins @ 20oC manual
FIXING CONDITIONS 6 mins @ 20oC
RADIOGRAPHIC TECHNIQUE: SWSI
ISOTOPE TYPE: Ir 192
TEST RESULTS
FILM ID
SEN %
DENSITY
COMMENTS
ACTION
1‐2
2%
2‐3
No defects observed
Accept
2‐3
2%
2‐3
No defects observed
Accept
3‐4
2%
2‐3
No defects observed
Accept
4‐5
2%
2‐3
No defects observed
Accept
5‐6
2%
2‐3
lack of root penetration
Reject
TEST LIMITATIONS:
TEST OPERATOR: Sjones
SIGNATURE: S Jones
SJ Training RT01
REPORT DATE: 4.8.15
OPERATORS QUALIFICATION: CSWIP L2 RT (EN ISO9712)
CSWIP TRAINING REPORT UT01
INSPECTION COMPANY: TWI NDT
CLIENT: Tramcar
PROJECT NUMBER: 267
REPORT NUMBER:256
PROJECT LOCATION: Prenton Workshop
DATE OF INSPECTION: 4.8.15
JOINT GEOMETRY
SCOPE OF INSPECTION: 100%
WELD NUMBER:24
MATERIAL: Aluminium 5083
DIMENSIONS: 700mm L
FORM:Plate
25mm
SURFACE CONDITION: As welded
2mm
WPS: 0069 GTAW
TEMPERATURE :Ambient
TEST PROCEDURE: 14
− Root Gap 2mm.
− Root to be inspected by MT before commencment
of next weld pass
DETECTION UNIT: KSM
SERIAL NUMBER:6754
COUPLANT: Sonagel
CALIBRATION BLOCKS: V1,V2
SIZE
PROBES
SENSITIVITY
SCANNING
10mm Twin Crystal
BWE 80% F.S.H At test
depth
At test sensitivity
O
10mm Single Crystal
80% F.S.H 1.5mm Hole
At test sensitivity
O
4 MHz 60 Shear
10mm Single Crystal
80% F.S.H 1.5mm Hole
At test sensitivity
O
4 MHz 70 Shear
10mm Single Crystal
80% F.S.H 1.5mm Hole
At test sensitivity
5 MHz 0O Compression
4 MHz 45 Shear
TEST RESULTS: BS EN ISO 17640:2010
1. Crack like indication detected with 60o shear wave scanning in root location.
2. Slag inclusions detected with 45o shear wave scanning
ACCEPTANCE:TWI NDT SPECIFICATION
Not accptabe
NAME:
M Rogers
LEVEL OF QUALIFICATION: CSWIP L2 UT EN ISO 9712
SJ training UT01
SIGNATURE:
REPORT DATE: 4.8.15
Senior Welding Inspector: Training Reports Questions
Name: ……………………………….…………………………. Date: ……………………
MT01 Questions
1
The lift test stated in MT01
a
b
c
d
2
Do you consider the scanning pattern shown to be
a
b
c
d
3
b
c
d
Yes, as so long as you have valid eye test and have completed competency
checks
Yes, it states a minimum of 350 Lux but recommends 500 Lux
No, 350 Lux is for black light not white light
No, 500 Lux is the minimum permitted light intensity
Which of the following statements is correct?
a
b
c
d
5
Correct and fully compliant with the procedure
Missing the dimensions for each span of the yoke conducted
Incorrect and not compliant with the specification
This type of scanning is only applicable to AC
In relation to the light levels reported on MT01, is it stated correctly and which is the
correct statement?
a
4
Is not required if test sensitivity is recorded
Complies with specification and is common practice
Lift testing is for permanent magnets only
Does not comply with the specification
Pole
Pole
Pole
Pole
spacing
spacing
spacing
spacing
is 300mm minimum
is 300mm maximum
is 150mm maximum
depends on the power of the Yoke
Which of the following statements is correct?
a AC Yokes only shall be reported
b DC yokes shall be used in all situations
c According to the TWI specification DC shall be used on raw materials but
not welds
d Permanent magnets shall be used on live plant and AC on non-live plant
WIS10-30816
Appendix 2 – Questions
A2-1
Copyright © TWI Ltd
PT01 Questions
6
In accordance with the TWI specification, at which of the following temperatures is
penetrant inspection permissible
a
b
c
d
7
Do you consider the development time stated in PT01 as
a
b
c
d
8
Acceptable to the TWI specification as no maximum is stated
Not acceptable to the TWI specification
A suitable period as to compliment the dwell time
All options are incorrect
In accordance with the TWI Specification is the material type stated on PT01
acceptable
a
b
c
d
9
Between 1°C and10°C
Between 5°C and 10°C
Between 5°C and 50°C
d. Between 25°C and 40°C
Yes it is acceptable
No, only non-ferrous based materials can be inspected by DPI
It is not specified in the TWI Specification regarding this material so I would
accept
No, Duplex and aluminum are acceptable but the material stated is
unacceptable
In accordance with TWI Specification are the viewing conditions acceptable as stated
in PT01
a
b
c
d
Acceptable if used for the TAM calibration
Yes the conditions are acceptable
No the conditions are not acceptable
Acceptable when doing fluorescent
10 In accordance with the TWI Specification are the consumable manufacturers
acceptable to the TWI specification
a
b
c
d
Yes, they are acceptable
No, they are not acceptable
The developer and penetrant only are acceptable to the specification
The developer and remover only are acceptable to the specification
WIS10-30816
Appendix 2 – Questions
A2-2
Copyright © TWI Ltd
RT01 Questions
11 On Radiographic Inspection report RT 01, is the operator’s qualification acceptable to
the TWI specification?
a
b
c
d
Yes
No
This acceptable if the qualification to ISO 17636 has been verified
This is not acceptable because the level 2 is only a minimum
12 Is the material stated on RT 01?
a
b
c
d
Not permissible in the TWI specification
Not possible to radiograph due to its permeability
Not possible to radiograph due to its high density
Well suited to radiography and is acceptable to the TWI specification
13 Is the scope of inspection reported on RT 01 acceptable to the TWI specification?
a
b
c
d
If that’s all that’s accessible then yes
No
The specification only calls for 10% radiography on project 7690
All options are incorrect
14 In relation to the fixing conditions stated on RT 01
a
b
c
d
The time and temperatures stated are correct
The time is ok but the temperature is too high
The temperature is ok but the time is too long
All options are incorrect
15 In relation to the Development stated on RT 01
a
b
c
d
The time and temperatures stated are correct
The time is ok but the temperature is too low
The temperature is ok but the time is too long
All options are incorrect
WIS10-30816
Appendix 2 – Questions
A2-3
Copyright © TWI Ltd
UT01 Questions
16 Do the calibration blocks shown on UT 01 comply with the requirements of the TWI
specification?
a
b
c
d
The calibration blocks stated are specification compliant
The blocks do not matter providing a resolution check is completed
The calibration blocks stated are not specification compliant
ONLY if a cross checker is present at calibration shall the specification allow
the use of the V1,V2 blocks stated
17 Is it possible to use the 60
reported defect 1?
a
b
c
d
o
shear probe as reported in UT 01 to scan for the
No
Yes
Only the crack like indication ,would be discovered
It is possible if you scan at 40 o to the probe angle itself
18 According to the TWI specification, Is the material stated on report UT 01 acceptable
for ultrasonic examination
a
b
c
d
Yes it is acceptable to the specification with no special requirements.
There is no mention of Aluminum in the specification
Yes, ultrasonic testing is often used on Aluminum welds
If the attenuation check is done then this material can be inspected by UT
with company approval
19 In relation to the joint geometry stated on report UT 01
a
b
c
d
A 6 dB drop should be referenced here
The report should state the bevel angle/included angle
There would be sufficient information to conduct
successfully
A trained operator would know his beam path
ultrasonic
testing
20 How many probes would be used on a 25mm single V butt weld in accordance with
the TWI specification?
a
b
c
d
Only a zero degree would be required for this joint
4 probes would be required
3 probes would be required
All options are feasible if you have access to both sides of the joint
WIS10-30816
Appendix 2 – Questions
A2-4
Copyright © TWI Ltd
Appendix 3
Training Drawing
Drawing one CSWIP 3.2 weld symbols training
Nozzles 50mm dia with 10mm
flanges
Nozzle 450 dia with
20mm flange.
Nozzle 600mm with 40mm
flange.
3
5
4
8
2000mm dia
1
2
7
6
10,000
Appendix 4
Specification Questions
Senior Welding Inspector: Specification Questions
Name: ……………………………….…………………………. Date: ……………………
1.
The symbols s and ≤ refer to :a) Plate thickness and arrow side
b) Nominal throat thickness and less than
c) Nominal butt weld thickness and less than and equal to
d) Single sided and vee butt weld with reinforcement removed
2.
In the case of a ferrous double sided butt weld, which inspection methods should
be employed before the second side is welded.
a) Dye penetrant and MPI
b) Visual only under magnification of x5
c) Visual and dye penetrant
d) Visual and MPI
3.
What would be the largest leg length dimensions and the smallest throat dimension
of a fillet weld deposited on 12mm thick plates.
a) 12mm leg length, 8.4mm throat
b) 15mm leg length, 10.5mm throat
c) 14mm leg length, 9.8mm throat
d) 15mm leg length, 8.4mm throat
4.
An arc strike has been removed by grinding and the inspection has proven
acceptable. The thickness of the joint is 25mm and the removal depth 1mm deep.
Is this acceptable?
a) There is no problem with 1mm as 2mm is acceptable
b) This is not acceptable as no reduction in thickness is allowed
c) Not acceptable as 0.5mm is the maximum reduction in thickness
d) As long as the inspection proved acceptable this would be allowable
5.
Continuous Sub arc welding is being conducted on the manufacture of large I
beams 15m in length. After completion of each I beam, the re cycled flux
approximately 5kg in weight has another 5kg of new flux added before the
operation continues again. Is this allowable?
a) No only new flux can be used
b) This is not required as the system has a filtration system built in
c) This combination of mixing new and used is adequate
d) It depends if the operation is hydrogen controlled or not
WIS10-30816
Appendix 4 – Questions
A4-1
Copyright © TWI Ltd
6.
Ultrasonic testing of a circumferential pipe butt weld 200mm diameter and 25mm
thick, has detected lack of fusion 180mm in length. The contractor has a repair
procedure and wants to carry out a repair. What would be your course of action?
a) If it’s a first repair and the procedure is being followed, this would be allowable
b) If a qualified inspector witnessed the repair this would be allowable
c) You should not allow this to happen until you witness a repeat of the NDT
d) You should insist on a complete cut out
7.
The following parameters were used on a 10mm thick austinetic stainless steel butt
weld using the TIG process, 12 volts, 180 amps and a travel speed of 40mm per
minute. Witnessing this operation, what would be your course of action?
a) The heat input is too high so stop the operation
b) The heat input is too low so stop the operation
c) As long as the welding procedure is adhered to, continue the operation
d) No options are correct
8.
A procedure was conducted in the PF position with MMA in 15mm thick C Mn steel.
The following tests were conducted, hardness, macro, side bends, tensile, and
impacts. Which of the following statements is correct?
a) The procedure can be used in any position
b) The procedure can only be used in the original test position
c) The procedure can be used in the PA, PB, PC and PF positions
d) The procedure can be used in the PC, PF and PD positions
9.
A quenched and tempered steel has to undergo Post Weld Heat Treatment. Which
of the following is correct?
a)
b)
c)
d)
10.
Heating rate controlled from 320°c, soak temperature 590°c,
controlled to 320°c and thermocouples removed at 110°c
Heating rate controlled from 300°c, soak temperature 580°c,
controlled to 300°c and thermocouples removed below 110°c
Heating rate controlled from 220°c, soak temperature 450°c,
controlled to 220°c and removal of thermocouples at this point
Heating rate controlled to
a soak temperature of 700°c,
controlled to ambient at which point thermocouples removed.
cooling rate
cooling rate
cooling rate
cooling rate
A quenched and tempered steel 40mm thick requires pre heating at a temperature
of 100°c and a controlled interpass temperature of 100°c. the SAW process id
being used. The heat input must be controlled. Which of the following conforms?
a)
b)
c)
d)
28
32
32
32
volts,
volts,
volts,
volts,
WIS10-30816
Appendix 4 – Questions
450
650
620
750
amps,
amps,
amps,
amps,
travel
travel
travel
travel
speed
speed
speed
speed
650mm per min
400mm per min
350 mm per min
800 mm per min
A4-2
Copyright © TWI Ltd