QAF011
Rev. 03 Feb. 26, 05
Harvard Technology Middle East
API 570: Piping Inspection Code
Inspection, Repair, Alteration & Rerating of
In-service Piping Systems
(API Exam Preparation Training)
March 5-9, 2005
Abu Dhabi, U.A.E.
Course Instructor(s)
Mr. Ron VanArsdale
This document is the property of the course instructor and/or Harvard Technology Middle East. No part of this document may be
reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying,
recording, or otherwise, without the prior written permission of Harvard Technology Middle East
To The Participant
The Course notes are intended as an aid in following lectures and for review in
conjunction with your own notes; however they are not intended to be a complete
textbook. If you spot any inaccuracy, kindly report it by completing this form and
dispatching it to the following address, so that we can take the necessary action
to rectify the matter.
P. O. Box 26608
Abu Dhabi, U.A.E.
Tel: +971 2 627 7881
Fax: +971 2 627 7883
Email: info@harvard.tc
Name:
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Disclaimer
The information contained in these course notes has been complied
from various sources and is believed to be reliable and to represent
the best current knowledge and opinion relative to the subject.
Harvard Technology offers no warranty, guarantee, or representation
as to it’s absolute correctness or sufficiency.
Harvard Technology has no responsibility in connection therewith; nor
should it be assumed that all acceptable safety and regulatory
measures are contained herein, or that other or additional information
may be required under particular or exceptional circumstances.
**********************************************
Table of Contents
Section 1
API 570
Section 2
API 574
Section 3
ASME B16.5
Section 4
ASME B31.3
Section 5
ASME Section V
Section 6
Welding Processes
Section 7
API 578
Section 8
Welding Terminology
Section 9
Welding Discontinuities
Section 10
ASME Section IX
Section 11
Welding Metallurgy
Section 12
Technical Report Writing
Harvard Technology Middle East
COURSE OVERVIEW IE200
API 570: Piping Inspection Code
Inspection, Repair, Alteration & Rerating of In-service Piping Systems
(API Exam Preparation Training)
Course Title
API 570: Piping Inspection Code: Inspection, Repair, Alteration & Rerating of Inservice Piping Systems (API Exam Preparation Training)
Course Date/Venue
March 05-09, 2005/ Al Hosn Suite, 2nd Floor, Le Royal Meridien, Abu Dhabi, U.A.E.
Course Reference
IE200
Course Duration
5 days (40 hours as per API recommendations)
Course Objectives
In order to meet the needs of today's fast changing inspection industry, Harvard
Technology (ITAC) has developed the "Piping Inspection Course with API 570 Exam
Prep. This comprehensive course is designed to train those individuals who are
interested in obtaining the API 570 Piping Inspection Certification.
Like the API 653 Exam Prep Course, the student receives in-depth instruction
pertaining to passing the API 570 test, as well as insight into the intricacies students
may expect to encounter in the working environment. Harvard Technology (ITAC) is
proud of its 90%+ pass rate, and we hope to include your staff among our
successful candidates. This course is offered as both an in-house and an open
enrollment class. Topics include:
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Introduction
Glossary - Piping Terms
Extensive Discussion of API 570 - Inspection, Repair, Alteration, And Rerating Of InService Piping Systems
Extensive Discussion of ASME B31.3-Chemical Plant and Petroleum Refinery Piping As related to API 570
Overview of
o API 574 - Inspection of Piping, Tubing, Valves and Fittings
o ASME B16.5 - As related to API 570
o ASME Section V - As related to API 570
o ASME Section IX - As related to API 570
o NDT- Basic information
Welding Processes - General Information
Welding Terms - AWS Terminology
Weld Discontinuities - General Information
Summary and Practice Exam
IE200 IE200-03-05
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26 February 2005
Harvard Technology Middle East
Additionally, quizzes are given at the end of each section; homework is handed out
at the end of each class day, which consists of 30 questions per day and is reviewed
at the beginning of the following day, and a “practice” exam is administered at the
end of the course. Harvard Technology (ITAC) is proud of the 90%+ pass rate
attained by its students who have sat for the API 570 certification exam.
Who Should Attend
The course is intended for Inspection Engineers who are seeking API-570
certification. Other engineers, managers or technical staffs who are dealing with
Piping Systems will also benefit.
Course Instructor
Mr. Ron VanArsdale, PE, USA, is the founder of Inspection Training and Consulting
Company (ITAC). His duties include conducting training courses for Harvard
Technology and ITAC, creating new courses for inspection and other related
activities, creating course material, as well as developing custom training programs,
customized written practices and providing trouble-shooting consulting services. In
the past, Mr. VanArsdale was employed by SGS Industrial Services as the
Training Director and the American Welding Society (AWS) as the Curricula
and Course Development Manager. In this position he developed various training
courses dealing with the AWS Certified Welding Inspector program. He planned,
organized, and developed all phases of educational activities for AWS.
In addition to these functions, he is a member of the API 653 Questions
Committee which devised the API 653 Tank Inspector Certification
Examination; as well as a member of the API 570 Questions Committee which is
charged with developing the API 570 Piping Inspector Certification
Examination.
Ron attended San Jacinto College and Texas A&M University, and has a Lifetime
Teaching Certificate from the State of Texas.
He is an AWS Certified Welding Inspector (CWI), ITAC Level III, an API Certified
Aboveground Storage Tank Inspector, and API Certified Piping Inspector, an
AWS Certified Welding Educator (CWE) and is an internationally recognized
Presenter/Instructor. Additionally, he received the AWS Distinguished Member
Award in March, 1989, the AWS CWI of the Year District Award in January,
1993, as well as the AWS District 18 Meritorious Award in September, 1993.
He has thirty-three years experience in the erection, maintenance and inspection
of buildings, petrochemical facilities, vessels, above-ground storage tanks, piping
systems, in addition to teaching welding/inspection education courses.
Mr. VanArsdale is professionally affiliated with the American Welding Society,
American Society for Nondestructive Testing, American Petroleum Institute,
Vocational Industrial Clubs of America, Harvard Technology, American
Inspection Society, the National Job Core and has been appointed a Kentucky
Colonel by the Governor of Kentucky in recognition of his lifetime contribution
to his fellow man.
IE200 IE200-03-05
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26 February 2005
Harvard Technology Middle East
Required Codes & Standards
Listed below are the effective editions of the publications required for the current
Piping Inspector Certification Examination.
Each student must have these
documents available for use during the class.
ƒ A
APPII SSttaannddaarrdd 557700, Piping Inspection Code: Inspection, Repair, Alteration, and Rerating
of In-Service Piping Systems,, Second Edition, October, 1998; including, Addendum 1
(February, 2000) and Addendum 2 (December, 2001) and Addendum 3 (August 2003).
Global Engineering Product Code API CERT 570
ƒ A
APPII R
Reeccoom
mm
meennddeedd PPrraaccttiiccee 557744,, Inspection Practices for Piping System Components,
Second Edition, June 1998. Global Engineering Product Code API CERT 574
ƒ A
APPII R
Reeccoom
mm
meennddeedd PPrraaccttiiccee 557788,, Material Verification Program for New and Existing
Alloy Piping Systems, First Edition, May 1999
ƒ
Global Engineering Product Code API CERT 578
ƒ A
Am
meerriiccaann SSoocciieettyy ooff M
Meecchhaanniiccaall EEnnggiinneeeerrss ((A
ASSM
MEE), Boiler and Pressure Vessel
Code, 2001 edition with 2002 and 2003 addenda.
ƒƒ
i.
A
A
S
M
E
S
o
n
V
AS
SM
ME
ES
Seeeccctttiiio
on
nV
V, Nondestructive Examination, Articles 1, 2, 6, 7, 9, 10 and 23 (Section
SE-797 only).
ii.
S
S
o
n
X
Seeeccctttiiio
on
n IIIX
X, Welding and Brazing Qualifications
A
Am
meerriiccaann SSoocciieettyy ooff M
Meecchhaanniiccaall EEnnggiinneeeerrss ((A
ASSM
MEE))
i.
ii.
B
B
B111666...555, Pipe Flanges and Flanged Fittings, 1996, with 1998 Addenda
B
B
B333111...333, Process Piping, 2002 Edition
Global Engineering Product Code for the ASME package API CERT 570 ASME.
Package includes only the above excerpts necessary for the exam.
API and ASME publications may be ordered through Global Engineering Documents
at 303-397-7956 or 800-854-7179. Product codes are listed above. Orders may also
be
faxed
to
303-397-2740.
More
information
is
available
at
http://www.global.ihs.com. API members are eligible for a 50% discount on all API
documents, exam candidates are eligible for a 20% discount on all API documents.
When calling to order, please identify yourself as an exam candidate and/or API
member. Prices quoted will reflect the applicable discounts. No discounts will be
made for ASME documents.
For the complete sets of ASME documents including future addenda please contact
ASME’s publications department at 1-800-843-2763. In Canada, ASME publications
are available through HIS Canada at 1-800-854-7179 or 613-237-4251
Note: API and ASME publications are copyrighted material. Photocopies of API and
ASME publications are not permitted. CD-ROM versions of the API documents are
issued quarterly by Information Handling Services and are permitted. Be sure to
check your CD-ROM against the editions noted on this sheet.
Course Certificate
Harvard Technology certificate will be issued to all attendees completing minimum of
75% of the total tuition hours of the course.
IE200 IE200-03-05
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26 February 2005
Harvard Technology Middle East
Course Fee
US $ 2,750 per Delegate. This rate includes Participant’s Pack (Folder, Manual,
Hand-outs, etc.), buffet lunch, coffee/tea on arrival, morning & afternoon of each day.
Accommodation
Accommodation is not included in course fees. However, any accommodation
required can be arranged by Harvard Technology at the time of booking.
Course Program
Day 1 : Saturday 05th of March 2005
0730 - 0800
Registration & Coffee
0800 - 0815
Welcome
0815 - 0900
Introduction
0900 - 0930
Students Take Initial Math Quiz
0930 - 1000
Review Math Quiz Answers
1000 - 1015
Break
1015 - 1045
Overview of Course Outline
1045 - 1230
Review of API 570 Body of Knowledge
1230 - 1330
Lunch
1330 - 1430
API 570 - Sections 1 – Scope
1430 - 1500
API 570 - Sections 2 - References
1500 - 1515
Break
1515 - 1545
API 570 - Sections 3 - Definitions
1545 - 1645
API 570 - Sections 4 - Owner/User Inspection Organization
1645 - 1700
Distribute Homework
1700
End of Day One
Day 2 : Sunday 06th of March 2005
0730 - 0830
Review of Day 1 and Homework Answers
0830 - 0930
API 570 - Sections 5 - Inspection And Testing Practices
0930 - 0945
Break
0945 - 1045
API 570 - Sections 6 - Frequency And Extent Of Inspection
1045 - 1130
API 570 - Sections 7 - Inspection Data Evaluation, Analysis, And
Recording
1130 - 1200
API 570 -Sections 8 -Repairs, Alterations & Rerating of Piping Systems
1200 - 1230
API 570 - Sections 9 - Inspection of Buried Piping
1230 - 1330
Lunch
1330 - 1400
API 570 - Appendix A - Inspection Certification
API 570 - Appendix C - Examples of Repairs
API 570 - Appendix D - External Inspection Checklist For Process
Piping
1400 - 1410
Administer API 570 Section Quiz
1410 - 1420
API RP 574 - Section 1 - Scope
1420 - 1430
API RP 574 - Section 3 - Definitions
IE200 IE200-03-05
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Harvard Technology Middle East
1430 - 1440
1440 - 1450
1450 - 1515
1515 - 1530
1530 - 1540
1540 - 1550
1550 - 1600
1600 - 1615
1615 - 1625
1625 - 1635
1635 - 1645
1645 - 1725
1725 - 1730
1730
API RP 574 - Section 4 - Piping Components
API RP 574 - Section 5 - Reasons For Inspection
API RP 574 - Section 6 - Inspecting For Deterioration In Piping
Break
API RP 574 - Section 7 - Frequency And Time Of Inspection
API RP 574 - Section 8 - Safety Precautions And Preparatory Work
API RP 574 - Section 9 - Inspection Tools
API RP 574 - Section 10 - Inspection Procedures
API RP 574 - Section 11 - Determination Of Retirement Thickness
API RP 574 - Section 12 - Records
Administer API 574 Section Quiz
Instruction of ASME B16.5
Distribute Homework
End of Day Two
Day 3 : Monday 07th of March 2005
0730 - 0830
Review of Day 2 and Homework Answers
0830 - 0845
ASME B31.3 - Chapter 1 - Scope And Definitions
0845 - 0910
ASME B31.3 - Chapter 2 (Part 1) - Design Conditions And Criteria
0910 - 0940
ASME B31.3 - Chapter 2 (Part 2) - Pressure Design of Piping
Components
0940 - 1000
ASME B31.3 - Chapter 2 (Part 3) - Fluid Service Requirements For
Piping Components
1000 - 1015
Break
1015 - 1040
ASME B31.3 - Chapter 2 (Part 4) - Fluid Service Requirements For
Piping Joints
1040 - 1100
ASME B31.3 - Chapter 2 (Part 5) - Piping Flexibility
1100 - 1130
ASME B31.3 - Chapter 3 - Materials
1130 - 1230
ASME B31.3 - Chapter 5 - Fabrication, Assembly And Erection
1230 - 1330
Lunch
1330 - 1430
ASME B31.3 - Chapter 6 - Inspection, Examination And Testing
1430 - 1445
Break
1445 - 1630
ASME Section V - Nondestructive Test Methods
1630 - 1645
ASME Section V Quiz
1645 - 1655
Thought Questions
1655 - 1700
Distribute Homework
1700
End of Day Three
Day 4:
Tuesday 08th of March 2005
0730 - 0830
Review of Day 3 and Homework Answers
0830 - 0930
Welding Terms
0930 - 0945
Break
0945 - 1045
Welding Procedures
1045 – 1145
Welding Discontinuities
1145 - 1230
ASME Section IX WPS and PQR
1230 - 1330
Lunch
IE200 IE200-03-05
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26 February 2005
Harvard Technology Middle East
1330 - 1445
1445 - 1500
1500 - 1650
1650 - 1700
1700
Review Procedure Exercise
Break
ASME Section IX - Welder Certification
Distribute Homework
End of Day Four
Day 5: Wednesday 09th of March 2005
0730 - 0830
Review of Day 4 and Homework Answers
0830 - 1000
Question and Answer Session 1
1000 - 1015
Break
1015 - 1230
Question and Answer Session 2
1230 - 1330
Lunch
1330 - 1530
Practice Exam
1530 - 1545
Break
1545 - 1630
Presentation of Certificates
1730
End of course
Course Coordinator
Ms. Rana Tawfiq,
rana@harvard.tc
Tel:
+971-2-6277881,
IE200 IE200-03-05
Page 6 of 6
Rev. 4
Fax:
+971-2-6277883,
Email:
.
26 February 2005
API 570
Piping Inspection Code
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Inspection, Repair, Alteration, and Rerating
Of In-Service Piping Systems
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent API Committee interpretations.
The use of “Key Phrases” is intended as a study
guide only.
Page 1- 1
(This page intentionally left blank)
Page 1- 2
API 570
Second Edition - October, 1998
Addendum 1 - February, 2000
Addendum 2 - December 2001
Inspection, Repair, Alteration, and Rerating
Of In-Service Piping Systems
Foreword
This edition of API 570 supersedes all previous editions of API 570.
Key phrase ”supersedes previous editions...".
1.0
SCOPE
1.1.1
General
API 570 covers inspection, repair, alteration, and rerating procedures
for metallic piping systems that have been in-service.
1.1.2
Intent
Any organization that uses API 570 should maintain or have access to
an authorized inspection agency, a repair organization, qualified
engineers, inspectors and examiners. Key phrase "maintain ...agencies
and qualified technical personnel".
1.1.3
Limitations
Limited to piping that has been placed in-service. Key phrase "placed
in service".
1.2
Specific Applications
Piping systems for process fluids, hydrocarbons, and similar flammable or
toxic fluid services. (Specific services listed in the paragraph.)
Page 1- 3
1.2.1
Included Fluid Services
1.
2.
3.
4.
5.
6.
1.2.2
Raw, intermediate, and finished petroleum products.
Raw, intermediate, and finished chemical products.
Catalyst lines.
Hydrogen, natural gas, fuel gas, and flare systems.
Sour water and hazardous waste streams above threshold limits.
Hazardous chemicals above threshold limits.
Key phrase “Services”.
Excluded and Optional Piping Systems
Piping systems listed here may be excluded from the specific
requirements of API 570, but may be included at the owner's option.
Key phrase "owner's option".
1.3
This edition of API 570 (Second Edition, Addenda 1, Addenda 2 and Addenda
3) recognizes API RP 570 “Fitness For Service.” This Recommended Practice
is not required by API 570, it is simply allowed if the Owner wants to use it.
Key phrase “Fitness For Service”.
2
REFERENCES
3
DEFINITIONS
(For the purposes of this standard, the following definitions apply.)
3.1 alteration: A physical change in
any component that has design
implications affecting the pressure
containing capability or flexibility of a
piping system beyond the scope of its
design. The following are not
considered alterations: comparable or
duplicate replacement, the addition of
any reinforced branch connection
equal to or less than the size of
existing reinforced branch
connections, and the addition of
branch connections not requiring
reinforcement.
3.2 applicable code: The code, code
section, or other recognized and
generally accepted engineering
standard or practice to which the
piping system was built or which is
deemed by the owner or user or the
piping engineer to be most
appropriate for the situation, including
but not limited to the latest edition of
ASME B31.3.
3.3 ASME B31.3: A shortened form of
ASME B31.3, Chemical Plant and
Petroleum Refinery Piping, published by
the American Society of Mechanical
Engineers. ASME B31.3 is written for
design and construction of piping
systems. However, most of the
technical requirements on design,
welding, examination, and materials
also can be applied in the inspection,
rerating, repair, and alteration of
operating piping systems. When
ASME B31.3 cannot be followed
because of its new construction
coverage (such as revised or new
material specifications, inspection
requirements, certain heat treatments,
and pressure tests), the piping
Page 1- 4
engineer or inspector shall be guided
by API 570 in lieu of strict conformity
to ASME B31.3. As an example of
intent, the phrase “principles of ASME
B31.3” has been employed in API 570,
rather than “in accordance with ASME
B31.3”.
3.4 authorized inspection agency:
Defined as any of the following:
a. The inspection organization of the
jurisdiction in which the piping system
is used.
b. The inspection organization of an
insurance company that is licensed or
registered to write insurance for
piping systems.
c. An owner or user of piping systems
who maintains an inspection
organization for activities relating only
to his equipment and not for piping
systems intended for sale or resale.
d. An independent inspection
organization employed by or under
contract to the owner or user of piping
systems that are used only by the
owner or user and not for sale or
resale.
e. An independent inspection
organization licensed or recognized by
the jurisdiction in which the piping
system is used and employed by or
under contract to the owner or user.
3.5 authorized piping inspector: An
employee of an authorized inspection
agency who is qualified and certified
to perform the functions specified in
API 570. A nondestructive
examination (NDE) examiner is not
required to be an authorized piping
inspector. Whenever the term
inspector is used in API 570, it refers to
an authorized piping inspector.
3.6 auxiliary piping: Instrument and
machinery piping, typically small-bore
secondary process piping that can be
isolated from primary piping systems.
Examples include flush lines, seal oil
lines, analyzer lines, balance lines,
buffer gas lines, drains, and vents.
3.7 Critical check valves: Valves that
have been identified as vital to process
safety and must operate reliably in
order to avoid the potential for
hazardous events or substantial
consequences should a leak occur.
3.8 CUI: Corrosion under insulation,
including stress corrosion cracking
under insulation.
3.9 deadlegs: Components of a
piping system that normally have no
significant flow. Examples include the
following: blanked branches, lines
with normally closed block valves,
lines with one end blanked,
pressurized dummy support legs,
stagnant control valve bypass piping,
spare pump piping, level bridles, relief
valve inlet and outlet header piping,
pump trim bypass lines, high-point
vents, sample points, drains, bleeders,
and instrument connections.
3.10 defect: An imperfection of a type
or magnitude exceeding the acceptable
criteria.
3.11 design temperature of a piping
system component: The temperature
at which, under the coincident
pressure, the greatest thickness or
highest component rating is required.
It is the same as the design
temperature defined in ASME B31.3
and other code sections and is subject
to the same rules relating to
allowances for variations of pressure
or temperature or both. Different
components in the same piping
system or circuit may have different
design temperatures. In establishing
the design temperature, consideration
shall be given to process fluid
temperatures, ambient temperatures,
heating and cooling media
temperatures, and insulation.
Page 1- 5
3.12 examiner: A person who assists
the inspector by performing specific
nondestructive examination (NDE) on
piping system components but does
not evaluate the results of those
examinations in accordance with API
570, unless specifically trained and
authorized to do so by the owner or
user. The examiner need not be
qualified in accordance with API 570 or
be an employee of the owner or user
but shall be trained and qualified in the
applicable procedures in which the
examiner is involved. In some cases,
the examiner may be required to hold
other certifications as necessary to
satisfy owner or user requirements.
Examples of other certification that
may be required are American Society
for Non-Destructive Testing SNT-TC1A or CP 189 or American Welding
Society Welding Inspector certification.
The examiner’s employer shall
maintain certification records of the
examiners employed, including dates
and results of personnel qualifications,
and shall make them available to the
inspector.
control chemistry or other process
variables. Injection points control
chemistry or other process variables.
Injection points do not include
locations where two process streams
join (mixing tees). Examples of
injection points include chlorine in
reformers, water injection in overhead
systems, polysulfide injection in
catalytic cracking wet gas, antifoam
injections, inhibitors, and neutralizers.
3.17 in-service: Refers to piping
systems that have been placed in
operation, as opposed to new
construction prior to being placed in
service.
3.18 inspector: An authorized piping
inspector.
3.19 jurisdiction: A legally
constituted government
administration that may adopt rules
relating to piping systems.
3.20 level bridle: A level gauge glass
piping assembly attached to a vessel.
3.14 imperfections: Flaws or other
discontinuities noted during inspection
that may be subject to acceptance
criteria during an engineering and
inspection analysis.
3.21 maximum allowable working
pressure: (MAWP): The maximum
internal pressure permitted in the
piping system for continued operation
at the most severe condition of
coincident internal or external
pressure and temperature (minimum
or maximum) expected during service.
It is the same as the design pressure,
as defined in ASME B31.3 and other
code sections, and is subject to the
same rules relating to allowances for
variations of pressure or temperature
or both.
3.15 indication: A response or
evidence resulting from the
application of a nondestructive
evaluation technique.
3.22 mixing tee: A piping component
that combines two process streams of
differing composition and/or
temperature.
3.16 injection point: Locations where
relatively small quantities of materials
are injected into process streams to
3.23 MT: Magnetic-particle testing.
3.13 hold point: A point in the repair
or alteration process beyond which
work may not proceed until the
required inspection has been
performed and documented.
Page 1- 6
3.24 NDE: Nondestructive
examination.
3.25 NPS: Nominal pipe size
(followed, when appropriate, by the
specific size designation number
without an inch symbol).
3.26 on-stream: Piping containing any
amount of process fluid.
3.27 owner/user: An owner or user of
piping systems who exercises control
over the operation, engineering,
inspection, repair, alteration, testing,
and rerating of those piping systems.
3.28 owner/user inspector: An
Authorized Inspector employed by an
Owner-User who has qualified either
by written examination under the
provisions of Section 4 and Appendix
A of API 570 or has qualified under the
provisions of A.2, and who meets the
requirements of the jurisdiction.
3.29 PT: A liquid-penetrant testing.
3.30 pipe: A pressure-tight cylinder
used to convey a fluid or to transmit a
fluid pressure and is ordinarily
designated “pipe” in applicable
material specifications. (Materials
designated “tube” or “tubing” in the
specifications are treated as pipe when
intended for pressure service.)
3.31 piping circuit: A section of
piping that has all points exposed to an
environment of similar corrosivity and
that is of similar design conditions and
construction material. Complex
process units or piping systems are
divided into piping circuits to manage
the necessary inspections, calculations,
and record keeping. When
establishing the boundary of a
particular piping circuit, the inspector
may also size it to provide a practical
package for record keeping and
performing field inspection.
3.32 piping engineer: One or more
persons or organizations acceptable to
the owner or user who are
knowledgeable and experienced in the
engineering disciplines associated with
evaluating mechanical and material
characteristics affecting the integrity
and reliability of piping components
and systems. The piping engineer, by
consulting with appropriate specialists,
should be regarded as a composite of
all entities necessary to properly
address a technical requirement.
3.33 piping system: An assembly of
interconnected piping that is subject to
the same set or sets of design
conditions and is used to convey,
distribute, mix, separate, discharge,
meter, control, or snub fluid flows.
Piping system also includes pipesupporting elements but does not
include support structures, such as
structural frames and foundations.
3.34 primary process piping: Process
piping in normal, active service that
cannot be valved off or, if it were
valved off, would significantly affect
unit operability. Primary process
piping normally includes all process
piping greater than NPS 2.
3.35 PWHT: Postweld heat treatment.
3.36 renewal: Activity that discards
an existing component and replaces it
with new or existing spare materials of
the same or better qualities as the
original component.
3.37 repair: The work necessary to
restore a piping system to a condition
suitable for safe operation at the
design conditions. If any of the
restorative changes result in a change
of design temperature or pressure, the
requirements for rerating also shall be
satisfied. Any welding, cutting, or
grinding operation on a pressurecontaining piping component not
Page 1- 7
specifically considered an alteration is
considered a repair.
3.38 repair organization: Any of the
following:
a. An owner or user of piping systems
who repairs or alters his or her own
equipment in accordance with API 570.
b. A contractor whose qualifications
are acceptable to the owner or user of
piping systems and who makes
repairs or alterations in accordance
with API 570.
c. One who is authorized by,
acceptable to, or otherwise not
prohibited by the jurisdiction and who
makes repairs in accordance with API
570.
3.39 rerating: A change in either or
both the design temperature or the
maximum allowable working pressure
of a piping system. A rerating may
consist of an increase, a decrease, or a
combination of both. Derating below
original design conditions is a means
to provide increased corrosion
allowance.
3.40 secondary process piping: Smallbore (less than or equal to NPS 2)
process piping downstream of
normally closed block valves.
3.41 small-bore piping (SBP): Piping
that is less than or equal to NPS 2.
3.42 soil-to-air (S/A) interface: An
area in which external corrosion will
vary depending on factors such as
moisture, oxygen content of the soil,
and operating temperature. The zone
generally is considered to be from 12
inches (305 millimeters) below to 6
inches (150 millimeters) above the soil
surface. Pipe running parallel with the
soil surface that contacts the soil is
included.
3.43 spool: A section of piping
encompassed by flanges or other
connecting fittings such as unions.
3.44 temper embrittlement: A loss of
ductility and notch toughness in
susceptible low-alloy steels, such as 1
1/4 Cr and 2 1/4 Cr, due to prolonged
exposure to high-temperature service
[7000 F to 10700 F (3700 C to 5750 C)].
3.45 temporary repairs: Repairs made
to piping systems in order to restore
sufficient integrity to continue safe
operation until permanent repairs can
be scheduled and accomplished within
a time period acceptable to the
inspector or piping engineer.
3.46 test point: An area defined by a
circle having a diameter not greater
than 2 inches (50 millimeters), or a line
diameter not exceeding 10 inches (254
millimeters), or not greater than 3
inches (76 millimeters) for larger lines.
Thickness readings may be averaged
within this area. A test point shall be
within a thickness measurement
location.
3.47 thickness measurement locations
(TMLs): Designated areas on piping
systems where periodic inspections
and thickness measurements are
conducted.
3.48 WFMT: Wet fluorescent
magnetic-particle testing.
3.49 alloy material: Any metallic
material (including welding filler
materials) that contains alloying
elements, such as chromium, nickel or
molybdenum, which are intentionally
added to enhance mechanical or
physical properties and/or corrosion
resistance.
3.50 material verification program: A
documented quality assurance
procedure used to assess metallic alloy
materials (including weldments and
Page 1- 8
attachments where specified) to verify
conformance with the selected or
specified alloy material designated by
the owner/user. This program may
include a description of methods for
alloy material testing, physical
component marking and program
record-keeping.
3.51 positive material identification
(PMI) testing: Any physical
evaluation or test of a material to
conform that the material which has
been or will be placed into service is
consistent with the selected or
specified alloy material designated by
the owner/user. These evaluations or
tests may provide qualitative or
quantitative information that is
sufficient to verify the nominal alloy
composition.
3.52 fitness-for-service assessment: A
methodology whereby flaws and
conditions contained within a structure
are assessed in order to determine the
integrity of the structure for continued
service.
3.53 industry-qualified UT shear
wave examiner: A person who
possesses an ultrasonic shear wave
qualification from API or an
equivalent qualification approved by
the owner/user.
3.54 off-site piping: Piping systems
not included within the plot (battery)
Limits of a process unit, such as a
hydrocracker, an ethylene cracker or a
crude unit. Examples of off-site piping
include tank farm piping and other
lower consequence piping outside the
limits of the process unit.
3.55 on-site piping: Piping systems
included within the plot limits of
process units, such as, a hydrocracker,
an ethylene cracker, or a crude unit.
Page 1- 9
4
OWNER/USER INSPECTION ORGANIZATION
4.1
General
This section establishes an inspection organization to control inspection
programs of piping. Key phrase “inspection”.
4.2
Authorized Piping Inspector Qualification
Requirements for becoming an "Authorized piping inspector."
The term inspector as used by API 570 refers to an authorized piping
inspector. See Appendix B for certification requirements. Key phrase
“Authorized Piping Inspector”.
4.3
Responsibilities
The owner-user shall have overall responsibility for compliance with API 570.
The piping engineer is responsible to the owner-user. The repair
organization shall be responsible to the owner-user.
Key phrase “owner/user”.
5
INSPECTION AND TESTING PRACTICES
5.1
Risk-Based Inspection
The paragraph contains a few general statements about an RBI program.
This paragraph neither requires or prevents inspection based on RBI. Key
phrase "Risk-Based Inspection".
5.2
Preparation
This section covers the preparation usually done before the piping inspection
begins, such as, permits to enter the area, reviewing history of the system,
etc. Key phrase "preparation".
Page 1- 10
5.3
Inspection for Specific Types of Corrosion and Cracking
Areas that should be inspected for possible problems are listed, see API
Recommended Practice 571 for additional information.
The areas of deterioration are:
•
•
•
•
•
•
•
•
•
•
•
•
5.3.1
Injection points
Deadlegs
Corrosion under insulation (CUI)
Soil-to-air (S/A) interfaces
Service specific and localized corrosion
Erosion and corrosion/erosion
Environmental cracking
Corrosion beneath linings and deposits
Fatigue cracking
Creep cracking
Brittle fracture
Freeze damage
Key phrase “deterioration”.
Injection Points
Often subject to accelerated or localized corrosion, more than under
normal conditions. Suggestions for establishing injections point circuit,
for inspection circuits:
•
•
Upstream
12 inches or three pipe diameters upstream whichever is
greater.
•
Downstream
The second change in flow direction or 25 feet downstream,
beyond the first flow change whichever is less.
Injection nozzles
12 inches upstream of the nozzle and continuing for at least ten pipe
diameters downstream of the injection point.
TMLs (thickness measurement locations)
a. Establish TMLs on fittings
b. Establish TMLs on the pipe wall
c. Establish TMLs on longer straight piping
d. Establish TMLs on both upstream and downstream limits of
injection points circuit.
The preferred methods of inspection of injection points are
radiography and/or ultrasonics. These methods are used to
established thickness, not weld quality. Key phrase “injection points”.
Page 1- 11
5.3.2 Deadlegs
Due to the corrosion rate variation both the active and stagnant end of
a deadleg should be inspected. Consideration should be given to
removing the deadlegs that serve no useful purpose. Key phrase
“deadlegs”.
5.3.3 Corrosion Under Insulation (CUI)
External corrosion of an insulated piping system. The corrosion is
usually from trapped moisture that may include rain, water leaks,
condensation, and deluge systems. The most common form of CIU is
localized corrosion of carbon steel and chloride stress corrosion
cracking of austenitic stainless steels. Key phrase “CUI”.
5.3.3.1 Insulated Piping Systems Susceptible to CUI
a.
b.
c.
d.
e.
Areas exposed to overspray from cooling water towers
Areas exposed to steam vents
Areas exposed to deluge systems
Areas subject to process spills, moisture, or acid vapors
Carbon steel piping systems operating between 25oF and
250oF
f. Carbon steel piping systems above 250oF in intermittent
service
g. Deadlegs and attachments protruding from insulated
systems that may operate at a different temperature than
the active line
h. Austenitic stainless steel piping systems operating between
150oF and 400oF
i. Vibrating piping systems
j. Steam traced piping systems
k. Piping systems with deteriorated coatings and/or
wrappings
Key phrase “CUI”
5.3.3.2 Common Locations on Piping Systems Susceptible to CUI
a.
b.
c.
d.
e.
f.
g.
h.
i.
All damaged insulation.
Termination of insulation.
Missing insulation.
Poorly installed insulation.
Termination of insulation on vertical piping.
Caulking problems.
Bulges in insulation, could be an indication of CUI.
Low points.
Carbon or low-alloy steel flanges, bolting etc., especially if in
a high-alloy system.
j. Areas where insulation plugs have been removed and not
properly sealed.
Key phrase “CUI”.
Page 1- 12
5.3.4 Soil-to-Air Interface
Soil-to-air (S/A) interfaces without cathodic protection shall be
included in scheduled external piping inspections. Special interest in
this area, note also concrete-to-air and asphalt-to-air have special
requirements. Caulking in these areas are often a main concern.
Key phrase “S/A”.
5.3.5
Service-specific and Localized Corrosion
The three elements of an inspection program:
•
•
•
An inspector with knowledge of the service and where corrosion is
likely to occur.
Extensive use of NDE.
Communication from operations when process upsets occur that
may affect corrosion rates.
Examples of service-specific corrosion are listed in the rest of the
paragraph. Key phrase “Inspection Program”.
5.3.6 Erosion and Corrosion/Erosion
Erosion can be defined as the removal of surface material by the action
of numerous individual impacts of solid or liquid particles. Erosion
usually occurs in areas of turbulent flow. Inspect the following for
erosion/corrosion:
a. Downstream of control valves.
b. Downstream of orifices.
c. Downstream of pump discharges.
d. Flow direction change.
e. Downstream of piping configurations that produce turbulence.
Key phrase “erosion and corrosion”.
5.3.7 Environmental Cracking
The topics mentioned here are SCC (Stress Corrosion Cracking) and
HIC (Hydrogen Induced Cracking) these types of cracking are results
of specific services reacting with the basic metallurgy of the piping. If
this type of cracking is found in pressure vessels, then the related
piping may have the same problem. Key phrase “cracking”.
5.3.8 Corrosion Beneath Linings and Deposits
Usually it is not necessary to remove the linings, internal or external, if
there is no evidence of damage. However, if deposits, such as coke,
are present, it is important to determine if any active corrosion is
beneath the deposits. Key phrase “corrosion”.
Page 1- 13
5.3.9 Fatigue Cracking
Fatigue cracking is cracking that usually results from cyclic stresses. A
piping system may be designed below the static yield strength of the
material, but due to the number of heat-up high cycles changing to
cool-down low cycles the material may fail. This problem may be
detected by PT, MT or (AE) acoustic emission. Key phrase “fatigue
cracking”.
5.3.10 Creep Cracking
Creep is dependent on time, temperature, and stress. One of the most
common examples of creep cracking has been experienced in the
industry is in 1 1/4 Cr steels above 9000 F. Creep cracking NDE include
PT, MT, UT, RT, and in-situ metallography. Under special conditions
AE may be employed. Key phrase “creep cracking”.
5.3.11 Brittle Fracture
Failure of piping at lower temperatures, usually below 600 F. Most
incidences have occurred during a hydrotest or other over load
condition. Special attention should be used when rehydrotesting lowalloy steels (especially 2 1/4 Cr-1 Mo material), because of temper
embrittlement, also to ferritic stainless steels. (See API RP 579, Sec. 3).
Key phrase “brittle fracture”.
5.3.12 Freeze Damage
Inspections should be performed after subfreezing temperatures.
Water and aqueous solutions in piping systems may freeze and cause
failure because of expansion. Leaks may not be evident until the
system thaws. Key phrase “freeze damage”.
5.4
Types of Inspection and Surveillance
The basic types of inspection include:
• Internal visual inspection.
• Thickness measurement inspection.
• External visual inspection.
• Vibrating piping inspection.
• Supplemental inspection.
Key phrase “inspection”.
5.4.1
Internal Visual Inspection
This type of inspection is not normally performed on piping systems,
unless there is large diameter piping involved. Key phrase “internal
inspection”.
Page 1- 14
5.4.2
Thickness Measurement Inspection
Thickness measurements are used for internal condition and
remaining thickness of piping systems. Measurements may be taken
by inspectors or examiners. Key phrase “thickness measurements”.
5.4.3
External Visual Inspection
Items to inspect are listed in this section. Inspections may be
performed by inspectors, qualified operating or maintenance
personnel. The operating or maintenance personnel shall be qualified
through an appropriate amount of training. Key phrase “external
visual inspection”.
5.4.4
Vibrating Piping and Line Movement Surveillance
This inspection should be performed at junctions where vibrating
piping systems are restrained. Key phrase “vibrating”.
5.4.5
Supplemental Inspection
Profile radiography, thermography, acoustic emission, acoustic leak
detection and ultrasonics can be used where appropriate.
5.5
Thickness Measurement Locations
5.5.1
General
TMLs thickness measurement locations are specific areas along the
piping circuit where inspections are to be made. This section outlines
general TML monitoring and selection. Extremely basic. Key phrase
“TML”.
5.5.2 TML Monitoring
TMLs should be monitored based on the corrosiveness of the system.
Thickness measurements should include measurements at each of the
four quadrants on pipe and fittings, with special attention to the inside
and outside radius of elbows and tees. Key phrase “TML”.
5.5.3
TML Selection
Basic broad rules for TML selection are found in this section, the
information found here is extremely basic. Key phrase “TML”.
5.6
Thickness Measurement Methods
Piping larger than 1” NPS (Nominal Pipe Size) ultrasonic thickness measuring
instruments are accurate. The radiographic profile techniques are preferred
for pipe 1” NPS and smaller. When piping temperatures are above 1500 F, a
special procedure and equipment must be used. Typical problems when
using UT digital instruments are discussed. Key phrase “UT Thickness”.
Page 1- 15
5.7
Pressure Testing of Piping Systems
Pressure testing is not normally conducted as part of a routine inspection.
When this test is used, it should be performed in accordance with ASME
B31.3. Piping of 300 series stainless steel should by hydrotested with potable
water or steam condensate. A pneumatic pressure test may be used when it
is impracticable to hydrotest the system. Such tests must be in compliance
with ASME B31.3. Precautions should be used when safety relief valves are
installed in the system. Isolation or removal of the safety relief valves may
be necessary during the test. Key phrase “pressure test”.
5.8
Material Verification and Traceability
This section was updated in the first addenda to specify “alloy material.” All
materials, except pure iron, more commonly called “pig iron” are made by
using alloying agents. This section also mentions the new API RP 578,
Material Verification Program for new an existing alloy piping system.”
This testing can be performed by the inspector OR the examiner. Remember,
the owner/user will decide on when to use a “PMI (Positive Material
Identification) testing program.” Key phrase “alloy material” and “PMI”.
5.9
Inspection of Valves
Refer to API Standard 598 for closure pressure tests. Other inspections
include external visual examinations, as well as internal inspections if metal
loss is suspected. Key phrase “valves”.
5.10
Inspection of Welds In-Service
The use of profile radiography is recommended when searching for
corrosion or other imperfections in welds that are in-service. Weld
imperfections may be the result of original weld fabrication or service. A
determination should be made as to what caused the problem. This may be
evaluated by:
• Inspector judgment.
• Certified welding inspector judgment.
• Piping engineer judgment.
• Engineering fitness-for-service analysis.
The following should be considered when assessing the quality of existing
welds:
1. Original fabrication inspection acceptance criteria.
2. Extent, magnitude, and orientation of imperfections.
3. Length of time in-service.
4. Operating versus design conditions.
5. Presence of secondary piping stresses.
6. Potential for fatigue loads.
7. Potential for environmental cracking.
8. Weld hardness.
Page 1- 16
Note: Some welds may meet original construction criteria but will not
perform satisfactorily in-service. In addition to radiography, UT shear wave
examination is now allowed. Fitness-for-service monitoring is one
application. Key phrase “welds in-service”.
5.11
Inspection of Flanged Joints
Check the gaskets and bolting. If the flanges have been clamped and
pumped with sealant, check for additional leakage. See API Recommended
Practice 574 for procedures when flanges are opened. Key phrase “flanges”.
6
FREQUENCY AND EXTENT OF INSPECTION
6.1
General
This extremely general section discusses the RBI concept used to establish a
piping circuit inspection strategy. Inspection may be based on the expected
forms of degradation, the optimal inspection frequency, extent of inspection
and the prevention and mitigation steps to reduce the likelihood and
consequence. Key phrase “RBI”.
6.2
Piping Service Classes
This section suggests piping be categorized into different classes, or hazard
levels, using API Recommended Practice 750 and NFPA (National Fire
Prevention Association) 704 as guidelines. Key phrase “service classes”.
6.2.1
Class 1
Class 1 piping is piping whose services have the highest potential of
resulting in an immediate emergency if a leak were to occur. Class 1
piping include, but not limited to, the following:
1. Flammable services that may auto-refrigerate and lead to brittle
fracture.
2. Pressurized services that may rapidly vaporize during release,
creating vapors that may collect and form an explosive mixture,
such as C2 (ethylenes), C3 (propylenes), C4 (butanes) streams.
Fluids that will rapidly va0orize are those with atmospheric boiling
temperatures below 50oF.
3. Hydrogen sulfide (greater than 3 percent weight) in a gaseous
stream.
4. Anhydrous hydrogen chloride.
5. Hydrofluoric acid.
6. Piping over or adjacent to water and piping over public
throughways.
Key phrase “emergency”.
Page 1- 17
6.2.2 Class 2
Class 2 piping is usually unit process piping and selected off-site piping
that is not included in Class 1 piping. Examples are as follows:
1. On-site hydrocarbons that will slowly vaporize during release such
as those operating below the flash point.
2. Hydrogen, fuel gas, and natural gas.
3. On-site strong acids and caustics.
Key phrase “process piping”.
6.2.3
Class 3
Class 3 piping contains services that are flammable but do not
significantly vaporize and are not located in high-activity areas.
Examples are:
1. On-site hydrocarbons that will not significantly vaporize during
release such as those operating below the flash point.
2. Distillate and product lines to and from storage and loading.
3. Off-site acids and caustics.
Key phrase “Class 3”.
6.3
Inspection Intervals
The criteria for inspection intervals are as follows:
1.
2.
3.
4.
Corrosion rate and remaining life calculations.
Piping services classification.
Applicable jurisdictional requirements.
Judgment of the inspector, piping engineer, engineer supervisor, or a
corrosion specialist, based on operating conditions, history, current results
and special conditions.
The owner-user shall establish inspection intervals for thickness
measurements and external visual inspections. Refer to Table 6-1 (page 6-3)
for recommended inspection intervals. Inspections should be based on Table
6-1 or half the remaining life determined from the corrosion rates which ever
is shorter. Key phrase “inspection interval”.
6.4
Extent of Visual External and CUI Inspections
External inspections should be scheduled in accordance with Table 6-1 (page
6-3) using the checklist in Appendix D, EXTERNAL INSPECTION
CHECKLIST FOR PROCESS PIPING Alternatively, API RP 580, an RBI
system can be used.
See Table 6-2 - Recommended Extent of CUI Inspection Following Visual
Inspection. Key phrase “visual external inspections”.
Page 1- 18
6.5
Extent of Thickness Measurement Inspection
As a minimum, a representative sampling of TMLs shall be measured,
including various types of components and orientations in each circuit.
See 3.2.1 for inspection of injection points. Key phrase “TML”.
6.6
Extent of Small-Bore, Auxiliary Piping, and ThreadedConnections Inspections
6.6.1 Small-Bore Piping Inspection
Small-bore piping (SBP) that is primary process piping should be
inspected in accordance with all the requirements of API 570.
Key phrase “SBP”.
6.6.2
Auxiliary Piping Inspection
Inspection of auxiliary SBP is optional, dependent on classification,
cracking potential, corrosion, and potential for CUI.
Page 1- 19
7
INSPECTION DATA EVALUATION, ANALYSIS AND RECORDING
7.1.1
Remaining Life Calculations
Remaining life (years)=
t actual - t required
-----------------corrosion rate
[inches (millimeters) per year]
Where:
t actual = the actual minimum thickness, in inches (millimeters),
determined at the time of inspection.
t required = the required thickness, in inches (millimeters), for the
limiting section or zone.
The long term (L. T.) corrosion rate:
Corrosion rate (L. T.) = t initial - t actual
--------------time (years) between initial
and actual inspections
The short term (S. T.) corrosion rate:
Corrosion rate (S. T.) = t previous - t actual
--------------time (years) between previous
and actual inspections
Long Term and Short Term rates should be compared to see which
results in the shortest remaining life as part of the data assessment.
Key phrase “corrosion rate”.
7.1.2 Newly Installed Piping Systems or Changes in Service
Probable corrosion rates may be determined by use of the following:
1. Corrosion rate of similar service.
2. Owner user’s experience or published data on comparable service.
3. Initial thickness shall be made after 3 months of service by using
NDT.
Key phrase “corrosion rate”.
7.1.3
Existing Piping Systems
Corrosion rates shall be calculated on either a short-term basis, using
the two most recent inspections or long-term basis, using original wall
thickness and most recent inspection, use the higher result in most
cases. Key phrase “corrosion rate”.
Page 1- 20
7.2
Maximum Allowable Working Pressure Determination
The maximum allowable working pressure (MAWP) for the continued use of
piping systems shall be established using the applicable code. Computations
may be made if all the following comply with the applicable code:
1.
2.
3.
4.
5.
Upper and/or lower temperature limits for specific materials.
Quality of materials and workmanship.
Inspection requirements.
Reinforcement of openings.
Any cyclical service requirements.
See Table 7-1
API 570 uses the “Half-Life” concept
Key phrase “MPWA”.
7.3
Minimum Required Thickness Determination
The minimum required pipe wall thickness shall be based on pressure,
mechanical, and structural considerations using the appropriate design
formulae and code allowable stress. Key phrase “minimum thickness”.
7.4
Assessment of Inspection Findings
Fitness-for-service techniques may be evaluated by API 579.
Key phrase “fitness-for-service assessment”.
7.5
Piping Stress Analysis
Piping must be supported and guided so that:
1. its weight is carried safely;
2. it has sufficient flexibility for thermal expansion or contraction;
3. it does not vibrate excessively.
Key phrase “stress analysis”.
7.6
Reporting and Records for Piping System Inspection
API 574 offers guidance for piping inspection records. Key phrase “records”.
Page 1- 21
8
REPAIRS, ALTERATIONS, AND RERATING OF PIPING SYSTEMS
8.1
Repairs and Alterations
The principles of ASME B31.3 or the code to which the piping system was
built shall be followed for repairs and alterations. Key phrase “ASME B 31.3”.
8.1.3
Welding Repairs (Including on-stream)
8.1.3.1 Temporary Repairs
Temporary repairs may be used, full encirclement welded split
sleeve or box-type enclosure. Split coupling or plate patch may
also be used. Temporary repairs should be removed and
replaced at the next available maintenance opportunity.
Key phrase “temporary repairs”.
8.1.3.2 Permanent Repairs
Replacement pipe may be installed or insert patches (flush
patches) may be used if:
1. Full-penetration groove welds are provided.
2. For Class 1 and Class 2 piping systems, the welds shall be
100% radiographed or ultrasonically tested.
3. Patches may be any shape but shall have rounded corners.
Key phrase “permanent repairs”.
8.1.4 Nonwelding Repairs (on-stream)
Temporary repairs may be made by installing a bolted leak clamp.
Pumping of such clamps is allowed. All temporary repairs shall be
removed and appropriate actions taken to restore the original
integrity of the system. Key phrase “nonweld repairs”.
8.2.1
Procedures, Qualifications, and Records
Procedures and welders shall be qualified in accordance with ASME
B31.3 or the code to which the piping was built. Key phrase “ASME
B31.3
8.2.2
Preheating and Postweld Heat Treatment
Preheating shall be in accordance with the applicable code and
qualified welding procedure, exceptions must be approved by the
piping engineer. Preheating may not be considered as an
alternative to environmental cracking prevention.
• Postweld Heat Treatment (PWHT) should be in compliance with
ASME B31.3 or the code to which the piping was built. Local PWHT
may be substituted for 360-degree banding on local repairs.
Key phrase “preheating and PWHT”.
•
Page 1- 22
8.2.3
Designs
Butt joints shall be full-penetration groove welds. Fillet welded
patches are allowed if approved by the piping engineer. Key phrase
“patches”.
8.2.6
Pressure Testing
Pressure testing after repairs or alterations may be employed.
Nondestructive examination (NDE) shall be utilized in lieu of a
pressure test. Key phrase “pressure test”.
8.3
Rerating
Rerating piping systems by changing the temperature rating or MAWP may
be done only if:
1. Calculations are performed by the piping engineer or the inspector.
2. All reratings shall be in accordance with the requirements of code to
which the system was built, newest edition.
3. Current records verify the system is satisfactory and corrosion allowance
is provided.
4. Rerated piping systems shall be leak tested.
5. All pressure relieving devices are checked and appropriately set.
6. The piping system rerating is acceptable to the inspector or piping
engineer.
7. All piping components are adequate for the new pressure and
temperature.
8. Piping flexibility is adequate for design temperature changes.
9. Engineering records are updated.
10. A decrease in minimum operation temperature is justified by impact test
results.
Key phrase “rerating”.
Page 1- 23
9
INSPECTION OF BURIED PIPING
9.1
Types and Methods of Inspection
•
•
•
•
•
Above-grade visual surveillance
Close-interval potential survey
Pipe coating holiday survey
Soil resistivity
Cathodic protection monitoring
Inspection Methods
1. Intelligent pigging
2. Video cameras
3. Excavation
Key phrase “buried piping”.
9.2
Frequency and Extent of Inspection
1. The owner-user should, at approximately 6-month intervals, survey the
surface conditions on and adjacent to each pipeline path.
2. 5-year intervals for poorly coated pipes with little or no cathodic
protection.
3. 5-year intervals for piping not cathodically protected.
4. Piping systems cathodically protected see Section 10 of NACE RP0169 or
Section 9 of API RP 651.
5. External and internal inspection intervals see Table 9-1 - Frequency of
Inspection for Buried Piping Without Effective Cathodic Protection.
Key phrase “buried piping”.
9.2.7 Leak Testing Intervals
The leak testing procedure of buried piping systems has been changed,
the new procedure calls for an 8 hour test as opposed to the old
requirement for 12 hours, repressurization is now to be done at 4
hours after initial pressurization, the 5 percent drop in pressure is still
acceptable. Key phrase “pressure test”.
9.3
Repairs to Buried Piping Systems
Repairs to coatings, any coating removed for inspection shall be renewed and
inspected.
Key phrase “buried piping”.
Page 1- 24
APPENDIX A - INSPECTOR CERTIFICATION
This Appendix covers the examination, grading, and validation of the API 570 exam.
Certification and recertification guidelines are also found in this section.
Addenda 3 now requires re-testing of each inspector after six years, or during the
second renewal. The details have not yet been released.
APPENDIX B - TECHNICAL INQUIRIES
This is an avenue to allow communications from interested parties and the API 570
Committee.
APPENDIX C - EXAMPLES OF REPAIRS
D-1 Repairs
See figure D-1 Encirclement Repair Sleeve and Figure D-2 Small Repair
Patches.
APPENDIX D - EXTERNAL INSPECTION CHECKLIST
FOR PROCESS PIPING
See page D - 1 for the short external inspection checklist for process piping.
Page 1- 25
ITAC
Visit our website: www.itac.net
Inspection Training And Consulting
Post Office Box 5666
Pasadena, TX 77508-5666
Phone (281) 998-8305
Fax (281) 998-2163
API 570
Quiz
1. API 570 covers inspection of:
A.
B.
C.
D.
new construction
new tank construction
in-service piping
in-service vessels
2. CUI is the acronym for:
A.
B.
C.
D.
Corrosion Under Insulation
Cold Under-ground In-service piping
Corrosion Under Inside flow
Carpet Under Infra-structure
3. A person who assists the inspector by performing specific NDE on piping
systems is termed:
A.
B.
C.
D.
NDE technician
Inspector assistant
Level II inspector
Examiner
4. The response or evidence resulting from the application of a nondestructive
evaluation technique is termed:
A.
B.
C.
D.
A crack
Porosity
A leak
An indication
5. The MAWP is:
A.
B.
C.
D.
The maximum internal pressure permitted in the piping system.
The minimum internal pressure permitted in the piping system.
The maximum external pressure permitted in the piping system.
The maximum external stress permitted in the piping system.
Page 1- 26
6. A section of piping encompassed by flanges or other connecting fittings is
called:
A.
B.
C.
D.
A flanged pipe
A ready to be installed pipe
A spooled piece
A fabricated piping assembly
7. If a person has a degree in engineering he is automatically qualified to be:
A.
B.
C.
D.
An Authorized Piping Inspector
A piping inspector
A NDE Level II or III in any technique
None of the above
8. A TML is:
A.
B.
C.
D.
Thickness Material Laboratory
Taiwan Made Label
Thickness Measurement Location
Time Medium Length
9. The result of excessive cyclic stresses that are often well below the static yield
strength of the material is titled:
A.
B.
C.
D.
material failure
fatigue cracking
failure cracking
creep cracking
10. Thickness measurements may be taken by ultrasonic instruments or what
other method:
A. AET
B. ET
C. MT
D. RT
11. Which of the following tests are not normally conducted as part of a routine
inspection:
A.
B.
C.
D.
UT Thickness
Visual Inspection
Radiographic profile
Pressure tests
Page 1- 27
12. Thickness measurements are not routinely taken on ______ in piping
circuits.
A.
B.
C.
D.
valves
straight run pipe
fittings
deadlegs
13. During the installation of a flanged connection, the bolts should:
A.
B.
C.
D.
Extend two threads past their nuts.
Extend completely through their nuts.
Extend only half way through their nuts.
Extend at least .5 inches (1.25 mm) past their nuts.
14. Services with the highest potential of resulting in an immediate emergency
if a leak were to occur are in:
A.
B.
C.
D.
Class 3
Class 2
Class 1
Owner/user designated system
15. The classification that includes the majority of unit process piping is labeled:
A.
B.
C.
D.
Class 3
Class 2
Class 1
Owner/user designated system
16. Services that are flammable but do not significantly vaporize when they leak
and are not located in high activity areas:
A.
B.
C.
D.
Class 3
Class 2
Class 1
Owner/user designated system
17. What is the remaining life in years of a piping systems whose corrosion rate
is .074 inches per year, the actual wall thickness is .370 inches and the
minimum required thickness is .1 inches?
A. 36.48 years
B. 364.8 years
C. 3.6 years
D 3.6 months
Page 1- 28
18. What is the long term corrosion rate of a piping circuit that started at .375 inches
and is now .1 inch, the measurements were taken over a five year period.
A.
B.
C.
D.
.055 inches per year
.005 inches per year
.550 inches per year
Not enough information given
19. What is the short term corrosion rate of the above piping circuit.
A.
B.
C.
D.
.055 inches per year
.005 inches per year
.550 inches per year
Not enough information given
20. A longitudinal crack in an existing piping circuit may be repaired by:
A.
B.
C.
D.
installing a full encirclement welded split sleeve
welding over the crack
welding a box over the cracked area
using a full encirclement welded split sleeve, with the approval of the
piping engineer
Page 1- 29
API 570 Quiz
Answer Key
1. C
2. A
3. D
4. D
5. A
6. C
7. D
8. C
9. B
10. D
11. D
12. A
13. B
14. C
15. B
16. A
Paragraph 1.1.1
Paragraph 3.8
Paragraph 3.12
Paragraph 3.15
Paragraph 3.21
Paragraph 3.43
Paragraph A.2.1
Paragraph 3.47
Paragraph 5.3.9
Paragraph 5.6
Paragraph 5.7
Paragraph 5.9
Paragraph 5.11
Paragraph 6.2.1
Paragraph 6.2.2
Paragraph 6.2.3
18. A
Paragraph 7.1.1
17. C
Paragraph 7.1.1
Remaining life (years)=
t actual - t required
-----------------corrosion rate
[inches (millimeters) per year]
Where:
t actual = the actual minimum thickness, in
inches (millimeters), determined at the
time of inspection.
t required = the required thickness, in
inches (millimeters), for the limiting
section or zone.
The long term (L. T.) corrosion rate:
Corrosion rate (L. T.) = t initial - t actual
--------------time (years) between initial
and actual inspections
19. A
Paragraph 7.1.1
The short term (S. T.) corrosion rate:
Corrosion rate (S. T.) = t previous - t actual
--------------time (years) between previous
and actual inspections
20. D
Paragraph 8.1.3.1
Page 1- 30
API 574
Inspection Practices for
Piping System Components
API Recommended Practice 574
Second Edition, June 1998
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent API Committee interpretations.
The use of “Key Phrases” is intended as a study
guide only.
Page 2 - 1
Inspection Practices for
Piping System Components
API Recommended Practice 574
Second Edition, June 1998
Foreword
This recommended practice is based on the accumulated knowledge and
experience of engineers and other personnel in the petroleum industry. Key
phrase “recommended practice".
1
SCOPE
API 574 covers the inspection practices for piping, tubing, valves (other than
control valves), and fittings used in petroleum refineries and chemical plants.
2
REFERENCES
3
DEFINITIONS
3.1
ASME B31.3: Abbreviation for
ASME/ANSI B31.3, Process Piping,
published by the American Society of
Mechanical Engineers. ASME B31.3 is
written for design and construction of
piping systems. However, most of the
technical requirements on design,
welding, examination, and materials
also can be applied in the inspection,
rerating, repair, and alteration of
operating piping systems. When
ASME B31.3 cannot be followed
because of its new construction
coverage, such as revised or new
material specifications, inspection
requirements, certain heat treatments,
and pressure tests, the piping
engineer/inspector shall be guided by
API 570 in lieu of strict conformance
with ASME B31.3. As an example of
intent, the term “principles” of ASME
B 31.3 has been employed in API 570
rather than the phrase “in accordance
with” ASME B31.3.
3.2
CUI: Corrosion under
insulation, which includes stress
corrosion cracking under insulation.
3.3
deadlegs: Components of a
piping system that normally have no
significant flow. Examples include
blanked branches, lines with normally
closed block valves, lines which have
one end blanked, pressurized dummy
support legs, stagnate control valve
bypass piping, spare pump piping,
level bridles, relief valve inlet and
outlet header piping, pump trim
bypass lines, high point vents, sample
points, drains, bleeders, and
instrument connections.
Page 2 - 2
(This page intentionally left blank)
Page 2 - 3
3.4
defect: In NDE usage, a defect
is an imperfection of a type or
magnitude exceeding the acceptable
criteria.
3.5
design temperature: The
temperature at which, under the
coincident pressure, the greatest
thickness or highest rating of a piping
system component is required. It is
equivalent to the design temperature,
as defined in ASME B31.3 and other
code sections, and is subject to the
same rules relating to allowances for
variations of pressure or temperature
or both. Different components in the
same piping system or circuit may
have different design temperatures.
In establishing this temperature,
consideration shall be given to process
fluid temperatures, ambient
temperatures, heating/cooling media
temperatures, and insulation.
3.6
imperfection: Flaws or other
discontinuities noted during inspection
that may be subject to acceptance
criteria on engineering/inspection
analysis.
3.7
injection points:
Locations
where relatively small quantities of
materials are injected into process
streams to control chemistry or other
process variables. Injection points do
not include the locations where two
process streams join (mixing tees).
Examples of injection points include
chlorine in reformers, water injection
in overhead systems, polysulfide
injection in catalytic cracking wet gas,
anti-foam injections, inhibitors, and
neutralizers.
3.8
in-service: Refers to piping
systems that have been placed in
operation as opposed to new
construction prior to being placed in
service.
3.9
inspector: An authorized
piping inspector.
3.10 jurisdiction: A legally
constituted government
administration that may adopt rules
relating to piping systems.
3.11 mixing tees: A component that
combines two process streams of
differing composition and/or
temperature.
3.12 NDE: Nondestructive
examination.
3.13 NPS: Nominal pipe size
(followed, when appropriate, by the
specific size designation number
without an inch symbol).
3.14 on-stream: Piping containing
any amount of process fluid.
3.15 owner-user: An operator of
piping systems who exercises control
over the operation, engineering,
inspection, repair, alteration, testing,
and rerating of those piping systems.
3.16
PT: Liquid penetrant testing.
3.17 pipe: A pressure-tight cylinder
used to convey a fluid or to transmit a
fluid pressure, ordinarily designated
“pipe” in applicable material
specifications. (Materials designated
“tube” or “tubing” in the specifications
are treated as pipe when intended for
pressure service.)
3.18 piping circuit: Complex
process units or piping systems are
divided into piping circuits to manage
the necessary inspections, calculations,
and record keeping. A piping circuit is
a section of piping of which all points
are exposed to an environment of
similar corrosivity and which is of
similar design conditions and
construction material. When
establishing the boundary of a
particular piping circuit, the Inspector
may also size it to provide a practical
package for record-keeping and
performing field inspection.
Page 2 - 4
3.19 piping engineer: One or more
persons or organizations acceptable to
the owner-user who are
knowledgeable and experienced in the
engineering disciplines associated with
evaluating mechanical and material
characteristics which affect the
integrity and reliability of piping
components and systems. The piping
engineer, by consulting with
appropriate specialists, should be
regarded as a composite of all entities
necessary to properly address a
technical requirement.
3.20 piping system: An assembly of
interconnected piping, subject to the
same set or sets of design conditions,
used to convey, distribute, mix,
separate, discharge, meter, control, or
snub fluid flows. Piping system also
includes pipe-supporting elements, but
does not include support structures,
such as building frames, bents, and
foundations.
3.21 PWHT: Post weld heat
treatment.
maximum allowable working pressure
of a piping system. A rerating may
consist of an increase, decrease, or a
combination. Derating below original
design conditions is a means to
provide increased corrosion
allowance.
3.24 small bore piping (SBP): Less
than or equal to NPS 2.
3.25 soil-to-air (S/A) interface: An
area in which external corrosion may
occur on partially buried pipe. The
zone of the corrosion will vary
depending on factors such as
moisture, oxygen content of the soil,
and the operating temperature. The
zone generally is considered to be
from 12 inches (30 cm) below to 6
inches (15 cm) above the soil surface.
Pipe running parallel with the soil
surface that contacts the soil is
included.
3.26 spools: A section of piping
encompassed by flanges or other
connecting fittings, such as unions.
3.22 repair: A repair is the work
necessary to restore a piping system
to a condition suitable for safe
operation at the design conditions. If
any of the restorative changes result in
a change of design temperature or
pressure, the requirements for
rerating also shall be satisfied. Any
welding, cutting, or grinding
operation on a pressure-containing
piping component not specifically
considered an alteration is considered
a repair.
3.27 temper embrittlement: A loss of
ductility and notch toughness in
susceptible low-alloy steels (e.g., 1 1/4
Cr and 2 1/4 Cr) due to prolonged
exposure to high temperature service
(between 7000 to 1070 F (3710 C to
5770 C)).
3.23 rerating: A change in either or
both the design temperature or the
3.29 WFMT or WFMPT: Wet
fluorescent magnetic particle testing.
3.28 thickness measurement
locations (TMLs): Designated areas
on piping systems where periodic
inspections and thickness
measurements are conducted.
Page 2 - 5
4
PIPING COMPONENTS
4.1
Piping
Piping can be made from any material that can be rolled and welded, cast, or
drawn through dies to form a tubular section. The difference from traditional
thickness designations and schedules is indicated. Small bore piping (NPS 2
pipe size and less) is also included. See Table 1 for nominal sizes. Key phrase
“piping”.
4.2
Tubing
Tubing is generally seamlessly drawn. General information about tubing.
Key phrase “tubing”.
4.3
Valves
The basic types of valves are gate, globe, plug, ball, diaphragm, butterfly,
check, and slide valves. See Figures 1 - 8 for cross section view of each of
theses valves. All of Section 4.3 is general basic information about valves.
Key phrase “valves”.
4.4
Fittings
Fittings are used to connect pipe sections and change the direction of flow or
allow the flow in a piping run to be diverted or added to. The basic types of
pipe fittings, cast, forged, seamlessly drawn, or formed and welded. Fittings
may be flanged, socketwelded, butt welded or threaded. . See Figures 9 - 16
for cross section view of each of theses fittings. All of Section 4.4 and 4.5 is
general basic information about pipe fittings. Key phrase “fittings”.
5
REASONS FOR INSPECTION
5.1
General
The primary purpose of inspection is to achieve the desired quality assurance
and ensure plant safety and reliability. Key phrase "inspection".
5.2
Safety
Basic information about common sense piping safety. Key phrase “safety”.
5.3
Reliability and Efficient Operation
An added benefit to having a regular inspection program, is that it creates a
data bank of information regarding the physical condition of equipment and
the rate and causes of deterioration. The user can then establish effective
preventative maintenance schedules. This effort should result in reduced
maintenance costs and more reliable and efficient operations.
Page 2 - 6
5.4
Regulatory Requirements
Federal, state, and local statutes and regulations may apply to piping
installation and inspection. Key phrase “regulatory requirements”.
6
INSPETING FOR DETERIORATION IN PIPING
Aboveground piping is subject to atmospheric corrosion; buried piping is
subject to soil corrosion. See Figures 17, 18, 19, 20 and 23 for illustrations of
corrosion and eroding of piping.”
6.1
General
Petro-chemical piping, by nature, often carries highly corrosive materials, it is
suggested API IRE Chapter II, Conditions Causing Deterioration or Failures, be
reviewed for causes of deterioration.
Key phrase “deterioration”.
6.2
Corrosion Monitoring Of Process Piping
The most frequent reason for replacing piping is from thinning due to
corrosion. A good monitoring system is imperative. Things to consider
when establishing a corrosion-monitoring plan:
a. Classifying the piping accordance with API 570.
b. Categorizing the piping into circuits of similar corrosion behavior.
c. Identifying susceptible locations where accelerated corrosion is expected.
d. Accessibility of the TML’s for monitoring.
Key phrase “corrosion monitoring”.
6.2.1
Piping Circuits
The basic factors of pipe wall corrosion are listed. As well as,
suggestions for breaking piping systems into circuits, see figure 21 for
an example. Key phrase “piping circuits”.
6.2.3
Piping Classifications
Factors to consider when classifying piping are, toxicity, volatility,
combustibility, location of the piping with respect to personnel and
other equipment, and experience and history. Key phrase
“classifications”.
Page 2 - 7
6.3
Inspection For Specific Types Of Corrosion And Cracking
General information about the following subjects are found in the rest of this
section:
a.
Injection points.
b.
Deadlegs.
c.
Corrosion under insulation (CUI).
d.
Soil-to-air interfaces.
e.
Service specific and localized corrosion.
f.
Erosion and corrosion/erosion.
g.
Environmental cracking.
h.
Corrosion beneath linings and deposits.
i.
Fatigue cracking.
j.
Creep cracking.
k.
Brittle fracture.
l.
Freeze damage.
m.
Corrosion at support points.
n.
Dew Point Corrosion.
7
FREQUENCY AND TIME OF INSPECTION
7.1
General
The frequency and time of inspection should be determined by the
following conditions:
• a. The severity of service.
• b. The degree of risk.
• c. The amount of corrosion allowance remaining.
• d. The historical data available.
• e. Regulatory requirements.
Key phrase “frequency and time”.
7.2
Inspection While Equipment Is Operating
Many other conditions in piping systems should be determined while the
equipment is operating. On-stream inspection can reduce downtime by the
following means:
a. Extending process runs and preventing some unscheduled shutdowns.
b. Permitting fabrication of replacement piping before a shutdown.
c. Eliminating unnecessary work and reducing personnel requirements.
d. Aiding maintenance planning to reduce surges in work load.
Key phrase “On-stream inspection”.
7.3
Inspection While Equipment Is Shut Down
Piping can often be inspected internally during outages.
Key phrase “equipment shut down”.
Page 2 - 8
8
SAFETY PRECAUTIONS AND PREPARATORY WORK
8.1
Safety Precautions
This section outlines some generic, extremely basic safety precautions which
are probably inferior to your own safety department requirements. Key
phrase “safety”.
8.2
Preparatory Work
This section should be titled:
“The Common Sense Guide to Advance Shut Down Work”. It contains no new or
extremely useful information. Key phrase “preparatory work”.
9
INSPECTION TOOLS
See Table 2, page 30 of API 570.
10
INSPECTION PROCEDURES
10.1
Inspection While Equipment Is Operating
10.1.1 Visual Inspection
10.1.1.1 Leaks
Leaks can be safety or fire hazards, and always result in
economic loss. Temporary or permanent repairs can often be
made while the lines are in service. Key phrase “leaks”.
10.1.1.2 Misalignment
Piping should be inspected for misalignment. Pipe dislodged
from supports, vessel wall deformation, pipe supports out of
plumb, excessive replacement of bearings, etc., shifting of
baseplates, foundation damage, cracks in connecting flanges,
expansion joints not performing properly, are all indications of
misalignment. Key phrase “misalignment”.
10.1.1.3 Supports
Supports are shoes, hangers, and braces, and should be visually
inspected for problems. Key phrase “supports”.
Page 2 - 9
10.1.1.4 Vibration
Vibrating or swaying piping should be inspected for cracks, at
points of restraint, usually in the areas of anchors, or where
small bore pipe is attached to the main line. Key phrase
“vibration”.
10.1.1.5 External Corrosion
Defects in the protective coatings and insulation will permit
moisture to contact the piping. This can result in corrosion and
metal loss. Key phrase “external corrosion”.
10.1.1.6 Accumulations of Corrosive Liquids
Some liquids are corrosive to steel piping, spills should be
cleaned up or neutralized. Key phrase “accumulations of
corrosive liquids”.
10.1.1.7 Hot Spots
Operating piping at higher than design limits may cause
bulging, even to the point of failure. Investigation of these
areas is essential. Key phrase “hot spot”.
10.1.2 Thickness Measurements
10.1.2.1 Ultrasonic Inspection
UT digital thickness gauges are mentioned with emphasis on
high temperature readings. Key phrase “UT thickness”.
10.1.2.2 Radiographic Inspection
Wall shot or radiographic profile radiography is discussed in
this section, as to the use of the technique, no information about
how the technique is performed. Key phrase “radiography”.
10.1.3 Other On-stream Inspections
This section mentions “new” methods of inspection; halogen leak
detectors, magnetic induction, real-time radiography, neutron
radiography, thermography, etc. Key phrase “methods”.
10.2
Inspection While Equipment Is Shut Down
10.2.1 Visual Inspection
10.2.1.1
Corrosion, Erosion, and Fouling
Borescopes are used to inspect piping internally. Key phrase
“internal inspection”.
Page 2 - 10
10.2.1.2 Cracks
Inspect the susceptible locations, construction tack welds at
other than pressure welds, heat affected areas joining welds,
and points of restraint or excessive strain. Include locations that
are subject to stress-corrosion cracking, hydrogen cracking, and
caustic or amine embrittlement, as well as exposed threads. Key
phrase “cracks”.
10.2.1.3 Gasket Faces of Flanges
General inspection. Key phrase “flanges”.
10.2.1.4 Valves
Inspection techniques for gate valves including the valves being
dismantled at specified intervals. Key phrase “valves”.
10.2.1.5 Joints, 10.2.1.5.1 Flanged Joints, 10.2.1.5.2 Welded Joints,
10.2.1.5.3 Threaded Joints, 10.2.1.5.4 Clamped Joints
All the listed joints should be inspected, the basic technique is
visual examination. Key phrase “joints”.
10.2.1.6 Misalignment
Misalignment is caused by:
a. Inadequate provision for expansion.
b. Broken or defective anchors or guides.
c. Excessive friction on sliding saddles, indicating a lack
of lubrication or a need for rollers.
d. Broken rollers or rollers that cannot turn because of
corrosion or lack of lubrication.
e. Broken or improperly adjusted hangers.
f. Hangers that are too short and thus limit movement
or cause lifting of the pipe.
g. Excessive operating temperature.
Key phrase “misalignment”.
10.2.1.7 Vibration
Vibrating or swaying piping should be inspected for cracks, at
points of restraint, usually in the areas of anchors, or where
small bore pipe is attached to the main line. Key phrase
“vibration”.
10.2.1.8 Hot Spots
A short discussion of areas over heated on piping is discussed.
No mention of thermal photography. Key phrase “hot spots”.
Page 2 - 11
10.2.2 Thickness Measurements
UT digital thickness gauges are mentioned with emphasis on high
temperature readings and the use of radiography on nipple thickness.
Key phrase “thickness measurement”.
10.2.3 Pressure Tests
Pressure tests are leak tests and may be used on the following:
a. Underground lines and other inaccessible piping.
b. Water and other non-hazardous utility lines.
c. Long oil transfer lines in areas where a leak or spill would not
be
hazardous to personnel or harmful to the environment.
d. Complicated manifold systems.
e. Small piping and tubing systems.
f. All systems, after a chemical cleaning operation.
Do not over pressure the system!
Various fluids may be used for pressure testing:
a. Water with or without an inhibitor, freezing-point
depressant, or wetting agent.
b. Liquid products normally carried in the system, if non-toxic
or flammable.
c. Steam
d. Air, carbon dioxide, nitrogen, helium, or another inert gas.
Salt water can create problems like pitting and corrosion.
Pneumatic tests should be conducted strictly in accordance with
ASME B 31.3. Key phrase “pressure test”.
10.2.4 Hammer Testing
Hammer testing is an old method of testing piping systems, do not use
the hammer on cast iron and stress-relieved lines in caustic and
corrosive service. Key phrase “hammer test”.
10.2.5 Inspection of Piping Welds
Refer to API 570, Section 3.10 which will reference ASME B 31.3 for
weld quality. Key phrase “weld quality”.
10.3
Inspection Of Underground Piping
Basic information about buried piping, referencing several NACE documents.
10.3.1 Types and Methods of Inspection and Testing
10.3.1.1 Above-Grade Visual Surveillance
Extremely basic information about leaking underground piping.
Key phrase “leaks”.
Page 2 - 12
10.3.1.2 Close-Interval Potential Survey
This type of survey is used to locate corrosion cells, galvanic
anodes, stray currents, coating problems, underground
contacts, areas of low pipe-to-soil potentials and other cathodic
protection problems. Key phrase “Close-interval potential
survey”.
10.3.1.3 Holiday Pipe Coating Survey
Basically, a measurement is taken and compared to other areas
of the system, coated as opposed to noncoated piping will give
different corrosion rates and readings. Key phrase “holiday
pipe coating survey”.
10.3.1.4 Soil Resistivity Testing
The Wenner method, the soil bar and soil box methods are
discussed. Basically, each method measures a voltage drop,
caused by a known current flow, across a measured volume of
soil. The resistance factor is used in a formula to determine the
resistivity of the soil. Key phrase “soil resistivity testing”.
10.3.1.5 Cathodic Protection Monitoring
Refer to NACE RP0169 and Section 11 of API Recommended
Practice 651. Key phrase “CP monitoring”.
Sections 10.3.2 Inspection Methods, 10.3.21. Intelligent Pigging, 10.3.2.2 Video
Cameras, 10.3.2.3 Excavation are all basic with little or no useful information.
10.3.3 Leak Testing
The basic methods of leak testing underground piping are briefly
described in this section. The methods are:
a.
Pressure decay method.
b.
Volume in/volume out method.
c.
Single-point volumetric methods.
d.
A marker chemical (tracer) method.
e.
Acoustic emission method.
10.4
Inspection Of New Construction
10.4.1 General
Must meet the requirements of ASME B 31.3. Key phrase “ASME B
31.3”.
Page 2 - 13
10.4.2 Inspection of Materials
Materials should be checked for conformance with the codes and
specifications that are appropriate for the plant. Checks should be
made using material test kits or a nuclear alloy analyzer, (PMI)). Key
phrase “ASME B 31.3”.
10.4.3 Deviations
No comment.
11
DETERMINATION OF RETIREMENT THICKNESS
11.1
Piping
All formulas and data for determining the required wall thickness for piping
are found in ASME B 31.3. ASME B 31.3 also takes into consideration the
following:
a. Corrosion.
b. Threads.
c. Stresses caused by mechanical loading, hydraulic surge pressure,
thermal expansion, and other conditions.
The Barlow formula:
The Barlow formula can be used provided that the value is less than D/6, or
P/SE is not greater than 0.385”. The Barlow formula is as follows:
t = PD/2SE
Where:
t = pressure design thickness for internal pressure, in inches
P = Internal design gauge pressure of the pipe, in pounds
per square inch
D = outside diameter of the pipe, in inches
S = allowable unit stress at the design temperature, in pounds
per square inch
E = longitudinal joint efficiency.
Metallic pipe for which t > D/6 or P/SE > 0.385 requires special
consideration. Key phrase “Barlow formula”.
NOTE: The Barlow formula has been omitted from B31.3, 2000 addenda. The
remaining formulas give practically the same answer.
11.2
Valves And Flanged Fittings
Refer to ASME B16.34 for minimum valve wall thickness. Key phrase “ASME
B 31.3”.
Page 2 - 14
12
RECORDS
12.1
General
Records should be kept in a detailed and orderly manner. These records will
help in evaluating replacement or repair intervals. Key phrase “records”.
12.2
Sketches
Sketches have important functions:
a. They identify particular piping systems in terms of location, size,
material specification, general process flow, and service conditions.
b. They inform the mechanical department of points to be opened for
visual inspection and parts that require replacement or repair.
c. They serve as field data sheets on which can be recorded the
locations of thickness measurements, serious corrosion, and sections
requiring immediate replacement. These data can be transferred to
continuous records at a later date.
d. They assist at future inspections in determining locations that
urgently require examination.
Key phrase “sketches”.
12.3
Numbering Systems
Use any convenient means. Key phrase “numbering systems”.
12.4
Thickness Data
A record of thickness data may provide a means of corrosion or erosion rates
for the piping system. See Figure 25 for an example of sketches and thickness
data. Key phrase “thickness data”.
12.5
Review Of Records
General information about when to review records. Key phrase “records”.
Page 2 - 15
API 574
Quiz
1. API 574 covers inspection of:
A.
B.
C.
D.
new construction
new tank construction
piping
vessels
2. Cast iron pipe can be joined by:
A.
B.
C.
D.
welding
compression
epoxy resin
bell and spigot
3. The primary purpose of inspection is to achieve the desired quality
assurance and:
A.
B.
C.
D.
ensure plant safety
supply the necessary paperwork for outside audits
complicate maintenance activities
create an avenue for dismissing craftsmen
4. Ultrasonic thickness readings at areas with surface temperatures above
______ are normally higher than actual thickness.
A.
B.
C.
D.
1000 F
2000 F
3000 F
2120 C
5. Flame detectors used to indicate a furnace or boiler fire may give erroneous
indications on control panels during:
A.
B.
C.
D.
Welding or related repairs on piping.
Piping alterations in the shop.
Ultrasonic inspection.
Radiographic inspection.
Page 2 - 16
6. Leaks in a threaded joint may be caused by:
A.
B.
C.
D.
Back-welding the fitting.
Lack of thread lubricant.
Under-pressuring the part.
Changing the direction of flow in the piping system.
7. A leaking threaded joint should not be tightened while the system is in
service under pressure because:
A.
B.
C.
D.
The craftsman should not be near the threaded connection.
Rust or corrosion might be holding the pressure.
The joint might be unscrewed.
A crack in a thread root might fail.
8. During a pressure test, care should be taken not to:
A.
B.
C.
D.
Allow any inert gas into the system.
Use water in the system.
Overpressure the system.
Underpressure the system.
9. Which of the following tests should not be used on cast iron piping:
A.
B.
C.
D.
Radiographic test
Leak test
Ultrasonic test
Hammer test
10. The details of inspection of in-service piping are provided in:
A. ASME IX
B. ASME B31.3
C. API 570
D. ASME B 16.5a
11. t = PD/2SE is the formula for:
A. Required Piping Thickness
B. Maximum Piping Thickness
C. Arbitrary Renewal Piping Thickness
D. Average Piping Thickness
12. API RP 574 is a:
A.
B.
C.
D.
Code
Standard
Specification
Recommended Practice
Page 2 - 17
13. During the manufacturing of tubing, the tubing may be welded, but is
generally:
A.
B.
C.
D.
Riveted.
Seamlessly drawn.
Wire drawn.
Forged.
14. A globe valve is commonly used to:
A. Prevent back flow.
B. Allow full flow.
C. Stop all flow.
D. Regulate fluid flow.
15. A check valve is commonly used to:
A. Prevent back flow.
B. Allow full flow.
C. Stop all flow.
D. Regulate fluid flow.
Page 2 - 18
API 574 Quiz
Answer Key
1. C
2. D
3. A
4. B
5. D
6. B
7. D
8. C
9. D
10. C
11. A
12. D
13. B
14. D
15. A
Paragraph 1.1
Paragraph 4.5.5
Paragraph 5.1
Paragraph 10.1.2.1
Paragraph 10.1.2.2
Paragraph 10.2.1.5.3
Paragraph 10.2.1.5.3
Paragraph 10.2.3
Paragraph 10.2.4
Paragraph 10.2.5
Paragraph 11.1
Foreword
Paragraph 4.2
Paragraph 4.3.3
Paragraph 4.3.8
Page 2 - 19
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Page 2 - 20
ASME B16.5
AN AMERICAN NATIONAL STANDARD
A
AS
SM
ME
E//A
AN
NS
SII B
B 1166..55aa--11999988
A
AD
DD
DEN
ND
DA
A
ttoo A
AS
SM
ME
E//A
AN
NS
SII B
B1166..55--11999966
Pipe Flanges and Flanged Fittings
NPS 1/2 Through NPS 24
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent API Committee interpretations.
The use of “Key Phrases” is intended as a study
guide only.
Page
P
age 3 - 1
(This page intentionally left blank)
Page 3 - 2
ASME/ANSI B 16.5a-1998
Addenda
to
ASME/ANSI B 16.5-1996
Pipe Flanges and Flanged Fittings
SECTION 1 - SCOPE
1.1. General
ASME/ANSI B 16.5 covers pressure-temperature ratings, materials,
dimensions, tolerances, marking, testing, and methods of designating
openings for pipe flanges and flanged fitting NPS 1/2 through NPS 24. Key
phrase "pipe flanges and fittings".
SECTION - 2 PRESSURE-TEMPERATURE RATINGS
This section is general information on flange temperature and pressure ratings
based on the type of flange, bolting and gasketing.
SECTION - 3 SIZE
3.1 Nominal Size
The size of flanges are covered by the nominal pipe size, NPS. Key phrase
"NPS".
Note: The new form for this designation is NPS 6, which was commonly 6”
pipe.
Page 3 - 3
SECTION 4 - MARKING
4.1 General
Flanges shall be marked as required in MSS SP-25. Key phrase “marked”.
The following shall be marked on the flange:
Manufacturer’s name or trademark
Material
cast - ASTM specification
plate - ASTM specification
Rating Class
Designation (B16 if conforms to this standard)
Temperature (none required)
Size
The letter R if Ring Joint Flange
Key phrase “marking”.
SECTION 5 - MATERIALS
5.1 General
The materials for flanges and flanged fittings have been grouped, see Tables 1
and 2. NOTE the groups are not numbered consecutively.
Key phrase “materials”.
5.3 Bolting
This section covers general bolting, (Table 1B) high strength bolting,
intermediate strength bolting, low strength bolting, bolting to gray cast iron
flanges and gaskets, Table 1B. Key phrase “bolting”.
SECTION 6 - DIMENSIONS
Dimensions for wall thickness, local areas, center-to-center and center-to-end flanges
and fittings. Faces and types, lapped joints, raised face, tongue and groove, ring
joint, blind flanges and flange facing finishes are generally discussed in this section.
Bolt holes, spot facing, welding end preparation reducing flanges, threads and
gaskets are also highlighted. Key phrase “dimensions”.
Page 3 - 4
SECTION 7 - TOLERANCES
Tolerances for center-to-center and center-to-end flanges and fittings. Faces and
types, lapped joints, raised face, tongue and groove, ring joint, hub dimensions and
bore of flanges are generally discussed in this section. Key phrase “tolerances”.
SECTION 8 - TEST
General test information about testing flanged fittings. Flanges are not required to
be hydrostatically tested. Key phrase “tests”.
The rest of this document is tables and diagrams used for reference and dimensions
of flanges and flanged fittings.
Page 3 - 5
(This page intentionally left blank)
Page 3 - 6
ASME B31.3
Process Piping
ASME Code For Pressure Piping
ASME B31.3 - 2002 Edition
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent interpretations. The use of “Key
Phrases” is intended as a study guide only.
Page 4 - 1
(This page intentionally left blank)
Page 4 - 2
Process Piping
ASME Code For Pressure Piping
ASME B31.3 - 2002 Edition
CHAPTER I
300 General Statements
This section covers general information about the B31.3 document, if this is
the first time the user has seen this document it is of general interest. Key
phrase “General information”.
300.1 Scope and Definitions
Rules for the Process Piping Code Section B31.3 have been developed
considering piping typically found in petroleum refineries; chemical,
pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and
related processing plants and terminals. Key phrase “Scope”.
300.1.1 Content and Coverage
Requirements for materials and components, design, fabrication, assembly,
erection, examination, inspection, and testing of pipe.
This code applies to piping for all fluids, including:
1. raw, intermediate, and finished chemicals;
2. petroleum products;
3. gas, steam, air, and water;
4. fluidized solids;
5. refrigerants; and
6. cryogenic fluids.
Key phrase “Code applications”.
300.2 Definitions
The student should read this section in great detail and become familiar with
the terms and definitions listed. For welding terms not shown in this section,
definitions in accordance with ANSI/AWS Standard A3.0 apply. Key phrase
“Definitions”.
Page 4 - 3
CHAPTER II
Design
(Included sections and excluded sections, see the API 570 Body of Knowledge.)
301.1 Qualifications of the Designer
The qualifications for the designer have now been added.
301.2 Design Pressure
The design pressure of each component in a piping system shall be not less
that the pressure at the most severe condition of coincident internal or
external pressure and temperature (minimum or maximum) expected during
service. Consideration must be given to pressure containment or relief in the
piping system. Key phrase “Design pressure”.
301.3 Design Temperature
The design temperature of each component in a piping system is the
temperature at which, under coincident pressure, the greatest thickness or
highest component rating is required. Fluid temperatures, ambient
temperatures, solar radiation, heating or cooling medium temperatures must
be considered. Key phrase “Design temperature”.
301.4 Ambient Effects
Ambient effects are in the form of cooling, fluid expansion atmospheric icing
all from atmospheric conditions. Key phrase “Ambient”.
301.5 Dynamic Effects
Impact, wind, earthquake, vibration and discharge reactions. Key phrase
“Dynamic”.
301.6 Weight Effects
Live loads and dead loads. Key phrase “Loads”.
301.7 Thermal Expansion and Contraction Effects
Loads due to restraints, temperature gradients, expansion characteristics,
movements of supports, and anchors, reduced ductility, cyclic, and air
condensation. Key phrase “Loads”.
302
Design Criteria
(This section has been excluded from the API 570 exam, except for Paragraph
302.3.4 and Table 302.3.4.)
302.3.4 Weld Joint Quality Factor, Ej. This paragraph applies only to the
longitudinal weld joint of piping. Girth welds are not addressed in this
section. Key phrase “Weld Quality Joint Factor”.
Page 4 - 4
Part 2 - Pressure Design of Piping Components
See table 326.1.
304.1 Straight Pipe
Required Thickness Eq. (2) :
tm = t + c
tm = minimum required thickness, including
mechanical, corrosion, and erosion allowances
t = pressure design thickness, as calculated
in accordance with para. 304.1.2 for internal pressure or as determined in
accordance with para 304.1.3 for external pressure
c = the sum of the mechanical allowances
(thread or groove depth) plus corrosion and erosion allowances. For
machined surfaces or grooves where the tolerance is not specified, tolerance
shall be assumed to be 0.5 mm (0.02 in.) in addition to the specified depth of
the cut.
Key phrase “Required Thickness”.
NOTE: The Barlow formula:
T = PD
2SE
has been removed from the 2000 addenda of B31.3, but is still listed in API
574.
304.1.3
Straight Pipe Under External Pressure
(This section has been excluded from the API 570 exam.)
Part 3 - Fluid Service Requirements For Piping Components
Material specifications for pipe and tube, API and ASTM. Key phrase
“Material specifications”.
Page 4 - 5
Part 4 - Fluid Service Requirements For Piping Joints
311
Welded Joints
Welded joints are allowed for any material which it is possible to qualify
welding procedures, welders, and welding operators, see Chapter V, B31.3.
Specific requirements for welds for Category D Fluid Service, Severe Cyclic
Conditions are mentioned in this section, refer to Table 341.4.2 and Table
341.4.3.
Buttwelds with backing rings, socket welds, fillet welds and seal welds may
be used, as well as open root welds. Key phrase “Welded joints”.
312
Flanged Joints
Note flange ratings and bolting torque. Key phrase “Flanged joints”.
313
Expanded Joints
Expanded joints may be used only under specific conditions. Key phrase
“Expansion joints”.
314
Threaded Joints
The rules for threaded joints are listed. Avoid crevice corrosion, severe
erosion, or cyclic loading conditions. Do not use thread sealing compounds
when threaded joints are to be seal welded. Give special consideration to
vibration and temperature cycling. Key phrase “Threaded joints”.
315
Tubing Joints
(This section has been excluded from the API 570 exam.)
Part 5 - Flexibility and Support
319
Piping Flexibility
Piping systems shall have sufficient flexibility to prevent thermal expansion
or contraction or movements of piping supports and terminals from causing
failure, leakage, and excessive thrusts or movements. Displacement strains
such as thermal displacement, restraint flexibility, externally imposed
displacements are defined in this section. Displacement stresses such as elastic
behavior, overstrained behavior must also be considered. Key phrase
“Flexibility”.
319.4 Flexibility Analysis
(This section has been excluded from the API 570 exam.)
Page 4 - 6
321
Piping Support
The design of support structures are based on acting loads, transmitted into
such supports and include weight effects, loads induced by service pressures
and temperatures, vibration, wind, earthquake, shock, and displacement
strain. Key phrase “Support”.
321.1.1 Objectives
The layout and design of piping and its supporting elements shall be
directed toward preventing the following:
1.
2.
3.
4.
5.
6.
7.
8.
9.
piping stresses;
leakage at joints;
excessive thrusts and moments on equipment;
excessive stresses in the supporting elements;
resonance with imposed or fluid-induced vibrations;
excessive interference with thermal expansion and contraction;
unintentional disengagement of piping from its supports;
excessive piping sag in piping requiring drainage slope;
excessive distortion or sag of piping subject to creep under
conditions of thermal cycling;
10. excessive heat flow, exposing supporting elements to
temperature extremes.
Support design is based on location, calculations and engineering
judgment. The details of pipe supports are outlined in the rest of this
section. Key phrase “Pipe supports”.
Part 6 – Systems
(This section has been excluded from the API 570 exam.)
Chapter III
Materials
323
General requirements
Chapter III states limitations and required qualifications for materials based
on their inherent properties. Key phrase “Materials”.
Page 4 - 7
323.1 Materials and Specifications
Materials must conform to listed specifications. Unlisted materials may
be used provided they conform to a published specification and meet
the requirements of this code. Note materials of unknown
specification shall not be used for pressure containing piping
components. Reclaimed materials may be used, providing they are
properly identified. Most materials have upper and lower
temperature limits, see Table 323.2.2. Key phrase “Material
specifications”.
323.3 Impact Test Methods and Acceptance Criteria
Of special interest is the impact testing methods and acceptance
criteria. The procedure and test specimen requirements are listed, see
Figure 323.2.2A Minimum Temperatures Without Impact Testing for
Carbon Steel Materials and Table 323.3.1 Impact Testing Requirements
for Metals. Test temperatures for all Charpy impact tests shall be
observed, see paragraph. 323.4 a or b. Acceptance criteria is shown in
Table 323.5 The requirements for lateral expansion, weld impact test
and other related tests are listed in this section. Key phrase “Impact
test”.
Chapter IV
Standards for Piping Components
This section gives the dimensions and ratings of piping components. Key
phrase “Dimensions and ratings”.
Chapter V
Fabrication, Assembly, And Erection
328.1 Welding Responsibility
Each employer is responsible for the welding done by the personnel of
his organization and shall conduct the tests required to qualify welding
procedures, and to qualify and as necessary requalify welders and
welding operators. Key phrase “Responsibility”.
328.2 Welding Qualifications
Welders and welding operators must be qualified to ASME Section IX,
except as modified by B31.3. The general details are listed in this
section. Special attention should be given to sub-paragraph f, this
paragraph allows Table A - 1 when matching P-Numbers and SNumbers. Key phrase “Welding qualifications”.
Page 4 - 8
328.2.2 Procedure Qualification by Others
Each employer is responsible for qualifying any welding
procedure that personnel of the organization will use. Subject
to the specific approval of the Inspector. The Inspector shall be
satisfied that:
1. the proposed WPS has been prepared, qualified, and
executed by a responsible, organization with expertise in the
field of welding; and
2. the employer has not made any change in the welding
procedure.
Key phrase “Procedure qualification by others”.
328.2.3 Performance Qualification by Others
To avoid duplication of effort, an employer may accept a
performance qualification made for another employer,
provided the Inspector specifically approves. Acceptance is
limited to qualification on piping using the same procedure
wherein the essential variables are within the limits in Section
IX. Key phrase “Performance qualification by others”.
328.2.4 Qualification Records
The employer shall maintain a self-certified record, available to
the Inspector of procedures and welders employed. Key phrase
“Qualification records”.
328.3.1 Welding Materials
Filler metal shall conform to Section IX. Others may be used
with the owner’s approval if a procedure qualification test is
first successfully made. Key phrase “Filler metals”.
328.4 Preparation for Welding
Internal and external surfaces to be cut or welded shall be clean and
free from paint, oil, rust, scale and other material that can be
detrimental to the weld. End preparation is acceptable only if the
surface is reasonably smooth and true, and slag is removed. Groove
weld details are found in 328.4.2. Alignment shall be aligned within the
dimensional limits in the WPS and the engineering design. Key phrase
“Weld prep.”.
Page 4 - 9
328.5 Welding Requirements
•
•
•
•
•
Welds shall be made in accordance with a qualified procedure and
by qualified welders or welding operators.
Each welder shall be assigned an identification symbol. The welds
shall be marked or appropriate records shall be filed.
Tack welds shall be made with filler metal equivalent to that used in
the root pass. Tack welds shall be made by a qualified welder.
Tack welds shall be fused with the root pass, cracked tacks shall be
removed, bridge tacks shall be removed.
Peening is prohibited on the root pass and final pass of a weld.
No welding shall be done if there is impingement on the weld area
of rain, snow, sleet, or excessive wind, or if the weld area is frosted
or wet.
Details of fillet and socket welds, seal welds, welded branch connection
welds are given in this section. Key phrase “Weld requirements”.
328.6 Weld Repair
A weld defect to be repaired shall be removed to sound metal. Repair
welds shall be made using a qualified welding procedure. Key phrase
“Weld repair”.
330
Preheating
Preheating is used to minimize the detrimental effects of high temperature
and severe thermal gradients inherent in welding. Minimum recommended
preheat temperatures are given in Table 330.1.1. If the ambient temperature
is below freezing, the recommendations in Table 330.1.1 become
requirements. The preheat zone shall extend at least 1 inch beyond each edge
of the weld. Key phrase “Preheating”.
331
Heat Treatment
Heat treatment is used to avert or relieve the detrimental effects of high
temperature and severe temperature gradients inherent in welding, and to
relieve residual stresses created by bending and forming. General heat
treatment requirements include Table 331.1.1 (thickness and material
grouping ranges) and must be specified in the WPS. The rest of this section
deals with the specific requirements for heat treatment. Key phrase “Heat
treatment”.
Page 4 - 10
Chapter VI
Inspection, Examination, and Testing
340
Inspection - General
The term “Inspector” refers to the owner’s Inspector or the Inspector’s
delegates. It is the owner’s responsibility, through the owner’s Inspector, to
verify that all required examinations and testing have been completed and to
inspect the piping to the extent necessary to be satisfied that it conforms to all
applicable examination requirements of the Code and the engineering design.
The Inspector shall have access to any place where work concerned with the
piping installation is being performed. The Inspector shall be designated by
the owner and shall be the owner, an employee of the owner, an employee
of an engineering or scientific organization, or of a recognized insurance or
inspection company acting as the owner’s agent. The Inspector shall have not
less than 10 years experience in the design, fabrication, or inspection of
industrial pressure piping. Key phrase “Inspector”.
341
Examination
Examination applies to quality control functions performed by the
manufacturer. Inspection does not relieve the manufacturer of the
responsibility for:
• providing materials, components, and workmanship
• performing all required examinations; and
• preparing suitable records of examinations and tests for the Inspector’s
use.
The examiner shall be assured, by examination of certifications, records, and
other evidence, that the materials and components are of the specified grades
and that they have received required heat treatment, examination, and
testing. The examiner shall provide the Inspector with a certification that all
the quality control requirements of the code and the engineering design have
been carried out. Key phrase “Examination”.
342
Examination Personnel
Examiners shall have training and experience commensurate with the needs
of the specified examinations (ASNT SNT-TC-1A). Certifications by
employers are recognized. Note, for in-process examination, the
examinations shall be performed by personnel other than those performing
the production work. Key phrase “Examiners”.
343
Examination Procedures
Any examination shall be performed in accordance with a written procedure
that conforms to ASME Section V. Key phrase “Examination procedures”.
Page 4 - 11
344
Types of Examination
• 100% - complete examination
• random - complete examination of a percentage
• spot - partial examination
• random spot - a specified partial examination of a percentage
Key phrase “Examination”.
344.2 Visual Examination
Visual examination (VT) is observation of the portion of components,
joints, and other piping elements that are or can be exposed to view
before, during, or after manufacture, fabrication, assembly, erection,
examination, or testing. Visual examination shall be performed in
accordance with ASME Section V, Article 9. Key phrase “VT”.
344.3 Magnetic Particle Examination
Magnetic Particle (MT) examination shall be performed in accordance
with Section V, Article 7. Key phrase “MT”.
344.4 Liquid Penetrant Examination
Liquid Penetrant (PT) examination shall be performed in accordance
with Section V, Article 6. Key phrase “PT”.
344.5 Radiographic Examination
Radiographic (RT) examination shall be performed in accordance with
Section V, Article 2.
• 100% - applies only to girth and miter groove welds and to
fabricated branch connection welds.
• Random Radiography - Applies only to girth and miter groove
welds.
• Spot Radiography - A single exposure radiograph.
Key phrase “RT”.
344.6 Ultrasonic Examination
Ultrasonic (UT) examination shall be performed in accordance with
Section V, Article 5. Note: acceptance criteria is listed in paragraph
344.6.2. Key phrase “UT”.
344.7 In-Process Examination
In-process examination includes joint preparation and cleanliness;
preheating; preheating; fit-up, joint clearance, and internal alignment;
variables specified by the procedure, including filler metal and
position; condition of the root pass, slag removal and weld condition
between passes; and appearance of the finished joint. The examination
is visual. Key phrase “In-process examination”.
Page 4 - 12
345
Testing
Leak test, including hydrostatic, pneumatic or a combined hydrostaticpneumatic test. Details of testing are listed in this section. Key phrase “Leak
testing”.
346
Records
It is the responsibility of the piping designer, the manufacturer, the fabricator,
and the erector, as applicable, to prepare the records required by B 31.3.
Examination procedures and examination personnel qualifications records
shall be retained for at least 5 years after the record is generated. Key phrase
“Records”.
Chapter VII
Nonmetallic Piping and Piping Lined With Nonmetals
(This section has been excluded from the API 570 exam.)
Chapter VIII
Piping for Category M Fluid Service
(This section has been excluded from the API 570 exam.)
Chapter IX
High Pressure Piping
(This section has been excluded from the API 570 exam.)
Appendix A
Allowable Stresses And Quality Factors For Metallic Piping
And Bolting Materials
Table A1 - Table A2 (Note with the introduction of Addenda 96 and 97, many
of the stress values have changed.)
Page 4 - 13
Appendix B
Stress Tables and Allowable Pressure Tables for Nonmetals
(This section has been excluded from the API 570 exam.)
Appendix C
Physical Properties of Piping Materials
Table C1 - C8
Appendix D
Flexibility and Stress Intensification Factors
(This section has been excluded from the API 570 exam.)
Appendix E
Reference Standards
(This section has been excluded from the API 570 exam.)
Appendix F
Precautionary Considerations
Appendix G
Safeguarding
(This section has been excluded from the API 570 exam.)
Appendix H
Sample Calculations for Branch Reinforcement
(This section has been excluded from the API 570 exam.)
Page 4 - 14
Appendix J
Nomenclature
(This section has been excluded from the API 570 exam.)
Appendix K
Allowable stresses for High Pressure Piping
(This section has been excluded from the API 570 exam.)
Appendix L
Aluminum Alloy Pipe Flanges
Appendix M
Guide To Classifying Fluid Services
Appendix Q
Quality System Program
Appendix V
Allowable Variations In Elevated
Temperature Service
Appendix X
Metallic Bellows Expansion Joints
(This section has been excluded from the API 570 exam.)
Appendix Z
Preparation of Technical Inquiries
(This section has been excluded from the API 570 exam.)
Index
This can be an extremely useful tool in looking for items in B 31.3. General
notes follow the index.
Page 4 - 15
ASME B31.3
Quiz
1.
All welding terms found in ASME B31.3 are found in the Code and:
A.
B.
C.
D.
2.
A fluid service in which the potential for personnel exposure is judged to be
significant:
A.
B.
C.
D.
3.
Category M Fluid Service
High Pressure Fluid Service
Normal Fluid Service
Category B Fluid Service
Snow and ice loads due to both environmental and operating conditions are
considered:
A.
B.
C.
D.
4.
ASME Section IX
ASME Section V
AWS A2.4
AWS A3.0
Dead Loads
Live Loads
Environmental Loads
Structural Loads
The required thickness of straight sections shall be determined in accordance
with Eq. 2,
A.
B.
C.
D.
tm = t + d
tm = d - t
tm = t + c
tm = c - t
Page 4 - 16
5.
Socket welds should:
A. be avoided in the piping system
B. be used in all welded piping
C. be welded using SAW only
D. be avoided where crevice corrosion may occur.
6. A Charpy V-notch specimen for impact testing shall be made using a
A.
B.
C.
D.
7.
E7018
E7016
E6024
E6010
A welder may pass a performance qualification test for Company A, quit the
job, then be hired by Company B, to perform similar work, and not have
to retest.
A.
B.
C.
D.
11.
by others may be used
by the employer only may be used
by the use of AWS prequalified, D1.1 type procedures, may be used
by the use of API 1104 qualified procedures may be used
A cellulose DCEP Electrode in the AWS A5.1 is:
A.
B.
C.
D.
10.
ASME B 31.3
BPV Code, Section IX
API 570
Both A and B
Subject to the specific approval of the Inspector, welding procedures
qualified:
A.
B.
C.
D.
9.
1/2” square cross section
10 M square cross section
10 mm square cross section
.505 “ square cross section
Qualification of welding procedures to be used in compliance with
ASME B 31.3 shall conform to the requirements of:
A.
B.
C.
D.
8.
standard:
True
False
True only in certain states
False, in compliance with ASME B 31.3
Filler metal shall conform to the requirements of:
A.
B.
C.
D.
AWS A5.1
Section IX
Section V
API 570
Page 4 - 17
12.
Circumferencial welds inside surfaces of groove welds shall be aligned:
A.
B.
C.
D.
13.
The root pass and final pass of a weld may not be:
A.
B.
C.
D.
14.
peened
cleaned
stress relieved
painted
A threaded joint may be seal welded by a qualified welder if:
A.
B.
C.
D.
15.
+ or - 1/16”
+ or - 1/32”
within the dimensional limits in the WPS
the fabricator’s discretion
the joint is leaking
the joint has straight threads only
the joint has tapered threads only
all exposed threads are covered
The preheat zone shall extend at least ____ beyond the edge of the weld.
A. 10 mm
B. 1 inch
C. 50 mm
D. 3 inches
16.
The owner’s Inspector shall have:
A.
B.
C.
D.
17.
an API 570 Certification
an AWS CWI Certification
an API 510 Certification
not less than 10 years experience dealing with piping
In reviewing radiography of a Normal Fluid Service piping weld a crack was
noticed. If the pipe wall was .375, what length crack is acceptable?
A. none
B. T/3
C. 3/16”
D. cracks will not show on radiographs
18.
An examiner performing a PT test of a completed weld on the outside of a
Category D Fluid Service piping system noted a transverse crack in the
root pass:
A.
B.
C.
D.
The weld is acceptable
The PT test should be repeated
The welder should be requalified
The PT test will not show this type of discontinuity from the outside.
Page 4 - 18
19.
Individual slag trapped in a weld in Severe Cyclic Conditions piping system,
maximum length may be:
A. >TwX3
B. Tw/3
C. 12 T
D. 3/23 “
20.
Examiners may be qualified in compliance with:
A.
B.
C.
D.
ASME Section IX
ASME Section V
ASNT SNT-TC-1A
API 570
Page 4 - 19
API ASME B31.3 Quiz
Answer Key
1. D
2. A
3. B
4. C
5. D
6. C
7. D
8. A
9. D
10. A
11. B
12. C
13. A
14. D
15. B
16. D
17. A
18. D
19. B
20. C
(Paragraph 300.2 Page 2)
(Para. 300.2 b page 5)
(Para. 301.6.1 page 13)
(Para. 304.1.1 a Page 19)
(Para. 311.2.4 Page 35)
(Para. 323.3.3 Page 53)
(Para. 328.2.1a Page 60)
(Para. 328.2.2 Page 60)
(Para. 328.2.2g Page 61)
(Para. 328.2.3 Page 61)
(Para. 328.3 Page 61)
(Para. 328.4.3 Page 62)
(Para. 328.5.1d Page 63)
(Para. 328.5.3 Page 65)
(Para. 330.1.4 Page 67)
(Para. 340.4 Page 75)
(Table 341.3.2 Page 77)
(Table 341.3.2 Page 77)
(Table 341.3.2 Page 77)
(Para. 342.1 Page 82)
Page 4 - 20
ASME Section V
Nondestructive Examination
API 570 - 1998 Edition, including 2000 and 2001
Addenda
ASME B31.3 - 2002 Edition
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent interpretations
Page 5 - 1
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Page 5 - 2
API 570
Nondestructive Examination
API 570 Paragraph 8.2.5
Acceptance of a welded repair or alteration shall include NDE in accordance
with the applicable code and the owner-user’s specification, unless otherwise
specified in API 570. Note, the applicable code is usually ASME B31.3.
ASME B 31.3, Paragraph 342 Examination Personnel
Examiners shall have training and experience commensurate with the needs
of the specified examinations. (Footnote 1, For this purpose, SNT-TC-1A,
Recommended Practice for Nondestructive Testing Personnel Qualification
and Certification, may be used as a guide.) The employer shall certify records
of the examiners employed, showing dates and results of personnel
qualifications, and shall maintain them and make them available to the
Inspector.
ASME B 31.3 Requirements for Nondestructive Testing Procedures and Personnel
Certification.
The American Society for Nondestructive Testing, Inc. Recommended Practice SNTTC-1A is recognized for technician qualifications (Examiners) in some NDE
techniques.
SNT-TC-1A is a document that outlines requirements for Personnel Qualification
and Certification in Nondestructive Testing, the main items listed are:
Work Experience
Training
Education
Testing
In order to qualify as an ASNT Level II, Radiographers must have:
12 Months Job Experience
79 Hours Formal Training
High School Graduation
Level II Exam, General, Specific and Practical
In order to qualify as an ASNT Level II, Ultrasonic Technicians must have:
12 Months Job Experience
80 Hours Formal Training
High School Graduation
Level II Exam, General, Specific and Practical
Page 5 - 3
ASME B31.3, Paragraph 343 Examination Procedures
Any examination shall be performed in accordance with a written procedure
that conforms to one of the methods specified in paragraph 344, including
special methods. Procedures shall be written as required in ASME Section V,
Article 1, paragraph T-150.
ASME B31.3, Paragraph 344 Types of Examination
ASME B 31.3, Paragraph 344.1.3 Definitions
•
•
•
•
100% - complete examination
random - complete examination of a percentage
spot - partial examination
random spot - a specified partial examination of a percentage
ASME B 31.3, Paragraph 344.2 Visual Examination
Visual examination (VT) is observation of the portion of components, joints,
and other piping elements that are or can be exposed to view before, during,
or after manufacture, fabrication, assembly, erection, examination, or testing.
Visual examination shall be performed in accordance with ASME Section V,
Article 9.
ASME B 31.3, Paragraph 344.3 Magnetic Particle Examination
Magnetic Particle (MT) examination shall be performed in accordance with Section
V, Article 7.
ASME B 31.3 Magnetic Particle Method
Page 5 - 4
MT Principles of Operation
Basically, an object or localized area is magnetized through the use of AC or
DC current. Once the area is magnetized lines of flux are formed. See
previous page. Dry iron powder, or iron powder held in suspension is added
to the surface of the test piece. Any interruption in the lines of flux will create
an indication which can be evaluated. The process may be used on any
material that is ferromagnetic. This method of NDE can be used in visible
light or with special powders, under black light. Surface discontinues are the
most commonly detected indications using this process.
This process will detect:
Surface and slightly subsurface defects only!
Magnetic Particle Method
Study Notes
Read ASME Section V, Article 7
Study Notes:
Page Number:
Standard/Code
Calibration requirements
_______________
___________
Yoke weight requirements,
both AC and DC
_______________
___________
General MT procedure
requirements
_______________
___________
Know where to find:
Page 5 - 5
ASME B 31.3, Paragraph 344.4 Liquid Penetrant Examination
Liquid Penetrant (PT) examination shall be performed in accordance with
Section V, Article 6.
Liquid Penetrant Method
PT Principles of Operation
Penetrant testing is a family of testing that can be divided into two major groups,
visible light and fluorescent or “Black Light” detectable groups. The basic steps of
the operation can be seen above. Step 1: the test piece must be cleaned. Step two:
the penetrant is applied, a dwell time or soaking time waited. Step three: the excess
penetrant is removed. Step four:, the developer applied. Step five: the part is
inspected, any indication is evaluated. Step six: the part is post cleaned.
This inspection technique relies on the penetrant being pulled into all surface
irregularities by capillary action. When the developer is applied, the penetrant is
blotted back to the surface making the irregularities visible. The irregularities are
then evaluated into three groups, false indications, commonly called handling
marks, non-relevant indications and defects. The defects are evaluated to a given
standard for acceptance.
This process will detect:
Surface defects only!
Page 5 - 6
Liquid Penetrant Method
Study Notes
Read ASME Section V, Article 6
Study Notes:
Page Number:
Standard/Code
Test temperatures
_______________
___________
Surface temperatures
_______________
___________
General PT procedure
requirements
_______________
___________
Know where to find:
Page 5 - 7
ASME B 31.3, Paragraph 344.5 Radiographic Examination
Radiographic (RT) examination shall be performed in accordance with Section
V, Article 2.
• 100% - applies only to girth and miter groove welds and to fabricated
branch connection welds.
• Random Radiography - Applies only to girth and miter groove welds.
• Spot Radiography - A single exposure radiograph.
This process will detect:
Surface and subsurface defects!
Radiographic Examination
IQI
Shim
17
Weld
1
1 ASTM B
2
RT Principles of Operation
Radiography is a nondestructive test method based on the principle of preferential
radiation transmission. Areas of reduced thickness or lower density transmit more,
and therefore absorb less, radiation. The radiation which passes through a test
object forms a shadow image on a film. X-rays are man-made.
Subsurface discontinuities which are readily detected by this method are voids,
metallic and nonmetallic inclusions, and favorably aligned incomplete fusion and
cracks.
Page 5 - 8
Radiographic Examination Study Notes
Read ASME Section V, Article 2
Study Notes:
Page Number:
Standard/Code
Backscatter acceptability
_______________
___________
Geometric Unsharpness
_______________
___________
IQI information
_______________
___________
Density
_______________
___________
Location Markers
_______________
___________
General RT procedure
requirements
_______________
___________
Know where to find:
Page 5 - 9
ASME B 31.3, Paragraph 344.6 Ultrasonic Examination
Ultrasonic (UT) examination shall be performed in accordance with Section V,
Article 5. Note acceptance criteria is listed in paragraph 344.6.2.
Ultrasonic Method
UT Principles of Operation
Ultrasonic testing utilizes high frequency sound waves, well above the range of
human hearing, to measure geometric and physical properties in materials.
Ultrasonic testing will best detect those more critical planar discontinuities such as
cracking and incomplete fusion. UT is most sensitive to discontinuities which lie
perpendicular to the sound beam. Because various beam angles can be achieved
with transducers and Plexiglas wedges the process can detect laminations,
incomplete fusion and cracks that are oriented such that detection with radiographic
testing would not be possible. The process has deep penetration ability and can be
very accurate. This test method is generally limited to the inspection of butt welds
in materials that are thicker than 1/4 inch.
This process will detect:
Surface and subsurface defects,
will detect some defects not readily
detectable by radiography!
Page 5 - 10
Ultrasonic Testing Study Notes
Read ASME Section V, Article 5
Study Notes:
Page Number:
Standard/Code
Acceptance criteria
_______________
___________
Linear-type discontinuity
_______________
___________
Calibration blocks
_______________
___________
General UT procedure
requirements
_______________
___________
Know where to find:
Page 5 - 11
ASME B 31.3, Paragraph 345.8 - Sensitive Leak Test
The test (leak test) shall be in accordance with the gas and bubble test method
specified in PBV Code, Section V, Article 10, or by another method demonstrated to
have equal sensitivity.
ASME Section V, Article 10 - Leak Testing
This article gives the general procedure for the performance of leak testing.
Study Notes:
Page Number:
Standard/Code
Procedure Requirements
_______________
___________
Calibration Requirements
_______________
___________
Report
_______________
___________
Know where to find:
Data
Page 5 - 12
Nondestructive Examination
Quiz
1.
_______________ tests leave the test object unchanged and ready to be
placed in service, if acceptable.
a.
b.
c.
d.
e.
2.
_______ inspection is considered to be the primary nondestructive test
method.
a.
b.
c.
d.
e.
3.
Penetrant
Ultrasonic
Magnetic particle
Visual
none of the above
Visual inspection must be performed _________________.
a.
b.
c.
d.
e.
4.
Destructive
Nondestructive
Bend
all of the above
none of the above
before welding
during welding
after welding
all of the above
none of the above
_________ tests reveals surface discontinuities by the bleedout of a
penetrating medium against a contrasting background.
a.
b.
c.
d.
e.
Penetrant
Ultrasonic
Magnetic particle
Visual
none of the above
Page 5 - 13
5.
The visible dye used in PT produces a vivid _____ indication against a
white background.
a.
b.
c.
d.
e.
6.
The fluorescent dye used in PT produces a ______ fluorescent indication
against a light background when observed under an ultraviolet light.
a.
b.
c.
d.
e.
7.
surface indications
cracks
overlap
all of the above
none of the above
The ________ method is used to discover surface or slightly subsurface
discontinuities in ferromagnetic materials.
a.
b.
c.
d.
e.
9.
greenish
red
neutral
all of the above
none of the above
PT will not detect ________.
a.
b.
c.
d.
e.
8.
greenish
red
neutral
all of the above
none of the above
penetrant
ultrasonic
magnetic particle
visual
none of the above
When the magnetic field is oriented along the axis of the part, it is referred
to as ________ magnetism.
a.
b.
c.
d.
e.
circular
diagonal
longitudinal
all of the above
none of the above
Page 5 - 14
10.
When the magnetic field tends to surround the part perpendicular to its
longitudinal axis, it is referred to as ________ magnetism.
a.
b.
c.
d.
e.
11.
circular
diagonal
longitudinal
all of the above
none of the above
A ________ field results when the "yoke" method is used, as shown in
figure 11.
a.
b.
c.
d.
e.
circular
diagonal
longitudinal
all of the above
none of the above
Figure 11
12.
A ________ field results when the "prod" technique is used, as shown in
figure 12.
a.
b.
c.
d.
e.
circular
diagonal
longitudinal
all of the above
none of the above
Figure 12
13.
The major limitation of magnetic particle testing is that it will work only
on ________ material.
a.
b.
c.
d.
14.
any stainless
any copper
any lead
any ferromagnetic
_______ is a nondestructive test method based on the principle of
preferential radiation transmission.
a.
b.
c.
d.
e.
Penetrant
Ultrasonic
Magnetic particle
Visual
none of the above
Page 5 - 15
15.
The disadvantages of radiographic testing are _________________.
a.
b.
c.
d.
e.
16.
________ is a nondestructive inspection method which uses high
frequency sound waves to measure geometric and physical properties in
materials.
a.
b.
c.
d.
e.
17.
radiation exposure
extensive safety training
the process may not detect laminations
all of the above
none of the above
Penetrant
Ultrasonic
Magnetic particle
Visual
none of the above
A major limitation of ultrasonic testing is that it requires a ________
because interpretation can be difficult.
a.
b.
c.
d.
complex reference guide
complex standard test block
extensive calibration tests
skilled operator
Page 5 - 16
Nondestructive Examination
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
b
d
d
a
b
a
e
c
c
a
c
a
d
e
d
b
d
Page 5 - 17
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Page 5 - 18
Welding Processes
WELDING AND CUTTING PROCESSES
Introduction
Since the welding inspector is primarily concerned with welding, knowledge of the
various joining and cutting processes can be very helpful. While it is not mandatory
that the inspector be a qualified welder, any hands-on welding experience is a
benefit. In fact, many welding inspectors are selected for that position after working
as a welder for some time. History has shown that former welders often make
good inspectors.
There are certain aspects of the various joining and cutting processes which the
successful welding inspector must understand in order to perform the job most
effectively. First, the inspector should realize the important advantages and
limitations of each process. The individual should also be aware of those
discontinuities which may result when a particular process is utilized. Many
discontinuities occur regardless of the process used; however, there are others
which can occur due to the misapplication of a particular process. These will be
discussed for each method and referred to as possible problems.
The welding inspector should also have some knowledge of the equipment
requirements for each process, because often discontinuities occur which are the
result of equipment deficiencies. The inspector should be somewhat familiar with
the various machine controls and what effect their adjustment will have on the
resulting weld quality.
When the welding inspector has some understanding of these process
fundamentals, they are better prepared to perform visual welding inspection. This
knowledge will aid in the discovery of problems when they occur rather than later
when the cost of correction is greater. The inspector who is capable of spotting
problems in-process will be a definite asset to both production and quality control.
Another benefit of having experience with these methods is that the production
welders will have greater respect for the inspector and the inspector’s decisions.
Also, a welder is more likely to bring some problem to the inspector's attention if it
is known that the inspector understands the practical aspects of the process. So,
having this knowledge will help the inspector get better cooperation from the
welders and others involved with the fabrication operation.
The processes presented here can be divided into two basic groups: welding and
cutting. Welding describes a method for joining metals while cutting results in the
removal or separation of material. As each of the joining and cutting processes are
discussed, there will be an attempt to describe their important features, including:
Page 6 - 1
process advantages, process limitations, equipment requirements, electrodes/filler
metals, techniques, applications, and possible process problems.
There are numerous joining and cutting processes available for use in the fabrication
of metal products. This fact is supported by the American Welding Society's "Master
Chart of Welding and Allied Processes." This chart separates the joining and cutting
methods into various categories, namely: Welding Processes and Allied Processes.
The Welding Processes are further divided into seven groups: Arc Welding, SolidState Welding, Resistance Welding, Oxyfuel Gas Welding, Soldering, Brazing, and
Other Welding. The Allied Processes include: Thermal Spraying, Adhesive Bonding,
and Thermal Cutting (Oxygen, Arc and Other Cutting).
With so many different processes available, it would be difficult to describe each one
within the scope of this course. The following processes will be described:
Welding Processes
• Shielded Metal Arc Welding
• Gas Metal Arc Welding
• Flux Cored Arc Welding
• Gas Tungsten Arc Welding
• Submerged Arc Welding
• Plasma Arc Welding
• Oxyacetylene Welding
Cutting Processes
• Oxyfuel Cutting
• Air Carbon Arc Cutting
• Plasma Arc Cutting
• Mechanical Cutting
Page 6 - 2
Welding Processes
Before exploring the various welding processes, it is appropriate to define what is
meant by the term "welding." According to AWS, a weld is: "a localized coalescence
[joining together] of metals or nonmetals produced either by heating the materials
to the welding temperature, with or without the application of pressure, or by the
application of pressure alone and with or without the use of filler metal." Therefore,
welding refers to the operations used to accomplish this joining. This section will
present important features of some of the more common welding processes, all of
which employ the use of heat without pressure.
As each of these welding processes are presented, it is important to note that they all
have certain features in common. That is, there are certain elements which must be
provided by the welding process in order for it to be capable of producing
satisfactory welds. These features include: some source of energy to provide
heating, some means of shielding the molten metal from the atmosphere, and a
filler metal (optional with some processes and joint configurations). The processes
differ from one another because they provide these same features in various ways.
So, as each process is introduced, be aware of how it satisfies these requirements.
Shielded Metal Arc Welding (SMAW)
The first process to be presented is shielded metal arc welding (SMAW). Even
though this is the correct name for the process, it is more referred to as "stick
welding." This process operates by heating the metal with an electric arc between a
covered metal electrode and the metals to be joined. The arc is created between the
electrode and the workpiece due to the flow of electricity. This arc provides heat, or
energy, to melt the base metal, filler metal and electrode coating. As the welding arc
progresses to the right, it leaves behind solidified weld metal covered by a layer of
solidified flux, or slag. This slag tends to float to the outside of the metal since it
solidifies after the molten metal has solidified so there is less likelihood that it will be
trapped inside the weld zone resulting in a slag inclusion.
Another feature is the presence of shielding gas which is produced when the
electrode coating is heated and decomposed. These gases assist the flux in the
shielding of the molten metal in the arc region.
The primary element of the shielded metal arc welding process is the electrode itself.
It is made up of a solid metal core wire covered with a layer of granular flux held in
place by some type of bonding agent. All carbon and low alloy steel electrodes
utilize essentially the same type of steel core wire---a low carbon, rimmed steel.
Any alloying is provided from the coating, since it is more economical to achieve
alloying in this way.
Page 6 - 3
The electrode coating is the feature which classifies the various types of electrodes.
It actually serves five separate functions:
1.
SHIELDING: decomposes to form gaseous shield for molten
metal
2.
DEOXIDIZATION: fluxing action removes oxygen and other
atmospheric gases
3.
ALLOYING: provides additional alloying elements for weld
deposit
4.
IONIZING: improves electrical characteristics to increase arc
stability
5.
INSULATING: solidified slag provides insulating blanket to
slow down weld metal cooling rate. (minor effect)
Since the electrode is such an important feature of the shielded metal arc welding
process, it is necessary to understand how the various types are classified and
identified. American Welding Society Specifications A5.1 and A5.5 describe the
requirements for carbon and low alloy steel electrodes, respectively. They describe
the various classifications and characteristics of these electrodes. The American
Welding Society has also developed a system for the identification of shielded metal
arc welding electrodes.
The identification consists of an "E", which stands for electrode, followed by four or
five digits. The first two or three numbers refer to the minimum tensile strength of
the deposited weld metal. These numbers state the tensile strength in thousands of
pounds per square inch. For example, "70" means that the tensile strength of the
deposited weld metal is at least 70,000 psi.
The next number refers to the positions in which the electrode can be used. A "2"
means that the molten metal is so fluid that the electrode can only be used in the flat
or horizontal fillet positions. A "1" tells us that the electrode is suitable for use in any
position.
The last number describes the usability of the electrode which is determined by the
composition of the coating present on the electrode. This coating will determine its
operating characteristics and recommended electrical current---AC (alternating
current), DCEP (direct current-electrode positive) or DCEN (direct current-electrode
negative).
It is important to note that those electrodes ending in "5," "6" or "8" are classified as
low hydrogen types. To maintain this low moisture content, they must be stored in
their original factory-sealed container or an acceptable storage oven. This oven
should be heated electrically and have temperature control capability in the range of
o
150o to 350 F. Since this device will assist in the maintenance of a low moisture
content (less than 0.2%) it must be suitably vented. Any low hydrogen electrodes
which are not to be used immediately should be placed into the holding oven as
soon as their air-tight container is opened.
Page 6 - 4
1
However, it is important to note that electrodes other than those mentioned above
may be harmed if placed in the oven. Some electrode types are designed to have a
certain moisture level. If this moisture is eliminated, the operating characteristics of
the electrode will deteriorate significantly.
Those SMAW electrodes used for joining low-alloy steels may also have an alphanumeric suffix which is added to the standard designation after a hyphen.
Suffix to Electrode Designation Major Alloy Element(s)
A1 0.5% Molybdenum
B1 0.5% Molybdenum-0.5% Chromium
B2 0.5% Molybdenum-1.25% Chromium
B3 1.0% Molybdenum-2.25% Chromium
B4 0.5% Molybdenum-2.0% Chromium
C1 2.5% Nickel
C2 3.5% Nickel
C3 1.0% Nickel
D1 0.3% Molybdenum-1.5% Manganese
D2 0.3% Molybdenum-1.75% Manganese
G* 0.2% Molybdenum; 0.3% Chromium;
0.5% Nickel; 1.0% Manganese;
0.1% Vanadium
* Need have minimum content of one element only.
The equipment for shielded metal arc welding is relatively simple. One lead from
the welding power source is connected to the piece to be welded and the opposite
lead goes to the electrode holder into which the welder places the welding electrode
to be consumed. The electrode and base metal are melted by the heat produced
from the welding arc created between the end of the electrode and the workpiece
when they are brought close together.
The power source for shielded metal arc welding is referred to as a constant current
power supply, having a "drooping" characteristic. This terminology can be more
easily understood by looking at the characteristic volt-ampere (V-A) curve for this
type of power supply.
As can be seen in the typical volt-ampere curves, a decrease in arc voltage will result
in a corresponding increase in arc current. This is significant from a process- control
standpoint because the arc voltage is directly related to the arc length (distance from
electrode to workpiece). That is, as the welder moves the electrode toward or away
from the workpiece, the arc voltage is actually being decreased or increased.
These voltage changes correspond with changes in the arc current, or the amount of
heat created by the welding arc. So as the welder draws the electrode away from
the workpiece, the arc length increases which reduces the current, and consequently,
the heat to the weld. A shorter arc length results in a higher arc current, and
therefore increased heating. So, even though there is a control on the welding
Page 6 - 5
machine for current, the welder has some capability to instantaneously alter the
current at the arc by manipulating the electrode to provide longer or shorter arc
lengths.
Because the lower curve has less slope than the upper curve, a greater change in arc
current is obtained from a given change in arc length (voltage). Modern power
supplies utilize controls which vary the open circuit voltage (OCV) and slope to
produce a welding current having good operator control and the proper magnitude.
Shielded metal arc welding is utilized in most industries for numerous applications.
It is used for most materials except for some of the more exotic alloys. Even though
it is a relatively old method and newer processes have replaced it in some
applications, shielded metal arc welding remains as a popular process which will
continue to be greatly utilized by the welding industry.
There are several reasons why the process continues to be popular. The equipment
is relatively simple and inexpensive. This helps to make the process quite portable.
In fact, there are numerous gasoline or diesel engine-driven types which don't rely
on electrical input, thus shielded metal arc welding can be accomplished in remote
locations. Also, some of the newer solid state power sources are so small and lightweight that the welder can easily carry them to the work. Due to the presence of
numerous types of electrodes, the process is considered quite versatile. Finally, with
the improved equipment and electrodes available today, the resulting weld quality
can be consistently high.
One of the limitations of shielded metal arc welding is its speed. The speed is
primarily hampered by the fact that the welder must periodically stop welding and
replace the consumed electrode with a new one, since they are typically only 14 or
18 inches in length. It has been replaced by other semiautomatic, mechanized and
automatic processes in many applications simply because they offer increased
productivity when compared to manual shielded metal arc welding.
Another disadvantage, which also affects productivity, is the fact that following
welding, there is a layer of solidified slag which must be removed. A further
limitation, when low hydrogen type electrodes are being utilized, is that they
require storage in an appropriate electrode holding oven which will help to maintain
their low moisture levels.
Now that some of the basic principles have been presented, it is appropriate to
discuss some of the discontinuities which may result when the shielded metal arc
process is utilized. While these are not the only discontinuities that can be expected,
they may result because of the misapplication of this particular process.
One of those problems is the presence of porosity in the finished weld. When
porosity is encountered, it is normally the result of the presence of moisture or
contamination in the weld region. It could be present in the electrode coating, on
the surface of the material, or come from the atmosphere surrounding the welding
operation. Porosity can also occur when the welder is using an arc length which is
too long. This problem of "long- arcing" is especially distressing in the case of low
hydrogen electrodes. So, the shorter arc length not only increases the amount of
heating produced, but it will also aid in the elimination of porosity in the weld metal.
Page 6 - 6
Porosity can also result from the presence of a phenomenon referred to as arc blow.
While this can occur with any arc welding process, it will be discussed here since it is
a common problem which plagues the manual welder.
To understand arc blow, one must first know that there is a magnetic field
developed whenever an electric current is passed through some conductor. This
magnetic field is developed in a direction perpendicular to the direction of the
electric current, so it can be visualized as a series of concentric circles surrounding
the conductor.
This magnetic field is strongest when contained entirely within a magnetic material
and resists having to travel through the air outside this magnetic material.
Consequently, when welding some magnetic material, such as steel, the field can
become distorted when the arc approaches the edge of a plate, the end of a weld or
some abrupt change in contour of the part being welded
To reduce the effects of arc blow, several techniques can be attempted. They
include:
1.
2.
3
4.
5.
6.
7.
8.
9.
10.
Change from DC to AC.
Hold as short of an arc as possible.
Reduce welding current.
Angle the electrode in the direction opposite the arc blow.
Use heavy tack welds at either end of a joint, with
intermittent tack welds along length of joint.
Weld toward a heavy tack or toward a completed weld.
Use a back-step technique.
Weld away from the ground to reduce back blow; weld
toward the ground to reduce forward blow.
Wrap ground cable around the workpiece and pass ground
current through it in such a direction that the magnetic field
set up will tend to neutralize the magnetic field causing the
arc blow.
Extend the end of the joint by attaching runoff plates.
In addition to porosity, arc blow can also cause: spatter, undercut, improper weld
contour, and decreased penetration.
Slag inclusions could also occur with SMAW simply because it relies on a flux system
for weld protection. With any process utilizing flux, the possibility of trapping slag
within the weld deposit is a definite concern. The welder can reduce this tendency
by using techniques which allow the molten slag to flow freely to the surface of the
metal. Thorough cleaning of the slag from each weld pass prior to deposition of
additional passes will also reduce the occurrence of slag inclusions in multipass
welds.
Since shielded metal arc welding is primarily accomplished manually, numerous
discontinuities can result from improper manipulation of the electrode. Some of
these flaws are: incomplete fusion, incomplete penetration, cracking, undercut,
overlap, incorrect weld size, and improper weld profile.
Page 6 - 7
Gas Metal Arc Welding (GMAW)
The next process to be discussed here is gas metal arc welding. While gas metal arc
welding is the AWS designation for the process, it is also commonly referred to as
"MIG" welding. It is most commonly employed as a semiautomatic process;
however, it lends itself well to mechanized and automatic applications as well.
Therefore, it finds itself well suited for robotic welding applications. Gas metal arc
welding is characterized by a solid wire electrode which is fed continuously through
a welding gun. An arc is created between this wire and the workpiece to heat the
base and filler materials. Once molten, the wire becomes deposited in the weld joint
An important feature here is the fact that all of the shielding for welding is provided
by a protective gas atmosphere which is also emitted from the welding gun from
some external source. Gases used include both inert and reactive types. Inert gases
such as argon and helium are used for some applications. They can be applied
singly, or in combination with each other or mixed with some type of reactive gas
such as oxygen or carbon dioxide. Many gas metal arc welding applications utilize
carbon dioxide shielding alone, because of its relatively low cost compared to inert
gases.
The electrodes used for this process are solid wires which are supplied on spools or
reels of various sizes. As is the case for shielded metal arc welding electrodes, there
is an approved American Welding Society identification system for gas metal arc
welding electrodes. They are denoted by the letters "ER," followed by two or three
numbers, the letter "S," a hyphen, and finally another number.
"ER" designates the wire as being both an electrode and a rod, meaning that it may
conduct electricity or simply be applied as a filler metal when used with other
welding processes. The next two or three numbers state the minimum tensile
strength of the deposited weld metal in thousands of pounds per square inch. So,
like the SMAW types, a "70" denotes a filler metal whose tensile strength is at least
70,000 psi. The letter "S" stands for a solid wire. Finally, the number after the
hyphen refers to the particular chemistry of the electrode. This will dictate both its
operating characteristics as well as what properties are to be expected from the
deposited weld. Gas metal arc electrodes typically have increased amounts of
deoxidizers such as manganese, silicon and aluminum to assist the shielding gas in
the protection of the molten weld metal.
Even though the wire doesn't have a flux coating, it is still important to properly
store the material when not in use. The most critical factor here is that the wire
must be kept clean. If allowed to remain out in the open, it may become
contaminated with rust, oil, moisture, grinding dust or other elements present in a
weld shop environment. So, when idle, the wire should be kept in its original plastic
wrapping and/or shipping container. Even when a spool of wire is in place on the
wire feeder, it should be covered with some protective covering when not used for
prolonged periods of time.
The power supply utilized for gas metal arc welding is quite different from the type
employed for shielded metal arc welding. Instead of a constant current type, gas
Page 6 - 8
metal arc welding uses what is referred to as a constant voltage, or constant
potential, power source. That is, welding is accomplished using a preset value of
voltage over the a range of welding currents.
Gas metal arc welding is normally accomplished using direct current, electrode
positive. When this type of power source is combined with a wire feeder the result
is a welding process which can be either semiautomatic, mechanized or fully
automatic. This reduces the degree of skill required to perform gas metal arc
welding.
The equipment is more complex than that used for shielded metal arc welding. A
complete setup includes a power source, wire feeder, gas source, and welding gun
attached to the wire feeder by a flexible cable through which the electrode and gas
travel. To set up for welding, the welder will adjust the voltage at the power source
and the wire feed speed at the wire feeder. As the wire feed speed is increased, the
welding current increases as well. The melt-off rate of the electrode is proportional
to the arc current, so the wire feed speed actually controls this feature as well.
It was mentioned that this power source is a constant potential type; however, a
look at a typical V-A curve will show that the line is not flat but actually has a slight
slope.
This feature allows the process to function as a semi-automatic type, meaning that
the welder does not have to control the feeding of the filler metal as was the case for
manual shielded metal arc welding. Another way to describe this system is to call it
a "Self-Regulating Constant Potential" system.
This is accomplished by the fact that a minor change in the actual arc voltage (caused
by a variation in the gun's position with respect to the workpiece) will result in a
substantial increase or decrease in the arc current.
It can be seen that a decrease in arc voltage (gun moved closer to the workpiece)
will produce an instantaneous increase in current. This in turn results in an increase
in the electrode melt-off rate which instantaneously burns off additional electrode to
bring the arc voltage (length) back to its preset value. Similarly, an increase in the
arc voltage (gun moved away from the workpiece) will decrease the current and
therefore the electrode melt-off rate. The wire continues to be fed at its preset rate
to again provide the original value of arc voltage.
This reduces the effect of the operator's manipulation on the welding characteristics,
to make the process less operator- sensitive and therefore easier to learn.
When the machine adjustments are changed, the result is that the operating
characteristics will be drastically altered. Of primary concern is the manner in which
the molten metal is transferred from the end of the electrode, across the arc region,
to the base metal. With gas metal arc welding, there are four basic modes of metal
transfer. They are: spray, globular, pulsed arc, and short circuiting. Their
characteristics are so different that it's almost as if there are four separate welding
processes. Each specific type has definite advantages and limitations which make it
better for some applications than others. The type of metal transfer depends upon
Page 6 - 9
several factors, including: shielding gas, current and voltage levels and power
supply characteristics.
One of the basic ways in which these four types differ is that they provide varying
amounts of heat to the workpiece. Spray transfer is considered to be the hottest,
followed by globular, pulsed arc and finally short circuiting. Therefore, spray
transfer is the best for heavier sections and full penetration weld joints, as long as
they can be positioned in the flat position.
Globular transfer provides almost as much heating and weld metal deposition, but
its operating characteristics tend to be less stable, resulting in increased spatter.
Pulsed arc gas metal arc welding requires a welding power source capable of
producing a pulsing direct current output which allows the welder to program the
exact combination of high and low currents for improved heat control and process
flexibility. The welder can set both the amount and duration of the high current
pulse. So during operation, the current alternates between a high pulse current and
a lower pulse current, both of which can be set with machine controls.
Short circuiting transfer results in the least amount of heating to the base metal,
making it an excellent choice for welding of sheet metal and joints having excessive
gaps due to poor fitup.
Short circuiting transfer is characteristically colder due to the fact that the electrode
actually comes in contact with the base metal creating a short circuit for a portion of
the welding cycle. So, the arc is intermittently operating and extinguishing. The
brief periods of arc extinction allow for some cooling to occur to aid in reducing the
tendency of burning through thin materials. Care must be taken when short
circuiting transfer is used for heavy section welding, since incomplete fusion could
result from insufficient heating of the base metal.
As mentioned, the shielding gases have a significant effect on the type of metal
transfer. Spray transfer can be achieved only when there is at least 80% argon
present in the gas mixture. CO2 is probably the most popular gas for GMAW of
carbon steel, primarily due to its relatively low cost and its excellent penetration
characteristics. One drawback which must be realized, however, is that there will be
more spatter which may require removal, reducing the overall efficiency.
The versatility offered by this process has resulted in its utilization in many
industrial applications. GMAW can be effectively used to join or overlay many
types of ferrous and nonferrous metals. The use of gas shielding instead of some
type of flux reduces the possibility of introducing hydrogen into the weld zone, so
GMAW can be used successfully in situations where the presence of hydrogen could
cause problems.
Due to the lack of a slag coating which must be removed after welding, GMAW is
well suited for automatic and robotic welding or other high production situations.
This is one of the major advantages of the process. Since there is little or no cleaning
following welding, the overall efficiency is greatly improved. This efficiency is
further increased by the fact that the continuous roll of wire doesn't require
changing as often as the individual electrodes used in SMAW. All of this increases
the amount of time in which actual production welding can be accomplished.
Page 6 - 10
Another benefit of gas metal arc welding is that it is a relatively clean process,
primarily due to the fact that there is no flux present. Shops with ventilation
problems can find some relief by switching to gas metal arc welding instead of
shielded metal arc welding or flux cored arc welding, because less smoke is
generated. With the presence of numerous types of electrodes and equipment
which has become more portable, the versatility of gas metal arc welding continues
to improve. One additional benefit relates to the visibility of the process. Since no
slag is present, the welder can more readily observe the action of the arc and molten
puddle to improve control.
While the use of shielding gas instead of flux does provide some benefits, it can also
be thought of as a limitation, since this is the primary way in which the molten metal
is protected and cleaned during welding. If the base metal is excessively
contaminated, the shielding gas alone may not be sufficient to prevent the
occurrence of porosity. GMAW is also very sensitive to drafts or wind which tend
to blow the shielding gas away and leave the metal unprotected. For this reason,
gas metal arc welding is not well suited for field welding.
It is important to realize that simply increasing the gas flow rate above
recommended limits will not necessarily guarantee that adequate shielding will be
provided. In fact, high flow rates may tend to increase the possibility of porosity
because these increased flow rates may actually draw atmospheric gases into the
weld zone.
Another disadvantage is that the equipment required is more complex than that
used for shielded metal arc welding. This increases the possibility that some
mechanical problem could cause weld quality problems. Such things as worn gun
liners and contact tips can alter the feeding and electrical characteristics to the point
that defective welds could be produced.
The primary inherent problems have already been explored somewhat. They are:
porosity due to contamination or loss of shielding, incomplete fusion due to the use
of short circuiting transfer on heavy sections, and arc instability caused by worn
liners and contact tips. Although such problems could be disastrous, they can be
alleviated if certain precautions are taken.
To reduce the possibility of porosity, parts should be cleaned prior to welding and
the weld zone protected from any excessive wind using enclosures or windbreaks.
If porosity persists, the gas should be checked to assure that there is no moisture
present.
The problem of incomplete fusion is a real one when we talk about GMAW,
especially when short circuiting transfer is being used. This is due in part to the fact
that this is a "open arc" process since no flux is used. Without this layer of shielding
from the arc, the increased intensity of the arc makes the welder believe that there is
a tremendous amount of heating of the base metal. Such a feeling could be very
deceiving, so the welder must be aware of the limitation and assure that the arc is
being directed where the metal is to be fused.
Page 6 - 11
Finally, equipment should be well maintained to alleviate the problems associated
with unstable wire feeding. Each time a roll of wire is replaced, the liner should be
blown out with compressed air to remove particles which could cause jamming. If
the problem persists, the liner should be replaced. The contact tip should be
changed periodically as well. When it becomes worn, the point of electrical contact
changes so that the electrical stickout is increased without the welder knowing it.
The electrical stickout is also referred to as the contact tube-to-work distance.
Flux Cored Arc Welding (FCAW)
The next process to be described is flux cored arc welding. This is very similar to gas
metal arc welding except that the electrode is tubular and contains a granular flux
instead of the solid wire used for gas metal arc welding
It shows the tubular electrode being fed through the contact tip of the welding gun
to produce an arc between the electrode and the workpiece. With flux cored arc
welding, there may or may not be a shielding gas, depending upon what type of
electrode is utilized. Some are designed to provide all of the necessary shielding
from the internal flux, while others require additional shielding from an auxiliary
shielding gas. As the welding progresses, a bead of solidified weld metal is
deposited. Covering this solidified weld metal is a layer of slag, as was the case for
shielded metal arc welding.
With FCAW, as with other processes, there is a system for identification of the
various types of welding electrodes.
An identification begins with the letter "E" which stands for electrode. The next
number refers to the minimum tensile strength of the deposited weld metal in ten
thousands of pounds per square inch, so a "7" means that the weld metal strength is
at least 70,000 psi. The next digit is either a "0" or "1". A "0" means that the electrode
is suitable for use in the flat or horizontal fillet positions only, while a "1" describes
an electrode which can be used in any position. Following these numbers is the
letter "T" which refers to a tubular electrode. This is followed by a hyphen and then
another number which denotes the particular grouping based upon chemical
composition of deposited weld metal, type of current, polarity of operation,
whether it requires a shielding gas, and other specific information for the category.
With this identification system, it can be determined whether or not a certain
classification of electrode requires an auxiliary shielding gas. This is important to the
welding inspector since flux cored arc welding can be performed with or without an
external shielding gas.
Some electrodes are formulated to be used without any additional shielding other
than that contained within the electrode. They are designated by the numbers -3, -4,
-6, -7, and -8. However, those electrodes having the numerical suffixes -1, -2 or -5
require some external shielding to aid in protecting the molten metal. Both types
offer advantages, depending upon the application.
For example, the self-shielded types are better suited for field welding where wind
could result in a loss of gaseous shielding. Gas shielded types are typically used
Page 6 - 12
where the need for superior weld metal properties warrants the additional cost.
Gases typically used for flux cored arc welding are CO2 or 75% Argon - 25% CO2.
The equipment utilized for FCAW is essentially identical to that for GMAW.
Some exceptions might be higher current capacity guns and power sources, lack of
gas apparatus for self-shielded electrodes, and knurled wire feed rolls. Like GMAW,
FCAW utilizes a constant voltage direct current power supply. Depending on the
type of electrode, the operation may be DCEP (- 1, -2, -3, -4, -5, -6, and -8) or DCEN
(-7).
The flux cored arc welding process is a relatively new method compared to other
welding processes. Its relatively good performance on contaminated surfaces and
the increased deposition rates offered have helped flux cored arc welding to replace
SMAW and GMAW for many applications. The process is utilized in all industries
where the predominant materials are ferrous. It can be used with satisfactory
results for both shop and field applications.
Although the majority of the electrodes produced are ferrous (for both carbon and
stainless steels) some nonferrous ones are available as well. Some of the stainless
types actually employ a carbon steel sheath surrounding the internal flux which also
contains granular alloying elements such as chromium and nickel.
FCAW has gained wide acceptance because of the many advantages it offers.
Probably the most significant advantage is that it provides a high efficiency in terms
of the amount of weld metal that can be deposited in a given period of time. It is
among the highest for a hand-held process. This is aided by the fact that the
electrode comes on continuous reels which increases the "arc time" just as with gas
metal arc welding. The process is also characterized by an aggressive, deeply
penetrating arc which tends to reduce the possibility of fusion-type discontinuities.
Since it is typically utilized as a semi-automatic process, the skill required for
operation is less than would be the case for a manual process. With the presence of
a flux, whether assisted by a gaseous shield or not, FCAW is capable of tolerating a
greater degree of base metal contamination than is GMAW. For this same reason,
FCAW lends itself well to field situations where the loss of shielding gas due to
winds would greatly hamper GMAW quality.
It is important to realize that this process does have certain limitations of which the
inspector should be aware. First, since there is a flux present, there is a layer of
solidified slag which must be removed before depositing additional layers of weld
or before a visual inspection can be made.
Due to the presence of this flux, there is a significant amount of smoke generated
during welding. Prolonged exposure in unvented areas could prove to be
unhealthy for the welder. This smoke also reduces the welder's visibility to the
point where it may be difficult to properly manipulate the arc in the joint. Although
smoke extractor systems are available, they tend to add bulk to the gun which
increases the weight and decreases visibility. They also may disturb the shielding if
an auxiliary gas is being used.
Page 6 - 13
Even though FCAW is considered to be a smoky process, it is not as bad as SMAW
in terms of the amount of smoke generated for a given amount of deposited weld
metal. The equipment required for FCAW is more extensive than that for SMAW so
the initial cost and the possibility of machinery problems does limit its acceptability
for some situations.
As with any of the processes, FCAW does have some inherent problems. The first
has to do with the flux. Due to its presence there exists a possibility that the
solidified slag could become trapped in the finished weld. This could be due to
either improper interpass cleaning or improper technique.
With FCAW, it is critical that the welder travels fast enough so that the arc is always
on the leading edge of the molten puddle. When the travel speed is slow enough to
allow the arc to be toward the middle or back of the puddle, molten slag may roll
ahead of the puddle and become trapped. Another inherent problem involves wire
feeding apparatus. As was the case for GMAW, lack of maintenance could cause
wire feeding problems which may affect the quality of the weld.
Gas Tungsten Arc Welding (GTAW)
The next process to be discussed is gas tungsten arc welding which has several
interesting differences when compared to those already explained.
The most significant feature here is that the electrode used is not intended to be
consumed during the welding operation. It is made of pure or alloyed tungsten
which has the ability to withstand very high temperatures, even those of the
welding arc. Therefore, when current is flowing, there is an arc created between the
tungsten electrode and the workpiece. If any filler metal is required, it must be
added externally, either by hand or with the use of some mechanical wire feed
system. All of the arc and metal shielding is achieved through the use of an inert gas
which flows out of the nozzle surrounding the tungsten electrode. The deposited
weld bead has no slag requiring removal because no flux is utilized.
As with the other processes, there is a system whereby the various types of
tungsten electrodes can be easily identified. The designations consist of a series of
letters starting with an "E" which stands for electrode. Next comes a "W" which is
the chemical abbreviation for tungsten. These letters are followed by letters and
numbers which describe the alloy type. Since there are only five different
classifications, they are more commonly differentiated using a color code system.
The table below shows the classifications and the appropriate color code.
AWS Tungsten Electrode Classifications
AWS Classification Alloy Color
EWP Pure tungsten Green
EWTh-1 0.8-1.2% thoria Yellow
EWTh-2 1.7-2.2% thoria Red
EWTh-3 0.35-0.55% thoria Blue
EWZr 0.15-0.40% zirconia Brown
Page 6 - 14
The presence of the thoria or zirconia aid in improving the electrical characteristics,
by making the tungsten slightly more emissive. This simply means that it is easier
to initiate an arc with these thoriated or zirconated types than is the case for pure
tungsten electrodes. Pure tungsten is quite often utilized for the welding of
aluminum because of its ability to form a ball when heated. With a ball instead of a
point, there is a lower concentration of current which reduces the possibility of
damaging the tungsten. The EWTh-2 type is most commonly used for the joining of
ferrous materials.
GTAW can be performed using DCEP, DCEN or AC. The DCEP will result in more
heating of the electrode, while the DCEN will tend to heat the base metal more. AC
alternately heats the electrode and base metal. AC is typically used for the welding
of aluminum because the alternating current will increase the cleaning action to
improve weld quality. DCEN is most commonly used for the welding of steels.
As mentioned, GTAW utilizes inert gases for shielding. Inert means that the gases
will not combine with the metal, but will protect it from contaminants. Argon and
helium are the two most commonly used inert gases, based on their relative costs
and availability compared to other types of inert gases. Some mechanized stainless
steel welding applications utilize a shielding gas consisting of argon and a small
amount of hydrogen, but this represents a very minor portion of the gas tungsten
arc welding which is performed.
The equipment required for GTAW has as its primary element a power source like
the one used for SMAW; that is, a constant current type. Since there is a gas present,
it is now necessary to have apparatus for its control and transmission.
An added feature of this welding system, which is not shown, is a high frequency
generator which aids in the initiation of the welding arc. In order to alter the
welding heat during the welding operation, a remote current control may also be
attached. It can be foot-operated or controlled by some device mounted on the
torch itself. This is particularly useful for welding thin materials and open root pipe
joints, where instantaneous control is necessary.
There are numerous applications for GTAW in many industries. It is capable of
welding virtually all materials, because the electrode is not melted during the
welding operation. Its ability to weld at extremely low currents makes gas tungsten
arc welding suitable for use on the thinnest (down to 0.005 inch) of metals. Its
typically clean and controllable operation causes it to be the perfect choice for
extremely critical applications such as those found in the aerospace, food and drug
processing, and power piping industries.
The principal advantage of GTAW lies in the fact that it can produce welds of high
quality and excellent visual appearance. Also, since no flux is utilized, the process is
quite clean; plus there is no slag to remove after welding. As mentioned before,
extremely thin sections can be welded. Due to the nature of its operation, it is
suitable for welding most metals, many of which are not readily weldable using
other welding processes. If joint design permits, these materials can be welded
without the use of additional filler metal. When required, numerous types of filler
metals exist in wire form for a wide range of metal alloys. In the case where there is
Page 6 - 15
no commercially-available wire for a particular metal alloy, it is possible to produce
a suitable filler metal by simply shearing a piece of identical base metal to produce a
narrow piece which can be hand-fed into the weld zone just as if it were a wire.
Contrasting these advantages are several disadvantages. First, GTAW is among the
slowest of the available welding processes. While it produces a clean weld deposit, it
is also characterized as having a low tolerance for contamination. Therefore, base
and filler metals must be extremely clean prior to welding. When utilized as a
manual process, Gas tungsten arc welding requires a high skill level. This is partially
due to the need for two hands--one to manipulate the torch and one to feed the filler
metal. GTAW is normally selected in situations where the need for high quality
warrants additional cost to overcome these limitations.
One of the inherent problems associated with this method has to do with its inability
to tolerate contamination. If contamination or moisture is encountered, whether
from the base metal, filler metal or shielding gas, the result could be porosity in the
deposited weld. When porosity is noted, this is a sign that the process is out of
control and some preventive measures are necessary. Checks should be made to
determine the source of the contamination so that it can be eliminated.
Another inherent problem which is almost totally confined to the GTAW process is
that of tungsten inclusions. As the name implies, this discontinuity occurs when
pieces of the tungsten electrode become included in the weld deposit.
Tungsten inclusions can occur due to a number of reasons, including:
1.
2.
3.
4.
5.
6
7.
8.
9.
10.
Contact of electrode tip with molten metal;
Contact of filler metal with hot tip of electrode;
Contamination of the electrode tip by spatter;
Exceeding the current limit for a given electrode diameter or
type;
Extension of electrodes beyond their normal distances from
the collet, resulting in overheating of the electrode;
inadequate tightening of the collet;
inadequate shielding gas flow rates or excessive wind drafts
resulting in oxidation of the electrode tip;
defects such as splits or cracks in the electrode;
use of improper shielding gases; and
improper grinding of the electrode tip.
Submerged Arc Welding (SAW)
The last of the more common welding processes to be discussed is submerged arc
welding. This method is typically the most efficient one mentioned so far in terms
of the rate of weld metal deposition. SAW is characterized by the use of a
continuously-fed solid wire electrode which provides an arc that is totally covered
by a layer of granular flux, hence the name "submerged" arc.
As mentioned, the wire is fed into the weld zone much the same way as with gas
metal arc welding or flux cored arc welding. The major difference, however, is in
Page 6 - 16
the method of shielding. With submerged arc welding, a granular flux is poured
ahead of or around this wire electrode to facilitate the protection of the molten
metal. As the welding progresses, in addition to the weld bead, there is a layer of
slag and still granular flux covering the solidified weld metal. The slag must be
removed and discarded. However, the granular flux can be recovered and reused if
care is taken to prevent its contamination. In some cases where the flux must
provide alloying for the weld, reuse of the flux may not be advisable.
Since SAW utilizes a separate electrode and flux, there are numerous combinations
available for specific applications. There are two general types of combinations
which can be used to provide an alloyed weld deposit: an alloy electrode with a
neutral flux or a mild steel electrode with an alloy flux. Therefore, to properly
describe the filler material for Submerged Arc Welding, the American Welding
Society identification system consists of designations for both the electrode and flux.
The equipment used for submerged arc welding consists of several components.
Since this process can be utilized as a fully mechanized or semiautomatic method,
the equipment used for each is slightly different. In either case, however, some
power source is required. Although most submerged arc welding is performed
with a constant voltage power source, there are certain applications where a
constant current type is preferred. As with gas metal arc welding and flux cored arc
welding, a wire feeder forces the wire through the cable liner to the welding torch.
The flux must be moved to the weld zone somehow. For mechanized systems, the
flux is generally poured into a hopper above the welding torch and fed by gravity
so that it pours either slightly ahead of the arc or around the arc from a nozzle
surrounding the contact tip. In the case of semiautomatic submerged arc welding,
the flux is forced to the gun using compressed air which makes the granular flux
behave similar to a liquid or there is a hopper connected directly to the hand-held
gun.
Another equipment variation is the choice of alternating or direct current, either
polarity. The type of welding current will affect both penetration and weld bead
contour. For some applications multiple electrodes can be utilized. The electrodes
may be energized by a single power source, or multiple power sources may be
necessary. The use of multiple electrodes provides even more versatility for the
process.
SAW has found acceptance in many industries, and it can be performed on
numerous metals. Due to the high rate of weld metal deposition, it has shown to be
quite effective for overlaying or building up material surfaces. In situations where a
surface needs improved corrosion or wear resistance, it is often more economical to
cover a susceptible base metal with a resistant weld overlay. If this application can
be mechanized, submerged arc welding is an excellent choice.
Probably the biggest advantage of SAW is its high deposition rate. It can typically
deposit weld metal more efficiently than any of the more common processes. The
submerged arc welding process also has high operator appeal, first because of the
lack of a visible arc which allows the operator to control the welding without the
need for a filter lens and other heavy protective clothing. The other beneficial
Page 6 - 17
feature is that there is less smoke generated than with some of the other processes.
Another feature of the process which makes it desirable for many applications is its
ability to penetrate deeply.
The major limitation of SAW is that it can only be done in a position where the flux
can be supported in the weld joint. When welding in a position other than the flat or
horizontal fillet positions, some device is required to hold the flux in place so it can
perform its job. Another limitation is that, like most mechanized processes, there
may be a need for extensive fixturing and positioning equipment. As with other
processes using a flux, finished welds have a layer of solidified slag which must be
removed.
If welding parameters are improper, weld contours could be such that this job of
slag removal is even more difficult. The final disadvantage relates to the flux which
covers the arc during welding. While it does a good job of protecting the welder
from the arc, it also prevents him from seeing exactly where the arc is positioned
with respect to the joint. With a mechanized setup, it is advisable to track the entire
length of the joint without the arc or the flux to check for alignment. If the arc is not
properly directed, incomplete fusion could result.
There are some inherent problems related to SAW. The first has to do with the
granular flux. Just as with low hydrogen SMAW electrodes, it is necessary to protect
the submerged arc welding flux from moisture. It may be necessary to store the
flux in heated containers prior to use. If the flux becomes wet, porosity and
underbead cracking may result.
Another characteristic problem of SAW is solidification cracking. This results when
the welding conditions provide a weld bead having an extreme width-to-depth
ratio. That is, if the bead's width is much greater than its depth, or vice versa,
centerline shrinkage cracking could occur during solidification.
Plasma Arc Welding (PAW)
The next process to be explained is plasma arc welding. A plasma is defined as an
ionized gas. With any process utilizing an arc, a plasma is created. However, PAW
is so named because of the intensity of this plasma region. At first glance, PAW
could be easily mistaken for GTAW because the equipment required is quite similar.
The two processes utilize the same type of power source. However when we look
closely at the torch itself the difference becomes more obvious.
Both the PAW and GTAW torches utilize a tungsten electrode for the creation of the
arc. However, with the PAW torch, there is a copper orifice within the ceramic
nozzle. There is a high velocity "plasma" gas which is forced through this orifice and
past the welding arc resulting in the constriction of the arc.
This constriction, or squeezing, of the arc causes it to be more concentrated, and
therefore more intense. One way to illustrate the difference in arc intensity between
GTAW and PAW would be to use the analogy of an adjustable water hose nozzle.
The GTAW arc would be comparable to the gentle mist setting, while the PAW arc
Page 6 - 18
would behave more like the setting which provides a concentrated stream of water
having a greater force.
There are two general categories of plasma arc operation, namely the transferred
and the nontransferred arc.
With the transferred arc, the arc is created between the tungsten electrode and the
workpiece. The nontransferred arc, on the other hand, occurs between the tungsten
electrode and the copper orifice. The transferred type arc is generally utilized for
both welding and cutting of conductive materials, because it results in the greatest
amount of heating of the workpiece. The nontransferred type arc is preferred for
the cutting of nonconductive materials and for welding of materials when the
amount of heating of the workpiece must be minimized.
The similarities between GTAW and PAW extend to the equipment as well. The
power sources are identical in most respects. However, there are some additional
elements necessary, including: plasma control console and a source of plasma gas.
The torch, as discussed above, does differ slightly; however, a careful check of the
internal configuration must be made to be certain.
As indicated, two separate gases are required: the shielding gas and the orifice (or
plasma) gas. Argon is most commonly employed for both types of gas. However,
welding of various metals might warrant the use of helium or combinations of
argon/helium or argon/hydrogen for one or the other gases.
The primary applications for PAW are similar to those for GTAW. PAW is utilized
for the same materials and thicknesses. PAW becomes the choice where
applications warrant the use of a more localized heat source. It is used extensively
for full penetration welds in material up to 1/2 inch thick by employing a technique
referred to as "keyhole welding.
Welding is performed on a square butt joint with no root opening. The
concentrated heat of the arc penetrates through the material thickness to form a
small keyhole. As welding progresses, the keyhole moves along the joint melting
the edges of the base metal which then flow together and solidify after the welding
arc passes. This creates a high quality weld, with no elaborate joint preparation and
fast travel speeds compared to GTAW.
One advantage of PAW, which was mentioned before, is that it provides a localized
heat source. This allows for faster welding speeds and therefore less distortion.
Since the standoff used between the torch end and the workpiece is typically quite
long, the welder has better visibility of the weld being made. Also, since the
tungsten electrode is recessed within the torch, the welder is less likely to stick it in
the molten metal and produce a tungsten inclusion.
The ability to use this process in a keyhole mode is also desirable. The keyhole is a
positive indication of complete penetration and weld uniformity. This weld
uniformity is in part due to the fact that plasma arc welding is less sensitive to
changes in arc length. The presence of its collimated arc will permit relatively large
changes in torch-to-work distance without any change in its melting capacity.
Page 6 - 19
PAW is limited to the effective joining of materials 1 inch or less in thickness. The
initial cost of the equipment is substantially greater than that for GTAW, primarily
because there is additional apparatus required. Finally, the use of PAW requires
greater operator skill than would be the case for GTAW.
Among the problems that may be encountered with this process are two types of
metal inclusions. Tungsten inclusions may result from high current levels; however,
the fact that the tungsten is recessed helps to prevent this occurrence. High current
could also result in the copper orifice melting and being deposited in the weld metal.
Another problem that may be encountered when keyhole welding is being done is
referred to as tunneling. This occurs when the keyhole is not completely filled at the
end of the weld, leaving a cylindrical void which may extend entirely through the
throat of the weld. When using the keyhole technique, there is also a possibility of
getting incomplete fusion since the arc and joint are so narrow. As a result, even
small amounts of mistracking can produce incomplete fusion along the joint.
Oxyacetylene Welding (OAW)
The next process is oxyacetylene welding. While the term oxyfuel welding is also
used, acetylene is the only fuel gas capable of producing high enough temperatures
for effective welding. With OAW, the energy for welding is created by a flame, so
this process is considered to be a chemical welding method. Just as the heat is
provided by a chemical reaction, the shielding for oxyacetylene welding is
accomplished by this flame as well. Therefore, no flux or external shielding is
necessary.
The equipment for oxyacetylene welding is relatively simple. It consists of several
parts: oxygen tank, acetylene tank, pressure regulators, torch, and connecting hoses.
The oxygen cylinder is a hollow high pressure container capable of withstanding a
pressure of approximately 2200 psi. The acetylene cylinder on the other hand, is
filled with a porous material similar to cement.
Acetylene exists in the cylinder dissolved in liquid acetone. Care must be taken since
gaseous acetylene is extremely unstable at pressures exceeding 15 psi and an
explosion could occur even without the presence of oxygen. Since the acetylene
cylinder contains a liquid it is important that it remains upright to prevent spillage.
Each cylinder has attached to its top a pressure regulator which reduces the high
internal tank pressure to working pressures. Hoses then connect these regulators to
the torch. The torch includes a mixing section where the oxygen and acetylene
combine to provide the necessary mixture. The ratio of these two gases can be
altered by the adjustment of two separate control valves. Normally, for carbon
steel welding, they are adjusted to provide a mixture, which is referred to as a
neutral flame. A higher amount of oxygen will create an oxidizing flame and a
higher amount of acetylene will produce a carburizing flame. After the gases are
mixed they flow through a detachable tip. Tips are made in a variety of sizes to
allow welding of different metal thicknesses.
Page 6 - 20
The filler material used for OAW on steel has a simple identification system. Two
examples are RG-45 and RG-60. The "R" designates it as a rod, "G" stands for gas and
the 45 and 60 relate to the minimum tensile strength of the weld deposit in
thousands of pounds per square inch (psi). So 45 designates a weld deposit having a
tensile strength of at least 45,000 psi.
Although not utilized as extensively as it once was, OAW still sees some usage. Its
primary tasks include the welding of thin steel sheet and small diameter steel piping.
It is also applied in many maintenance situations as well.
The advantages of OAW include some desirable features of the equipment itself.
First, it is relatively inexpensive and can be made very portable. This portability
relates not only to the compact size but also to the fact that there is no electrical
input required. Care should be taken when moving the equipment so that the
valves on the cylinders are not damaged. If broken off, a cylinder can turn into a
lethal missile. So, whenever transported, the regulators should be removed and the
valves covered with special screw-on caps for protection from impact.
The process also has certain limitations. For one, the flame does not provide as
concentrated a heat source as can be achieved by an arc. Therefore, if a groove weld
is being made, the weld preparation should exhibit a thin "feather edge" to assure
that complete fusion is obtained at the root of the joint.
This lower heat concentration also results in a relatively slow process, so we
typically consider OAW best suited for thin section welding. As with any of the
welding processes requiring a second hand to feed the filler metal, OAW requires a
substantial skill level for best results.
There are certain inherent problems associated with OAW. They are primarily
related to either improper manipulation or adjustment of the flame. Since the heat
source is not concentrated, care must be taken to direct the flame properly to assure
adequate fusion. If the flame is adjusted such that an oxidizing flame or carburizing
flame is produced, weld metal properties could be degraded, so it is important to
have equipment capable of providing uniform gas flow.
Cutting Processes
So far the discussion has involved only those methods utilized for joining metals
together. Also of importance in metal fabrication are those processes utilized to cut
or remove metal. These processes are utilized prior to welding to produce proper
part shapes or make specific joint preparations. During or after welding, some of
these same processes can also be employed to remove defective areas of welds or to
produce a specific configuration if the as-welded shape is not satisfactory for the
intended purpose of the part.
Oxyfuel Cutting (OFC)
The first of these cutting processes is oxyfuel cutting. An oxyfuel flame is used to
heat the metal to a temperature at which it will readily oxidize, or burn. Once that
temperature has been achieved, a high pressure stream of cutting oxygen is directed
Page 6 - 21
on the metal's heated surface to produce an oxidation reaction. This stream of
oxygen also tends to remove the slag and oxide residue which is produced by this
oxidation reaction. Therefore, OFC can be thought of as a type of chemical cutting
process
The equipment utilized for OFC is essentially the same as that for OAW except that,
instead of a welding tip, there is now a cutting attachment which includes an
additional lever or valve to turn on the cutting oxygen.
The cutting operation also requires a special cutting tip which is attached to the end
of the torch. It consists of a series of small holes arranged in a circle around the
outside edge of the end of the cutting tip. This is where the oxyfuel gas mixture
flows to provide the preheat for cutting. Located in the center of these holes is a
single cutting oxygen passage.
It should be noted that OFC can be accomplished using several different types of
fuel gases, such as: acetylene, natural, propane, gasoline, and MAPP. Each provide
various degrees of efficiency and may require slightly modified cutting tips. Other
factors which should be considered when selecting the proper fuel gas include:
preheating time required, cutting speeds, cost, availability, amount of oxygen
required to burn gas efficiently, and ease and safety of transporting fuel containers.
Cutting is accomplished by applying heat to the part using the preheat flame which
is an oxyfuel mixture. Once the metal has been heated to its kindling temperature,
the cutting oxygen is turned on to oxidize the hot metal. The oxidation of the iron
produces a tremendous amount of heat. This chemical reaction provides the
necessary heat to rapidly melt the metal and simultaneously blow the oxidation
products from the joint. The width of the cut produced is referred to as the kerf.
The amount of offset between the cut entry and exit points, measured along the cut
edge is the drag.
Although OFC is utilized extensively by most industries, it is limited to the cutting of
carbon and low alloy steels only. As the amounts of various alloying elements
increase, one of two things can happen. Either they make the steel more difficult to
cut or they may give rise to hardened or heat-checked cut surfaces, or both
In most cases, the addition of certain amounts of alloying elements may prevent
conventional OFC. In many cases, these elements are oxidation resistant types. In
order for an oxyfuel cut to be accomplished, the metal oxide which is produced must
melt at some temperature near or below the melting point of the metal. Therefore,
in order to cut cast iron or stainless steel with this process, special techniques
involving additional equipment are necessary. These techniques include: torch
oscillation, use of waster plate, wire feeding, powder cutting, and flux cutting.
OFC's advantages include its relatively inexpensive and portable equipment making
it feasible for use in both shop and field applications. Cuts can be made on thin or
thick sections. Steels up to five feet thick have been cut using this process. When
mechanized, OFC can produce cuts of reasonable accuracy. When compared to
mechanical cutting methods, oxyfuel cutting of steels is more economical. To
improve this efficiency even more, multiple torch systems or stack cutting can be
utilized to cut several parts at once.
Page 6 - 22
One of the limitations of OFC is that the finished cut may require additional cleaning
or grinding to prepare it for welding. Another important limitation is that since it
utilizes heat, there may be a heat affected zone produced which could exhibit very
high hardness. This is especially important if there is a need for machining of this
surface. Employment of preheat and postheat will aid in the alleviation of this
problem. Also, even though cuts can be reasonably accurate, they still don't
compare to the accuracy possible from other mechanical cutting methods. Finally,
the flame and hot slag produced result in safety hazards for personnel near the
cutting operation.
Air Carbon Arc Cutting (CAC-A)
Another very effective cutting process is air carbon arc cutting. This process utilizes
a carbon electrode to create an arc for heating along with a high pressure stream of
compressed air to mechanically remove the molten metal.
The equipment utilized for CAC-A consists of a special electrode holder which is
attached to a constant current power source and a compressed air supply. This
special holder grasps the carbon electrode in small copper jaws, one of which has a
series of holes through which the compressed air passes. To achieve a cut, the
carbon electrode is brought close to the work to create an arc. Once the arc melts
the metal, the stream of compressed air blows away the molten metal to produce a
gouge or cut.
The electrode holder is attached to some power source as well as a source of
compressed air. Any nonflammable compressed gas could be utilized, but
compressed air is by far the least expensive, if available.
CAC-A has applications in most industries, especially since it works on any material
which conducts electricity. Even though it will cut all metals, there may be a
requirement for a particular type of electric current and polarity.
While we tend to think of its application to remove defective areas of the weld or
base metal, it is important to realize that it can be utilized quite effectively as a weld
joint preparation tool. For example, two pieces to be butt welded can be aligned
with their square-cut edges touching. The CAC-A process can then be employed to
produce a uniform U-groove preparation. CAC-A is also used for rough machining
of large, complex parts.
One of the basic advantages of CAC-A is that it is a relatively efficient method for
removal of metal. It also has the ability to cut most types of metals. Since it utilizes
the same power sources as those used for some types of welding, the equipment
costs are minimal. All that is necessary is the purchase of the special electrode
holder which is attached to an existing power source and a compressed air supply.
The primary disadvantage of the process is safety-related. It is inherently a very
noisy and dirty process. Therefore, the operator may elect to use ear protection to
reduce the noise level and breathing filters to eliminate the inhaling of the metal
Page 6 - 23
particles produced. Another limitation is that the finished cut may require some
cleanup prior to additional welding.
Plasma Arc Cutting (PAC)
The final thermal cutting method for discussion is plasma arc cutting. This process is
similar in most respects to PAW except that now the purpose is to remove metal
rather than join pieces together. The equipment requirements are similar except
that the power utilized may be much higher than that used for welding. The
transferred arc type torch is utilized because of the increased heating of the base
metal.
For mechanized cutting, not only is the torch water-cooled internally, but the actual
cutting may take place beneath a water layer to reduce noise and particulate levels.
Its primary application is for the cutting of stainless steels since they cannot be cut
effectively by oxyfuel cutting. PAC is also useful for the cutting of carbon steels;
however, it may not be economical unless the increased cutting speeds will justify
the higher initial cost.
The advantages include: the ability to cut metals which cannot be cut with OFC, the
resulting high quality cut, and increased cutting speeds for carbon steel.
One limitation is that the kerf is generally quite large and the cut edges may not be
square. Special techniques, such as water injection, can be used to improve this edge
configuration if desired. Another limitation is the high cost of equipment as
compared to oxyfuel cutting.
Mechanical Cutting
Finally, we should briefly mention some of the mechanical cutting methods utilized
in conjunction with welding. These methods include, but are not limited to:
shearing, sawing, grinding, milling, turning, shaping, drilling, planing, and chipping.
These various methods are used for: joint preparation, weld contouring, cutting of
parts to be joined, surface cleaning, and removal of defective welds.
As a welding inspector, it is important to understand how these methods are used,
as their misapplication may have a degrading effect of the final weld quality. For
example, many of these methods employ some type of cutting fluid to aid the
machining operation. If these fluids are not completely removed from the weld
surfaces, problems such as porosity and cracking may result.
Page 6 - 24
Summary
There are numerous joining and cutting processes which can be used in metal
fabrication. The welding inspector can more effectively perform the job if the
individual has an understanding of the fundamentals of these various processes.
With this knowledge, the welding inspector can spot problems before or when they
occur so correction becomes more economical. The information provided in this
discussion should give the welding inspector a basis upon which can be built to
achieve some level of understanding of welding and cutting processes. This
technical basis combined with information gained through practical experience will
allow the welding inspector to be better prepared to perform visual inspection of
welds.
Page 6 - 25
API 570 Welding Processes Quiz
1.
What welding process is pictured?
a.
GTAW
b.
FCAW
c.
SMAW
d.
SAW
2.
What welding process is pictured?
a.
GTAW
b.
FCAW
c.
SMAW
d.
GMAW
3.
What welding process is pictured?
a.
GTAW
b.
FCAW
c.
SAW
d.
GMAW
Page 6 - 26
4.
What welding process is pictured?
a.
GTAW
b.
FCAW
c.
SAW
d.
GMAW
5.
In the SMAW electrode identification system, a "1" in the third position
would mean:
a.
AC & DCEN
b.
digging arc with deep penetration
c.
all position electrode
d.
both a and b
e.
none of the above
6.
The electrode coating does which of the following:
a.
acts as a shielding
b.
acts as a deoxidation agent
c.
acts as an alloying and ionizing agent
d.
all of the above
7.
GMAW is characterized by a ________.
a.
cut length electrode
b.
flux core electrode
c.
coated electrode
d.
solid wire electrode which is fed continuously through a welding
gun
8.
Gasses for GMAW can be:
a.
inert and reactive
b.
argon or helium for some applications
c.
inert, mixed with some type of reactive gas
d.
all of the above
9.
In the electrode identification for GMAW, what does the "S" stand for,in
the electrode ER 70S-1?
a.
Silicon
b.
Spray arc
c.
Solid wire
d.
none of the above
10.
When using GMAW, the type of metal transfer depends on:
a.
shielding gas
b.
current and voltage
c.
power supply characteristics
d.
all of the above
e.
none of the above
11.
Spray transfer is considered to be ________.
Page 6 - 27
a.
b.
c.
d.
the hottest GMAW welding type transfer
the least amount of heating to the base metal
the process with the highest deposition rate for the process
the process that is a program of exact combination of high and
low currents
12.
Globular transfer is considered to be ________.
a.
the hottest GMAW welding type transfer
b.
the least amount of heating to the base metal
c.
the process with excellent deposition rate for the process
d.
the process that is a program of exact combination of high and
low currents
13.
Pulsed arc transfer is considered to be ________.
a.
the hottest GMAW welding type transfer
b.
the least amount of heating to the base metal
c.
the process with the highest deposition rate for the process
d.
the process that is a program of exact combination of high and
low currents
14.
Short circuiting transfer is considered to be ________.
a.
the hottest GMAW welding type transfer
b.
the least amount of heating to the base metal
c.
the process with the highest deposition rate for the process
d.
the process that is a program of exact combination of high and
low currents
15.
GMAW is very sensitive to __________, which tends to leave the metal
unprotected during welding.
a.
wind or drafts which tend to blow the shielding gas away
b.
ultraviolet light waves
c.
arc lengths
d.
all of the above
e.
none of the above
16.
The ________ process has an electrode that is not intended to be
consumed during the welding operation.
a.
SMAW
b.
GMAW
c.
FCAW
d.
GTAW
e.
none of the above
17.
GTAW can be performed using which of the following polarities?
a.
DCEN
b.
DCEP
c.
AC
d.
all of the above
e.
none of the above
18.
_______ and ______ are the two most commonly used inert gasses
Page 6 - 28
for the GTAW process.
a.
CO2 and oxygen
b.
Argon and helium
c.
Acetylene and oxygen
d.
none of the above
19.
One of the problems associated with GTAW is:
a.
inability to tolerate contamination
b.
it is a slow process
c.
tungsten inclusions
d.
all of the above
e.
none of the above
20.
The ________ process is characterized by the use of a continuously- fed
solid wire electrode which provides an arc that is totally covered by a layer
of granular flux.
a.
SMAW
b.
GMAW
c.
FCAW
d.
GTAW
e.
none of the above
21.
The biggest advantage of SAW is its ________.
a.
portability
b.
ability to weld out of position
c.
high deposition rate
d.
ability to produce almost no weld defects
22.
A major problem when using the SAW process is ______.
a.
high deposition rate
b.
weld contour
c.
solidification cracking
d.
none of these
Page 6 - 29
API Welding Processes Quiz
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
c
d
a
c
c
d
d
d
c
d
a
c
d
b
a
d
d
b
d
e
c
c
Page 6 - 30
API 578
Material Verification Program for New
and Existing Alloy Piping Systems
A
AP
PII R
RP
P 557788
FFiirrsstt E
Ed
diittiioon
n –– M
Maayy,, 11999999
Summary and Notes
The notes and summary information supplied is
the thoughts and opinions of ITAC and does not
represent API Committee interpretations.
The use of “Key Phrases” is intended as a study
guide only.
Page 7 - 1
(This page intentionally left blank)
Page 7 - 2
API RP 578
First Edition - May, 1999
Material Verification Program for New and
Existing Alloy Piping Systems
Foreword
This edition of API RP 578 is a recommended practice, not a code or standard.
Key phrase “recommended practice...".
1.0
SCOPE
1.1
General
API RP 578 covers recommendations for guidelines for material and
quality assurance systems to verify the nominal composition of piping.
1.3
Roles and Responsibilities
This section lists the responsibilities and players for implementing a
material verification program.
Key phrase “responsibilities”.
2
REFERENCES
Page 7 - 3
3
DEFINITIONS
(For the purposes of this standard, the following definitions apply.)
3.1 alloy material: Any metallic
material (including welding filler
materials) that contains alloying
elements such as chromium, nickel, or
molybdenum, which are intentionally
added to enhance mechanical or
physical properties and/or corrosion
resistance.
3.2 distributor: A warehousing
supplier for one or more
manufacturers or suppliers of alloy
materials or components.
3.3 fabricator: One who fabricates
piping systems or portions of a piping
system as defined by ASME B 31.3.
3.4 inspection lot: A group of items
or materials of the same type from a
common source from which a sample
is to be drawn for examination. An
inspection lot does not include items
from more than one heat.
3.5 Level of examination: The
specified percentage of the number of
components (or weldments when
specified) to be examined in an
inspection lot.
3.6 lot size: The number of items
available in the inspection lot at the
time a representative sample is
selected.
3.7 material manufacturer: An
organization that performs or
supervises and directly controls one or
more of the operations that affect the
chemical composition or mechanical
properties of a metallic material.
3.8 material nonconformance: A
positive material identification (PMI)
test result that is not consistent with
the selected or specified alloy.
3.9 material supplier: An
organization that supplies material
furnished and certified by a material
manufacturer, but does not perform
any operation intended to alter the
material properties required by the
applicable material specification.
3.10 material verification program: A
documented quality assurance
procedure used to assess metallic alloy
materials (including weldments and
attachments where specified) to verify
conformance with the selected or
specified alloy material designated by
the owner/user. This program may
include a description of methods for
alloy material testing, physical
component marking, and program
record-keeping.
3.11 mill test report: A certified
document that permits each
component to be identified according
to the original heat of material from
which it was produced and identifies
the applicable material specification
(including documentation of all test
results required by the material
specification).
3.12 owner/user: An owner or user of
piping systems who exercises control
over the operation, engineering,
inspection, repair, alteration, testing,
and rerating of those piping systems..
3.13 positive material identification
(PMI) testing: Any physical
evaluation or test of a material to
confirm that the material which has
been or will be placed into service is
consistent with the selected or
specified alloy material designated by
the owner/user. These evaluations or
tests may provide either qualitative or
quantitative information that is
Page 7 - 4
sufficient to verify the nominal alloy
composition.
3.14 pressure-containing components:
Items that form the pressurecontaining envelope of the piping
system.
3.15 random: Selection process by
which choices are made in an arbitrary
and unbiased manner.
4
3.16 representative sample: One or
more items selected at random from
the inspection lot that are to be
examined to determine acceptability of
the inspection lot.
3.17 standard reference materials:
Sample materials for which laboratory
chemical analysis data are available
and are used in demonstrating test
instrument accuracy and reliability.
EXTENT OF VERIFICATION
Summary
This section discusses actual verification of materials including the
responsibilities, materials to be verified and control of material storage.
5
MATERIAL VARRIFICATION PROGRAM TEST METHODS
Summary
This section contains recommendations about the objectives of a PMI
program, various test methods, equipment calibration and personnel
qualifications.
6
EVALUATION OF PMI TEST RESULTS
Summary
Section 6 is a discussion of the PMI results, as stated by the owner/user, as
well as, a nonconformity program.
7
MARKING AND RECORD-KEEPING
Page 7 - 5
API RP 578
Quiz
1. API RP 578 covers PMI testing of ____________.
A.
B.
C.
D.
new construction and in-service materials
new tank construction
in-service piping
in-service vessels
2. Lot size refers to __________.
A.
B.
C.
D.
the number of items available in the inspection lot
all materials on the job site
the area inside the battery limits
the material storage area
3. A mill test report __________.
A.
B.
C.
D.
is as good as a PMI test
always supersedes a PMI test
is better than a PMI test
should not be considered a substitute for a PMI test
4. PMI testing of a weld “button” _____________.
A.
B.
C.
D.
is the only way to test welding electrodes or wires
is a test for the quality of a spot weld
will insure the base material is compatible with the stored product
may be substituted for PMI testing of an electrode
5. Persons performing PMI must be qualified by ______________.
A. training and experience
B. ASNT
C. AWS
D. ASTM
Page 7 - 6
API 578 Quiz
Answer Key
1.
2.
3.
4.
5.
A
A
D
D
A
Paragraph 1.1.
Paragraph 3.6
Paragraph 4.2.4
Paragraph 4.2.6
Paragraph 5.5
Page 7 - 7
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Page 7 - 8
Welding Terminology
WELD JOINT GEOMETRY AND WELDING TERMINOLOGY
Introduction
The American Welding Society has long realized the need for standardized terms
and definitions for use by those actively involved in the fabrication of welded
products. In answer to this need, AWS has published the document AWS A3.0,
Standard Welding Terms and Definitions. It was developed by the AWS Committee
on Definitions and Symbols to aid in the communication of welding information.
The standard terms and definitions published in A3.0 are those that should be used
in the oral and written language of welding. While these are the standard, or
preferred, terms, they are by no means the only terms used to describe various
situations. Since the purpose here is to educate, it is felt to be important to mention
some of these common terms, even though they are not preferred terminology.
When these terms are mentioned, they will appear in parentheses after the
preferred words.
While most of the terms used apply to the actual welding operation, it is important
for the welding inspector to understand other definitions which apply to other
related operations. For example, the welding inspector should understand how to
describe the various weld joint configurations and those elements of the fitup
process requiring comment. After welding is completed, the welding inspector may
need to describe the location of some welding discontinuity which has been
discovered. If such a discontinuity requires further attention, it is important that the
inspector accurately describe the location of the problem so that the welder will
know where the repair is to be made.
Page 8- 1
Types of Joints
Before welding begins, the welding inspector may be required to evaluate the weld
joint configuration and fitup. This is one of the most important aspects of welding
inspection, because it is possible to detect problems which require correction. When
discovered at this stage, these problems can be corrected more economically.
So, when a welding inspector is performing this preliminary inspection, it is
necessary that he know the differences between the various types of weld joints. A
joint is "the junction of members or edges of members which are to be joined or
have been joined." There are five basic types of joints, including: butt, corner, T-,
lap, and edge.
These five joint types get their names from their basic configuration. The butt joint
results when the two members to be joined lie in the same plane and they are
connected at their edges. With a corner joint, the two members to be joined lie in
perpendicular planes and again, their edges are connected. The T-joint is similar in
that the two members lie in perpendicular planes, except, now the edge of one
member is joined to the planar surface of the other. In a lap joint configuration, the
two members lie in parallel planes, but not the same plane. The joint occurs where
the two members overlap each other to form a double thickness region, this area is
also referred to as the faying surface. The final joint configuration, the edge, also
has the two members lying in parallel planes. With this configuration, the two
members lie with their planar surfaces in contact so that the actual welding occurs
around the perimeter, or outside, of the joint.
Parts of the Weld Joint
Once the type of joint has been identified, it may be necessary to further describe
the exact configuration required. To do this, the welding inspector must be capable
of naming the various features of that particular joint. Some of these elements
include: joint root, groove face, root face, root edge, root opening, bevel, bevel
angle, groove angle, and groove radius. Depending upon the particular type of
joint configuration, these features may take on slightly different shapes.
A perfect example of this is the joint root, or "that portion of a joint to be welded
where the members approach closest to each other. In cross section, the joint root
may be either a point, line, or an area."
By definition, groove face is "that surface of a member included in the groove." The
root face (also commonly called the land, nose or flat) is "that portion of the groove
face adjacent to the joint root." The root edge is defined as "a root face of zero
width."
These elements are often essential variables for welding procedures as well as
production welding, so the welding inspector may be required to actually measure
them to judge their compliance with applicable drawings or other documents.
Page 8- 2
The root opening is described as "the separation between the workpieces at the joint
root." The bevel (also commonly referred to as the chamfer) is "an angular edge
preparation." The bevel angle is defined as "the angle formed between the prepared
edge of a member and a plane perpendicular to the surface of the member." The
groove angle is "the total included angle of the groove between workpieces." For a
single-bevel-groove-weld, the bevel angle and the groove angle are equal. The final
term, groove radius, applies only to J- and U-groove-welds. It is described as "the
radius used to form the shape of a J- or U-groove weld." Normally, a J- or U-groove
weld configuration is specified by both a bevel (or groove) angle and a groove
radius.
Types of Welds
There are numerous welds which can be applied to the various types of joints.
According to AWS A3.0, there are 18 basic types of welds utilized for arc welding,
including:
1) Square-groove weld
2) Bevel-groove weld
3) V-groove weld
4) J-groove weld
5) U-groove weld
6) Flare-bevel-groove weld
7) Flare-V-groove weld
8) Fillet weld
9) Edge weld
10) Edge-flange weld
11) Corner-flange weld
12) Spot weld
13) Seam weld
14) Plug weld
15) Slot weld
16) Surfacing weld
17) Back weld
18) Backing weld
With this variety of groove weld geometries available, the welding fabricator can
choose the one which best suits his needs. This choice could be based on
considerations such as: accessibility, type of welding process being used, method of
joint preparation, and adaptation to particular designs of the structure being
fabricated.
The first seven categories above refer to different groove configurations. Their
names imply what the actual configurations look like when viewed in their cross
section. All of these groove weld types can be applied to joints which are welded
from a single side or both sides. As would be expected, a single-welded joint is "a
fusion welded joint that is welded from one side only." A double-welded joint is "a
fusion welded joint that is welded from both sides."
Page 8- 3
The next category of weld is the fillet weld. This type is possibly the most used of
any of the different welds. An important thing to remember is that a fillet weld is
not a type of joint. It is a particular type of weld which can be applied to a lap, T- or
corner joint. AWS A3.0 defines a fillet weld as "a weld of approximately triangular
cross section joining two surfaces approximately at right angles to each other in a
lap joint, T-joint, or corner joint."
An edge weld is described as "a weld in an edge joint." Two modifications of the
edge weld are utilized for flange welds. A flange weld is "a weld made on the edges
of two or more members to be joined, usually light gage metal, at least one of the
members being flanged." The two common types are the edge- flange weld and the
corner-flange weld. The edge-flange weld has both of the members flanged, while
the corner-flange weld is used to join two members where only one of the members
is flanged.
The next weld type of interest is the surfacing weld. As might be expected, this
particular type of weld is applied to the surface of a metal. Normally, the primary
reason for this application is to provide some barrier against abrasion or corrosion.
Often, this approach is more economical than the use of a full thickness of some
more expensive material. AWS A3.0 defines a surfacing weld as "a weld applied to a
surface, as opposed to making a joint, to obtain desired properties or dimensions.”
The final weld types to be discussed are called back and backing welds. From the
names, it is apparent that these welds are meant to be applied to the back side of a
weld joint. Although they are applied to the same location, they differ depending
upon when they are deposited. AWS A3.0 describes a back weld as "a weld made at
the back of a single groove weld," and a backing weld as "backing in the form of a
weld." Therefore, a back weld is applied after the front side has already been
welded, while the backing weld is deposited before welding the front side.
Parts of Completed Welds
So far, the discussion has been limited to the description of weld joints and types of
weld configurations. However, the welding inspector must also be aware of those
terms used to describe conditions or features of completed welds. When a
completed weld is being inspected, the inspector must be able to describe the
conditions which exist when he is required to report his inspection findings.
Therefore, it is appropriate to define the various parts of completed groove and fillet
welds, since they constitute the bulk of the weld configurations commonly
encountered.
The groove weld, regardless of its particular configuration, has several primary
components. The first part, the weld face, is "the exposed surface of a weld on the
side from which welding was done." The junction between the weld face and the
base metal surface is referred to as the weld toe. Opposite the weld face is the weld
root. The weld root is defined as "the points, as shown in cross section, at which the
back of the weld intersects the base metal surfaces." The root surface is the surface of
the weld on the side opposite from where the welding was done. Therefore, the
root surface is bounded by the weld root on either side.
The face reinforcement (also commonly called weld crown) is "the weld
reinforcement at the side of the joint from which welding was done." Conversely,
Page 8- 4
the root reinforcement is "the weld reinforcement opposite the side from which
welding was done." In both cases, this represents that portion of the weld metal
which is above the surface of the base metal.
These explanations have assumed that this was a single- welded joint, or all welding
was performed from one side. In the case where a double-sided-groove is used,
both sides of the joint will have a weld face, and the amount of buildup present on
both sides will be referred to as the face reinforcement.
Just as groove welds have names for their various parts, there is also standard
terminology for the parts of a fillet weld.
As with the groove weld, the surface of the weld which the inspector will evaluate is
referred to as the weld face. The junctions of that weld face with the base metal are
called the weld toes. The furthest penetration of the weld metal into the joint is
considered to be the weld root.
The distance from the weld toe to the joint root is called the leg. One other feature
relevant to a fillet weld which is not noted here is the weld throat. In general, this is
the shortest distance through the cross section of the weld. The various types of
weld throats will be discussed in more detail when sizing convex and concave fillet
welds is examined.
Fusion and Penetration Terminology
There are also terms relating to the fusion and penetration of the weld metal into
the base metal. Although these are features which are difficult for the visual
inspector to check without further destructive or nondestructive examination, it is
still important to understand what the various terms actually mean.
In general, fusion refers to the actual melting together of the filler metal and base
metal, or of the base metal only. Penetration is a term which relates to the distance
that the weld metal has progressed into the joint. The degree of penetration
achieved has a direct effect on the strength of the joint and is therefore related to the
weld size.
Numerous terms exist which describe the degree or location of either fusion or
penetration.
During the welding operation, the original groove face is melted such that the final
boundary of the weld metal is deeper than the original surface. The groove face is
referred to as the fusion face since it will be melted during welding. The boundary
between the weld metal and base metal is referred to as the weld interface. The
depth of fusion is the distance from the fusion face to the weld interface. The depth
of fusion is always measured perpendicular to the fusion face.
In all cases, the fusion zone, or "the area of base metal melted as determined on the
cross section of a weld" is shown as a shaded area.
Page 8- 5
There are also several terms which refer to penetration of the weld. Such
descriptions are important because the amount of penetration present has a
profound effect on the strength of a weld joint.
Root penetration is the distance that the weld metal has melted into the joint beyond
the joint root. The joint penetration is the distance from the furthest extension of
the weld into the joint to the weld face, excluding any weld reinforcement which
may be present. For groove welds, this same length is also referred to as the weld
size (also commonly referred to as effective throat). For a groove weld with no
additional edge preparation, the root penetration and joint penetration are
considered to be equal.
Weld Size Terminology
For the case of a double-groove weld configuration where the joint penetration is
less than complete, the weld size is equal to the sum of the joint penetrations from
both sides. That is, the weld size is equal to the E1 plus E2. For a complete
penetration groove weld, the weld size will be equal to the thickness of the thinner
of the two members joined, since there is no credit given for any weld
reinforcement present.
To determine the size of a fillet weld, we must first know whether the final weld
configuration is convex or concave. Convex means that the weld face exhibits some
buildup causing it to appear slightly "humped up." This is referred to as the amount
of convexity. Convexity in a fillet weld is synonymous with weld reinforcement in a
groove weld. If a weld has a concave profile, it means that its face is "dished in."
For both configurations, the fillet weld size is determined by the leg length of the
largest isosceles (two legs of equal length) right triangle which can be completely
included within the cross section of the weld. So, for the convex fillet weld, the leg
and size are equal. However, the size of a concave fillet weld is slightly less that its
leg length.
There are really three different types of weld throats with which to be concerned:
theoretical, effective and actual.
The first is the theoretical throat. This is the minimum amount of weld which the
designer counts on when a weld size is originally specified. The theoretical throat is
described as "the distance from the beginning of the joint root perpendicular to the
hypotenuse (side of the triangle opposite the right angle) of the largest right triangle
that can be inscribed within the cross section of a fillet weld."
The effective throat takes into account any additional joint penetration which may
be present. So, the effective throat can be defined as "the minimum distance minus
any convexity between the weld root and the face of a fillet weld."
Page 8- 6
The final dimension, the actual throat, takes into account both the joint penetration
as well as any additional convexity present at the weld face. Technically, the actual
throat is "the shortest distance between the weld root and the face of a fillet weld."
For a concave fillet weld, the effective throat and actual throat are equal, since there
is no convexity present.
In all of the above cases, it has been assumed that the fillet welds have equal leg
lengths. For an unequal leg fillet welds, the fillet weld size is determined by "the leg
lengths of the largest right triangle that can be inscribed within the fillet weld cross
section."
The welding inspector may also be asked to somehow determine the sizes of other
types of welds. One example might be a spot or seam weld, where the weld size is
equal to the actual nugget size or diameter. This is simply the length of weld metal
joining the two members.
For an edge or flange weld, the weld size is equal to the total thickness of the weld
from the weld root to the weld face.
Weld Application Terminology
To complete this discussion of welding terms and definitions, it seems appropriate to
mention some of the terminology associated with the actual application of welds.
Some welding procedures will refer to these details, so the welding inspector should
be familiar with their meanings. The first aspect to be covered is the difference
among the terms weld pass, weld bead and weld layer. A weld pass is a single
progression of welding along a joint. The weld bead is that weld which results from
a weld pass. A weld layer is a single level of weld within a multiple-pass weld. A
weld layer may consist of a single bead or multiple beads.
When a weld bead is deposited, it could have a different name, depending upon the
technique which the welder uses. If the welder progresses along the joint with little
or no lateral (sideways) motion, the resulting weld bead is referred to as a stringer
bead. A weave bead results when the welder manipulates the electrode laterally as
the weld is deposited along the joint. The weave bead is typically wider than the
stringer bead. Due to the amount of lateral motion used, the travel speed, as
measured along the longitudinal axis of the weld, is less than would be the case for a
stringer bead.
There are several terms which describe the actual sequence in which the welding is
to be done. This is commonly done to reduce the amount of distortion caused by
welding. Three common techniques are: backstep sequence, block sequence and
cascade sequence.
The backstep sequence is a technique where each individual weld pass is deposited
in the direction opposite that of the overall progression of welding.
Page 8- 7
A block sequence is defined as "a combined longitudinal and cross sectional
sequence for a continuous multiple pass weld in which separated increments are
completely or partially welded before intervening increments are welded." With the
block sequence, it is important that each subsequent layer is slightly shorter than the
previous one so that the end of the block has a gentle slope. This will provide the
best chance of obtaining adequate fusion when the adjacent block is filled in later.
A cascade sequence is described as "a combined longitudinal and cross sectional
sequence in which weld passes are made in overlapping layers." This method differs
from the block sequence in that now each subsequent pass is longer than the
previous one.
Summary
While numerous terms have been discussed here, that does not imply that these are
the only ones which are applied to welding. This does provide some basis upon
which the inspector can begin to understand how to describe a weld or some feature
of that weld. As the welding inspector gains experience, he will learn to correlate
these "textbook" terms with actual physical characteristics. It is only after working
with and using these terms that the welding inspector will gain full understanding of
how to describe various welding attributes.
Page 8- 8
WELD JOINT GEOMETRY AND WELDING
TERMINOLOGY
Quiz
1.
The "dictionary" for welding terms is the AWS document ____________.
a.
b
c.
d.
2.
A weld "joint" is defined as ____________.
a.
b.
c.
d.
3.
any fillet weld
any place a weld can be performed
the junction of members or edges of members which are to be
joined or have been joined
the area which is to be welded
A weld "groove face" is defined as _______________.
a.
b.
c.
d.
4.
A 2.4
D 1.1
B 1.11
A 3.0
that surface of a member included in the groove
the bevels and landing of a weld joint
the bevels and adjacent base metal
Both b and c
Which of the following is not a type of weld joint?
a.
b.
c.
d.
butt joint
corner joint
lap joint
fillet weld
Page 8- 9
5.
The surface of the weld on the side opposite from where the welding was
done is called the ______________.
a.
b.
c.
d.
6.
The exposed surface of a weld on the side from which welding was done is
called the ______________.
a.
b.
c.
d.
7.
Fusion
Dilution zone
Penetration
Weld
A weld ________ is a single progression of welding along a joint.
a.
b.
c.
d.
10.
Fusion
Dilution zone
Penetration
Weld
________ is a term which relates to the distance that the weld metal has
progressed into the joint.
a.
b.
c.
d
9.
weld face
face reinforcement
root surface
root opening
_________ refers to the actual melting together of the filler metal and
base metal, or the base metal only.
a.
b.
c.
d
8.
weld face
face reinforcement
root surface
root opening
layer
section
area
pass
A common practice to reduce distortion caused by welding is ____________.
a.
b.
c.
d
backstep sequence
weld only on one side
preheat one side and weld from the other
all of the above
Page 8- 10
WELD JOINT GEOMETRY AND WELDING
TERMINOLOGY
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
d
c
a
d
c
a
a
c
d
a
Page 8- 11
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Page 8- 12
Welding Discontinuities
WELD AND BASE METAL DISCONTINUITIES
Introduction
One of the most important parts of the welding inspector's job is the actual
evaluation of welds to determine their suitability for an intended service. During
the various stages of this evaluation, he will be looking for any irregularities in the
weld or weldment. These inconsistencies are commonly referred to as
discontinuities.
In general, a discontinuity is described as any interruption in the uniform nature of
some item. Therefore, a bump in a highway could be considered to be a type of
discontinuity, because it interrupts the smooth, uniform surface of the pavement. In
welding, some of the types of discontinuities to be concerned with are such things
as: cracks, porosity, undercut, incomplete fusion, etc.
Knowledge of these discontinuities is important to the welding inspector for a
number of reasons. First, he will be asked to visually inspect welds to determine the
presence of any of these discontinuities. If discovered, the welding inspector must
then be capable of describing their nature, location and extent. This information will
be required to successfully determine whether or not that discontinuity requires
repair, as described in the applicable job specifications.
If additional treatment is deemed necessary, the welding inspector must be capable
of accurately describing the discontinuity to the extent that it can be satisfactorily
corrected by production personnel.
Before describing these discontinuities, it is extremely important to understand the
difference between a discontinuity and a defect. Too often, people mistakenly use
the two terms interchangeably. As a welding inspector, you should strive to realize
the distinction between the terms discontinuity and defect.
While a discontinuity is some feature which introduces an irregularity in an
otherwise uniform structure, a defect is a specific discontinuity which impairs the
suitability of that structure for its intended purpose. That is, a defect is a
discontinuity of a certain type or which occurs in an amount great enough to render
that particular object or structure unsuitable for its intended service.
Page 9 - 1
In order to determine if a particular discontinuity is actually a defect, there must be
some standard which defines the acceptable limits of that discontinuity. When its
size or concentration exceeds these limits, it is deemed a defect. Therefore, think of
a defect as simply a rejectable discontinuity. So, if some feature is referred to as a
defect, it implies that it is rejectable and requires some further treatment to bring it
into acceptable limits.
Depending on the intended service of the part in question, an existing discontinuity
may or may not be considered to be a defect. Consequently, each industry utilizes a
specific code or standard which describes the acceptable limits for those
discontinuities which could affect the successful performance of various parts.
Therefore, the following discussion of weld discontinuities will deal with their
characteristics, causes and cures, without specific reference to their acceptability.
Only after their evaluation in accordance with an applicable standard can a judgment
be made as to whether they are acceptable discontinuities or rejectable defects.
However, a general discussion about the effect or criticality of certain discontinuities
can be addressed. Such a discussion will help in understanding why certain
discontinuities are forbidden, regardless of their size or extent, while the presence of
minor amounts of others is considered to be acceptable.
One way in which this can be explained relates to the specific configuration of that
discontinuity. Configurations of discontinuities can be separated into two general
groups: linear and non-linear. Linear discontinuities exhibit lengths which are much
greater than their widths. Non-linear discontinuities, on the other hand, have length
and width dimensions which are essentially the same. When present in a direction
perpendicular to the applied stress, a linear discontinuity represents a more critical
situation than does a nonlinear type, because it is more likely to propagate and
cause a failure.
Another way in which the shape of a discontinuity relates to its criticality, or effect
on the integrity of a structure, is its end condition. The end condition simply refers
to its specific sharpness. In general, the sharper the end of the discontinuity, the
more critical it becomes. This is because a sharper discontinuity is more likely to
propagate, or grow. Again, this is also dependent on its orientation with respect to
the applied stress. Linear discontinuities are most often associated with sharp end
condition. So, if there is a linear discontinuity having a sharp end condition lying
transverse to the applied stress, this represents the most dangerous situation with
respect to the ability of a member to carry some load.
If some of the more common discontinuities were to be rated with respect to the
sharpness of their end conditions, starting with the sharpest, they would tend to be:
cracks, incomplete fusion, slag inclusions, and porosity. This order coincides with
the amounts of these discontinuities permitted by most codes. There are only a few
instances in which any amount of cracking is allowed. Incomplete fusion may also
be forbidden or at least limited to minor amounts. Most codes will permit the
presence of small amounts of slag and virtually all will allow some porosity.
Depending on the industry and the intended service, these amounts will vary, but in
general the sharper the discontinuity, the more its presence is restricted.
Page 9 - 2
To further explain the importance of the end condition on the severity of a
discontinuity, consider the example of how a crack's propagation could be stopped
using a technique which you may have seen performed on some noncritical part.
The technique referred to here is the placement of a drilled hole at the end of a crack
in some material. While this does not correct the cracking, it may stop its further
propagation. This is accomplished because the sharp ends of the crack are rounded
sufficiently to reduce the stress concentration to the point that the material can
withstand the applied load.
A final way in which the criticality of a discontinuity is judged relates to the way in
which a part or structure will be loaded during service. For example, if a weld forms
a part of some pressure boundary, those discontinuities constituting a significantly
long leak path will be most damaging. In the case of a structure which will be
loaded in fatigue (i.e. cyclic loading) those discontinuities forming sharp notches on
the surface of the structure will cause failure more readily than those beneath the
surface. That is because they form a stress riser which tends to concentrate, or
amplify, the stresses at that point. Such a stress concentration will result in a
localized overload condition even though the stress applied to the full cross section
may be low.
This can be shown by the example of a piece of welding wire which you would like
to break. One way of accomplishing this would be to bend the wire back and forth
until it finally broke. However, it may take many cycles to produce this failure. If
you were to take a similar piece of welding wire, place it on a hard surface, and
strike it with the sharp edge of a chipping hammer, you would produce a sharp
notch on the wire's surface. Now, only one or two bends would be necessary to
result in the failure of that wire, because the notch represents a significant stress
concentration.
So, for a structure which must withstand fatigue loading, the surfaces should be free
of those discontinuities which provide sharp notches. Consequently, parts subjected
to fatigue loading in service are often required to have their surfaces machined to
very smooth finishes. Abrupt changes in contour are also avoided.
For these types of components, one of the most effective methods of inspection is
visual. Therefore, you, as a welding inspector, can play an extremely important role
in determining how well these components will behave in service. So, in general,
you can judge the suitability of these structures for their intended service simply
based on the presence and/or sharpness of any surface discontinuities.
Page 9 - 3
Weld and Base Metal Discontinuities
Having provided this background, let's now discuss some of the more common
weld and base metal discontinuities. Those with which will be discussed are listed
below.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
cracks
incomplete fusion
incomplete penetration
slag inclusions
porosity
undercut
underfill
coldlap
convexity
weld reinforcement
arc strikes
tungsten inclusions
spatter
laminations
lamellar tears
dimensional
Cracks
The first of these discontinuities to be discussed is the crack. This is appropriate,
since the crack is generally considered to be the most critical discontinuity which is
covered in this chapter. This criticality is due to the fact that cracks are characterized
as being linear as well as exhibiting very sharp end conditions. Since the ends of
cracks are extremely sharp, there is a tendency for the crack to grow, or propagate,
further if some additional stress is applied.
Cracks are initiated when the load, or stress, applied to a member exceeds its tensile
strength. In other words, there is an overload condition. While the applied load
may not exceed the load carrying ability of some member, the presence of some
notch, or stress riser, could cause the localized stress at the tip of the stress riser to
exceed the tensile strength of the material. In such a case, cracking could occur at
this stress concentration. Therefore, cracking is commonly associated with both
surface and subsurface discontinuities which provide such a stress riser.
Cracks can be categorized in several different ways. One way of grouping cracks is
by characterizing them as either hot or cold cracks. This is an indication of when the
cracking occurred, or at least the temperature at which the fracture occurred. This is
often a way in which it can decided exactly why a particular crack resulted, since
some types of cracks are characteristically either hot or cold cracks.
Page 9 - 4
Hot cracks occur as the metal solidifies, at some elevated temperature. The
propagation of these cracks is considered to be intergranular; that is, the cracks
occur between individual grains. If the fracture surfaces of a hot crack are observed,
various temper colors indicating the presence of that crack at an elevated
temperature may be seen. Cold cracks occur after the metal has cooled to ambient
temperature. Those cracks resulting from service conditions would be considered
cold cracks. Delayed, or underbead, cracks resulting from entrapped hydrogen
would also be categorized as cold cracks. The propagation of cold cracks can be
either intergranular or transgranular; that is, either between or through the
individual grains, respectively.
Cracks can also be described by their direction with respect to the longitudinal axis
of the weld. Those lying in a direction parallel to the longitudinal axis are referred to
as longitudinal cracks. Similarly, those cracks lying perpendicular to the weld's
longitudinal axis are called transverse cracks. These directional references apply to
cracks occurring in either the weld or base metals. Longitudinal cracks can result
from transverse shrinkage stresses of welding or stresses associated with service
conditions.
Transverse cracks are generally caused by the longitudinal shrinkage stresses of
welding acting on weld or base metals of low ductility.
Finally, various types of cracks can further be differentiated between by giving a
description of their exact locations with respect to the various parts of the weld.
These descriptions include: throat, root, toe, crater, underbead, heat affected zone,
and base metal cracks.
Throat cracks are so named because they extend through the weld along the weld
throat, or the shortest path through the weld's cross section. They are longitudinal
cracks and are generally considered to be hot cracks. A throat crack can be
observed visually on the weld face, consequently the term centerline crack is often
used to describe this condition.
Joints exhibiting high restraint transverse to the weld axis are susceptible to this type
of cracking, especially in situations where the weld cross section is small. So, such
things as thin root passes and concave fillet welds could result in a throat cracks,
because their reduced cross sections may not be sufficient to withstand the
transverse weld shrinkage stresses.
Root cracks are also longitudinal; however, their propagation may be in either the
weld or base metal. They are referred to as root cracks because they initiate at the
weld root or the root surface of the weld. Like throat cracks, they are generally
related to the existence of shrinkage stresses from welding. Therefore, they are
usually considered to be hot cracks. Root cracks often result when joints are
improperly fitted or prepared. Large root openings, for example, may result in a
stress concentration to produce root cracks.
Page 9 - 5
Toe cracks are base metal cracks which propagate from the toes of welds. Weld
configurations exhibiting weld reinforcement or convexity may provide a stress
riser at the welds' toes. This, combined with a less ductile microstructure in the heat
affected zone increase the susceptibility of the weldment to toe cracks. Toe cracks
are generally considered to be cold cracks. The stress causing the occurrence of toe
cracks could be the result of either the transverse shrinkage stresses of welding,
some applied service stresses, or a combination of the two. Toe cracks occurring in
service are often the result of fatigue loading of welded components.
Crater cracks occur at the termination point of individual weld passes. If the
technique utilized by the welder to terminate the arc does not provide for complete
filling of the molten weld puddle, the result could be a shallow region, or crater, at
that location. The presence of this thinned area, combined with the shrinkage
stresses from welding, may cause individual crater cracks or networks of cracks
radiating from the center of the crater. When there is a radial array of crater cracks,
they are commonly referred to as star cracks.
Since crater cracks occur during the solidification of the molten puddle, they are
considered to be forms of hot cracks.
Crater cracks can be extremely dangerous because there is a tendency for the crack
to propagate further.
Although the primary cause of crater cracks relates to the technique utilized by the
welder to terminate a weld pass, these cracks can also result from the use of filler
metals having flow characteristics which produce concave profiles when solidified.
An example of this phenomena is the use of those stainless steel covered electrodes
bearing designations ending with "-16" (i.e. E308-16, E309-16, E316-16, etc.). This
ending designates a titania type coating which will produce a characteristically flat or
slightly concave weld profile. Consequently, when these electrodes are utilized, the
welder must take extra precautions and fill the craters sufficiently to prevent crater
cracks.
The next category of crack is the underbead crack. Although related to the welding
operation, the underbead crack is located in the heat affected zone instead of the
weld metal. As the name implies, it will characteristically lie directly adjacent to the
weld fusion line in the heat affected zone. When cross sectioned, underbead cracks
will often appear to run directly parallel to the fusion line of a weld bead. Although
most commonly found within the metal, they may propagate to the surface to allow
for their discovery during visual inspection.
Underbead cracking is a particularly dangerous type of crack because it may not
propagate until many hours after welding has been completed. For this reason,
underbead cracks are sometimes referred to as delayed cracks. Consequently, for
those materials which are more susceptible to this type of cracking, final inspection
should not be performed until 48 to 72 hours after the weld has cooled to ambient
temperature. High strength steels are particularly susceptible to this type of
cracking.
Page 9 - 6
Underbead cracks result from the presence of hydrogen in the weld zone. The
hydrogen could come from the filler metal, base metal, surrounding atmosphere or
surface contamination. If there is some source of hydrogen present during the
actual welding operation, it may be absorbed by the molten weld metal. When
molten, the metal can hold a great deal of this atomic hydrogen. However, once
solidified, the metal has much less capacity for the hydrogen. The tendency of the
hydrogen is to move through the metal structure to grain boundaries in the heat
affected zone. At this point, individual atoms of hydrogen may combine to form
hydrogen molecules (H2). This gaseous form of hydrogen requires more volume
and is now too large to move through the metal structure. These molecules are
now trapped. If the surrounding metal does not exhibit sufficient ductility, this
internal pressure created by the trapped hydrogen can result in underbead cracking.
The welding inspector should be aware of this potential problem and take
precautions to prevent its occurrence. The best technique for the prevention of
underbead cracking is to simply eliminate sources of hydrogen when welding
susceptible materials. With SMAW, for example, low hydrogen electrodes may be
utilized. When specified, they should be properly stored in an appropriate holding
oven to maintain this low moisture level. If allowed to remain in the atmosphere
for prolonged periods, they may pick up enough moisture to cause cracking. Parts
to be welded should be cleaned adequately to eliminate any surface sources of
hydrogen. Preheat may also be prescribed to help eliminate this cracking problem.
Since the heat affected zone is typically less ductile than the surrounding weld and
base metal, cracking may occur there without the presence of hydrogen. In
situations of high restraint, shrinkage stresses may be sufficient to result in heat
affected zone cracking, especially in the case of brittle materials such as cast iron. A
particular type of heat affected zone crack which has already been discussed is the
toe crack.
Cracking may also be present in the base metal itself. These types of cracks may or
may not be associated with the weld. Quite often, base metal cracks are associated
with stress risers which result in cracking once the part has been placed in service.
Radiographically, cracks appear as fine, rather well-defined dark lines which can be
differentiated from other linear discontinuities because their propagation path is not
perfectly straight, but tends to wander as the crack follows its path of least resistance
through the material's cross section.
Incomplete Fusion
By definition, incomplete fusion is described as the condition where the weld is not
completely fused either to the base metal or to adjacent weld passes. That is, the
fusion is less than that specified for a particular weld. Due to its linearity and
relatively sharp end condition, incomplete fusion represents a significant weld
discontinuity. It can occur at numerous locations within the weld zone. Quite often,
incomplete fusion also has associated with it slag inclusions. In fact, the presence of
slag due to insufficient cleaning may prevent the fusion from occurring.
Page 9 - 7
It is important to note that some of the examples above depict incomplete fusion
which occurs at the weld root. These conditions are most commonly referred to as
incomplete penetration since that term better describes the nature and location of
these flaws. However, AWS has decided to refer to any discontinuity where
adequate fusion has not been attained as incomplete fusion.
Incomplete fusion is most often thought of as being some internal weld flaw.
However, it can occur at the surface of the weld as well.
Another common term for incomplete fusion is cold lap. This term is often used to
describe incomplete fusion between the weld and base metal or between individual
weld passes.
Incomplete fusion can result from a number of conditions or problems. Probably
the most common cause of this discontinuity is the improper manipulation of the
welding electrode by the welder. Some processes are more prone to this problem
because there is not enough concentrated heat to adequately melt and fuse the
metals. For example, when using short circuiting transfer GMAW, the welder must
concentrate on directing the welding arc at every location of the weld joint where
fusion is required. Otherwise, there will be areas which do not exhibit the proper
amount of melting, and therefore fusion.
In other situations, the actual configuration of the weld joint may limit the amount
of fusion which can be attained. Such things as insufficient groove angles and
excessive root faces could result in incomplete fusion. Finally, extreme
contamination, including mill scale and tenacious oxide layers, could also prevent the
attainment of complete fusion.
On a radiograph, incomplete fusion will appear as darker density lines which are
generally straighter than the images of either cracks or elongated slag. The lateral
position of these indications on the film will be a hint as to their actual depth.
Incomplete Penetration
According to AWS A3.0, incomplete penetration is a nonstandard term. However,
as indicated in the discussion of incomplete fusion, incomplete fusion which occurs at
the weld root is often referred to as incomplete penetration. So, although
incomplete penetration is not the standard terminology, it actually better describes
the nature and location of this type of discontinuity.
Another way to think of the difference is that incomplete penetration will be related
to the root face of the joint. It describes the situation where the weld metal has not
completely progressed into the weld root to fuse with the existing root face. Since
penetration terminology relates to the weld size, an incompletely penetrated joint
will not have the required effective throat, or cross section to transmit the applied
loads from one member to the other.
Therefore, it is important for the welding inspector to understand what is meant by
the term incomplete penetration since it will often be used to describe incomplete
fusion at the weld root.
Page 9 - 8
There is another AWS term, partial joint penetration, which describes the situation
where a portion of the weld joint is intentionally left unfused, or penetrated. So,
incomplete penetration, or incomplete fusion, should only be applied in cases where
the intent was to provide a weld joint having complete penetration or fusion.
Incomplete penetration can be caused by the same conditions which result in
incomplete fusion; that is, improper technique, improper joint configuration, or
excessive contamination.
The radiographic image caused by incomplete penetrations will typically be a dark,
straight line. It will usually be much straighter than incomplete fusion because it is
associated with the original weld preparation at the root. It will normally be
centered in the width of the weld.
Slag Inclusions
Slag inclusions, as the name implies, are regions within the weld cross section or at
the weld surface where the molten flux used to protect the molten metal is
mechanically trapped within the solidified metal. This solidified flux, or slag,
represents a portion of the weld's cross section where the metal is not fused to itself.
This can result in a weakened condition which could impair the serviceability of the
component. Although slag inclusions are normally thought of as being totally
contained within the weld cross section, they are sometimes observed at the surface
of the weld as well.
Like incomplete fusion, slag inclusions can occur between the weld and base metal
or between individual weld beads. In fact, slag inclusions are often associated with
incomplete fusion.
Slag inclusions can only result when the process being used employs some type of
flux shielding. They are most often caused by improper techniques used by the
welder. Such things as improper manipulation of the welding electrode and
insufficient cleaning between passes can result in the presence of slag inclusions.
Often, the improper manipulation of the electrode or incorrect welding parameters
could result in undesirable weld profiles which could then hinder cleaning of the slag
between passes. Subsequent welding would then cover the trapped slag to produce
slag inclusions.
Since the density of slag is much less than that of metals, slag inclusions will appear
on a radiograph as relatively dark indications, having rather irregular shapes.
Page 9 - 9
Porosity
AWS A3.0 describes porosity as cavity type discontinuities formed by gas
entrapment during solidification. Therefore, porosity can be thought of as being
voids or gas pockets within the solidified weld metal. Due to its characteristically
spherical shape, porosity is normally considered to be the least dangerous
discontinuity. However, in cases where a weld must form some pressure boundary
to contain a gas or liquid, porosity might then be considered to be more dangerous.
This is due to the fact that the porosity might provide a leak path having some
significant length.
Like cracking, there are several different names given to specific types of porosity.
They refer, in general, to the relative locations of several pores or the specific shape
of the individual pores. Therefore, such names as uniformly scattered porosity,
cluster porosity, linear porosity, and piping porosity are used to better define the
occurrence of porosity. In cases where only a single gas pocket is found, it will
commonly be described as an isolated pore.
Uniformly scattered porosity refers to numerous pores which occur throughout the
weld in no particular pattern. Cluster porosity and linear porosity, however, refer
to specific patterns of several pores. Cluster porosity describes a number of pores
grouped together while the term linear porosity refers to a number of pores which
are grouped in a straight line.
With these types, the pores are usually spherical in shape. However, with piping
porosity, the pores are elongated. For this reason, they may be referred to as
elongated or wormhole porosity. Piping-type porosity represents the most
dangerous condition if liquid or gas containment is the primary function of the weld,
because these elongated pores represent a more significant length of leak path.
This condition may also be referred to as a pockmark. Such a condition results
when gases are trapped between the molten metal and solidified slag. One situation
in which this phenomenon can occur is when the depth of granular flux utilized for
SAW is excessive. When this occurs, the weight of the flux may be too great to
permit the gas to escape properly.
Porosity is normally caused by the presence of contaminants or moisture in the
weld zone which decompose due to the welding heat and form gases. This
contamination or moisture could come from the electrode, the base metal, the
shielding gas, or the surrounding atmosphere. However, variations in the welding
technique could also cause this porosity. An example would be the use of an
excessively long arc during SMAW with a low hydrogen type electrode. Another
example would be the use of excessively high travel speeds with SAW to result in
piping porosity. Therefore, when porosity is encountered, it is a signal that some
aspect of the welding operation is out of control. It is then time to investigate
further to determine what factor, or factors, are responsible for the presence of this
weld discontinuity.
When porosity is shown on a weld radiograph, it will appear as a well-defined dark
region, because it represents a significant loss of material density. It will normally
appear as a round indication except in the case of piping porosity. This type of
porosity will have a tail associated with the rounded indication.
Page 9 - 10
Undercut
Undercut is a surface discontinuity which occurs in the base metal directly adjacent
to the weld. It is a condition in which the base metal has been melted away during
the welding operation and there was insufficient filler metal deposited to adequately
fill the resulting depression. The result is a linear groove in the base metal which
may have a relatively sharp configuration. Since it is a surface condition, it is
particularly dangerous for those structures which will be loaded in a fatigue manner.
It is interesting to note that for groove welds, the undercut may occur at either the
face or root surface of the weld.
The visual appearance of undercut at a fillet weld has a definite shadow produced by
the undercut when the illumination is properly positioned. Experienced welding
inspectors understand this phenomenon and utilize techniques such as laying a
flashlight on the base metal surface to result in a shadow being cast in any location
where undercut exists.
Another technique is to perform final visual inspection of the weldment after
painting, especially when the paint being used is a light color such as white or
yellow. When viewed under normal lighting, the shadows cast by the presence of
undercut are much more pronounced. The only problem with this technique is that
the paint must be removed from the undercut area prior to any repair welding to
prevent the occurrence of other discontinuities such as porosity.
Undercut is normally the result of improper welding technique. More specifically, if
the weld travel speed is excessive, there may not be sufficient filler metal deposited
to adequately fill depressions caused by the melting of the base metal adjacent to the
weld. Undercut could also result when the welding heat is too high, causing
excessive melting of the base metal.
When noted on a radiograph, undercut will appear as a dark, fuzzy indication at the
edge of the weld reinforcement.
Underfill
Underfill, like undercut, is a surface discontinuity which results in a loss of material
cross section. However, underfill occurs in the weld metal of a groove weld
whereas undercut is found in the base metal adjacent to the weld. In simple terms,
underfill results when there is not sufficient filler metal deposited to adequately fill
the weld joint.
Like undercut, underfill can occur at both the face and root surfaces of the weld.
Underfill at the weld root of pipe welds is sometimes referred to as suckback,
because it can be caused by excessive heating of the root pass during deposition of
the second pass (or hot pass).
As with undercut, when the lighting is properly oriented, there is a shadow
produced because of the surface depression.
Page 9 - 11
The primary cause of underfill is the technique employed by the welder. Excessive
travel speeds do not allow sufficient filler metal to be melted and deposited to fill the
weld zone to the level of the base metal surface.
Coldlap
Another surface discontinuity which can result from improper welding techniques is
coldlap. Coldlap is described as the protrusion of weld metal beyond the weld toe
or weld root. It appears as though the weld metal overflowed the joint and is laying
on the adjacent base metal surface. Due to its characteristic appearance, coldlap is
sometimes referred to as rollover.
As was the case for both undercut and underfill, coldlap can occur at either the weld
face or weld root of groove welds.
Once again, there is a definite shadow cast when the lighting is properly oriented.
Coldlap is considered to be a significant discontinuity since it can result in a sharp
notch at the surface of the weldment. Further, if the amount of overlap is great
enough, it could hide a crack which may propagate from this stress riser.
The occurrence of coldlap is normally due to an improper technique utilized by the
welder. That is, if the welding travel speed is too slow, the amount of filler metal
melted will be in excess of that amount required to sufficiently fill the joint. The
result is that this excessive metal simply lays on the base metal surface without
fusing. Some types of filler metals are more prone to this type of discontinuity
since, when molten, they are too fluid to resist the forces of gravity. Therefore, they
may only be used in positions in which gravity will tend to hold the molten metal in
the joint.
Convexity
This particular weld discontinuity applies only to fillet welds. Convexity refers to
the amount of weld metal buildup on the face of the fillet weld. By definition, it is
the maximum distance from the face of a convex fillet weld perpendicular to a line
joining the weld toes.
Within certain limits, convexity is not damaging. In fact, a slight amount of
convexity is desirable from a fillet weld strength standpoint. However, when the
amount of convexity exceeds some limit, this discontinuity becomes a significant
flaw. The fact that additional weld metal is present is not the real problem, unless
one considers the economics of depositing more filler metal than is absolutely
necessary. The real problem created by the existence of excess convexity is that the
resulting fillet weld profile now has sharp notches present at the weld toes. These
notches can produce stress risers which could weaken the structure, especially when
that structure is loaded in fatigue. Therefore, excessive convexity can be corrected
by either removing excess metal from the fillet weld face or by depositing additional
weld metal at the weld toes to provide a smoother transition between the weld and
base metals.
Page 9 - 12
The solution to the problem where the convexity present on a reinforcing fillet weld
resulted in a stress riser which caused a fatigue crack to initiate during service was to
prescribe machining to provide a concave profile which eliminated the stress
concentration.
Convexity results when welding travel speeds are too slow or when the electrode
manipulation is improper. The result is that excess filler metal is deposited and it
does not properly wet the base metal surfaces. The presence of contamination on
the base metal surface or the use of shielding gases which do not adequately clean
away these contaminants can also result in this undesirable fillet weld profile.
Weld Reinforcement
Weld reinforcement is similar to convexity except that it describes a condition which
can only be present in a groove weld. Weld reinforcement is described as that weld
metal in excess of the amount required to fill a joint. Two other terms, face
reinforcement and root reinforcement, are specific terms which describe the
presence of this reinforcement on a particular side of the welded joint. As the names
imply, face reinforcement occurs on the side of the joint from which welding was
done and root reinforcement occurs on the opposite side of the joint.
For a weld joint welded from both sides, the reinforcement on both sides is
described as the face reinforcement.
Like convexity, the problem associated with this discontinuity lies with the sharp
notches that are created instead of the fact that there is more weld metal present
than is necessary. The greater the amount of weld reinforcement, the more severe
the notches.
As the reinforcement angle increases (caused by an increase in the amount of weld
reinforcement) there is a drastic decrease in the fatigue resistance of the weld joint.
Most codes prescribe maximum limits for the amount of weld reinforcement
permitted. However, simply reducing the amount of weld reinforcement does not
really improve the situation. Only after performing blend grinding to increase the
weld reinforcement angle is the situation really improved. Simple grinding to
remove the top of the weld reinforcement does nothing to decrease the sharpness
of the notches at the weld toes.
Excessive weld reinforcement results from the same reasons a given for convexity,
with the actual welding technique being the predominant cause.
Page 9 - 13
Arc Strikes
The presence of arc strikes represents a very dangerous base metal discontinuity.
Arc strikes (or arc burns) result when the arc is initiated on the base metal surface
away from the weld joint, either intentionally or accidentally. When this occurs,
there is a localized area of the base metal surface which is melted and then rapidly
cooled due to the massive heat sink created by the surrounding base metal. On
certain materials, especially high strength steels, this can produce a localized heat
affected zone which may contain martensite. If this brittle microstructure is
produced, the tendency for cracking could be great. Numerous failures of
structures and pressure vessels can be traced to the presence of a welding arc strike
which provided a crack initiation site to result in a catastrophic failure. Arc strikes
can provided a crack initiation site which results in the ultimate failure of the
specimen.
Arc strikes are normally caused by improper welding techniques. Welders should
be warned of the dangers of arc strikes. Due to the danger they pose, arc strikes
should never be permitted. The welder should not be performing production
welding if he insists on initiating the welding arc outside of the weld joint. So, it
becomes a matter of discipline. Improper connection of the ground clamp to the
work can also result in the production of arc strikes.
Another important note applies to the inspection of welds using the prod type
magnetic particle method. Since this method relies on the conduction of electricity
through the part to produce the magnetic field, the possibility exists that arc strikes
could be produced during the inspection if there is not adequate contact between the
prods and the metal surface. Although not as severe as welding arc strikes, these
arc burns could also produce harmful effects.
Tungsten Inclusions
Tungsten inclusions are almost always associated with the GTAW process, which
utilizes a tungsten electrode to produce an arc, and therefore the heat for the
welding. If the tungsten electrode makes contact with the molten puddle, the arc
could go out and the molten metal can solidify around the tip of the electrode.
Upon removal, the tip of the electrode will most likely break off and could be
included in the final weld if not removed by grinding.
Tungsten inclusions could also result when the welding current being used for
GTAW is in excess of that recommended for a particular diameter of electrode. In
such a case, the current density may be great enough that the electrode starts to
decompose and pieces may be deposited in the weld metal. This could also occur if
the welder does not properly grind the point on the tungsten electrode. If the
grinding marks are oriented such that they form rings around the electrode instead
of being aligned with its axis, they could form stress risers which might cause the tip
of the electrode to break off preferentially.
Page 9 - 14
Other reasons for the occurrence of tungsten inclusions include:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
contact of filler metal with hot tip of electrode;
contamination of the electrode tip by spatter;
extension of electrodes beyond their normal distances
from the collet, resulting in overheating of the electrode;
inadequate tightening of the collet;
inadequate shielding gas flow rates or excessive wind drafts
resulting in oxidation of the electrode tip;
use of improper shielding gas;
defects such as splits or cracks in the electrode;
use of excessive current for give size electrode;
improper grinding of the electrode; or
use of too small of an electrode.
Tungsten inclusions are seldom found on the surface of the weld unless the welding
inspector has the opportunity to look at an intermediate pass after a piece of
tungsten has been deposited. The primary way in which tungsten inclusions are
revealed is through the use of radiography. Since tungsten has a greater density
than steel or aluminum, it will show up as a definite light area on the radiographic
film.
Spatter
AWS A3.0 describes spatter as metal particles expelled during fusion welding that do
not form a part of the weld. We more commonly think of those particles which are
actually attached to the base metal adjacent to the weld. However, particles which
are thrown away from the weld and base metal are also considered to be spatter.
For that reason, another definition might be those particles of metal which comprise
the difference between the amount of metal melted and the amount of metal
actually deposited in the weld joint.
In terms of criticality, spatter may not be of great concern. However, large globules
of spatter may have sufficient heat to cause a localized heat affected zone on the
base metal surface similar to the effect of an arc strike. Also, the presence of spatter
on the base metal surface could provide a localized stress riser which could cause
problems during service. The presence of this stress concentration along with a
corrosive environment resulted in a form of stress corrosion cracking known as
caustic embrittlement.
When spatter is present, however, it does detract from the otherwise pleasing
appearance of a satisfactory weld.
Page 9 - 15
Another feature of spatter which could result in problems has to do with the
irregular surface which is produced. During inspection of the weld using various
nondestructive methods, the presence of spatter could either prevent the
performance of a valid test or produce irrelevant indications which could mask real
weld flaws. For example, the presence of spatter adjacent to a weld may prevent
adequate coupling of the transducer during ultrasonic testing. Also, spatter could
cause problems for both the performance and interpretation of magnetic particle
and penetrant testing.
Spatter can result from the use of high welding currents which can cause excessive
turbulence in the weld zone. Some welding processes are considered to
characteristically produce greater amounts of spatter than others. For example,
short circuiting and globular transfer GMAW tend to produce more spatter than the
use of spray transfer. Another feature which will control the amount of spatter
produced is the type of shielding gas used for GMAW and FCAW. The use of argon
mixtures will reduce the amount of spatter compared to the amount produced when
straight CO2 shielding gas is utilized.
Lamination
This particular discontinuity is a base metal flaw. Laminations result from the
presence of nonmetallic inclusions which occur in steel when it is being produced.
These inclusions are normally forms of oxides which are produced when the steel is
still molten. During subsequent rolling operations, these inclusions become
elongated to form stringers. If these stringers are particularly large, they are
referred to as laminations. The most massive form of lamination arises from pipe
which develops in the upper part of the steel ingot during the final stages of
solidification, and which, on infrequent occasions, is not completely cropped off the
ingot during rolling to plate or bar. The pipe cavity usually contains some complex
oxides, which are rolled out within the laminations.
The heat of fusion joining is sufficient to remelt the stringers in the zone
immediately adjacent to the weld, and the ends of the stringers may either fuse or
they may open up.
Laminations may also show up during thermal cutting, where the heat of the cutting
operation may be sufficient to open the stringers to the point that they can be
visually observed. Another term related to laminations is a delamination. This
simply refers to a particular lamination which exhibits some visual separation
between layers instead of being a very tight void.
Laminations may or may not present a dangerous situation, depending on the way
in which the structure is loaded. If the stresses are acting on the material in a
direction perpendicular to the lamination, it will severely weaken the structure.
However, laminations oriented parallel to the applied stress, may not cause great
concern.
If a lamination is present on the surface of a weld preparation, it could cause further
problems during welding. In such a case, weld metal cracks could propagate from
those laminations due to the stress concentration which results.
Page 9 - 16
Another problem related to the presence of laminations open to the groove face is
that they are prime sites for the accumulation of hydrogen. So, during welding this
hydrogen could be included in the molten metal and provide a necessary element
for the occurrence of underbead cracking.
Since laminations are the result of the steel making process itself, there is little that
can be done to prevent their occurrence. Purchasing steels having low levels of
contaminants will drastically reduce the tendency toward the presence of
laminations. However, the welder and welding inspector can do little to prevent
their occurrence. About all that can be done is to perform an adequate visual
and/or nondestructive examination to reveal the presence of laminations before a
piece of laminated material is included in a weldment.
The best method for the discovery of laminations other than visual inspection is the
use of ultrasonic testing. Radiography will not reveal laminations because there is
no change in the radiographic density of a metal even if it is laminated. To illustrate
this, imagine the radiography of two 1/4 inch plates place one on top of the other
compared to a single 1/2 inch plate. Review of the film would reveal no difference
in density, because the radiation is still passing through the same total thickness of
metal.
Lamellar Tear
Another base metal discontinuity of importance is the lamellar tear. It is described
as a terrace-like fracture in the base metal with a basic orientation parallel to the
rolled surface. Lamellar tears occur when there are high stresses in the throughthickness direction resulting from welding shrinkage. The tearing always lies within
the base metal, usually outside the heat affected zone and generally parallel to the
weld fusion boundary.
Lamellar tearing is a discontinuity most directly related to the actual configuration of
the joint. Therefore, those joint configurations in which the shrinkage stresses from
welding are applied in a direction which tends to pull the rolled material in its
through-thickness or z-axis direction will be more susceptible to lamellar tearing.
When a metal is rolled, it will characteristically exhibit lower strength and ductility in
this direction as compared to its properties in the longitudinal and transverse
directions.
Other factors affecting a material's susceptibility to lamellar tearing are its thickness
and the degree of contaminants present. The thicker the material and the higher the
inclusion content, the greater the possibility of experiencing lamellar tearing.
For the onset of lamellar tearing, three conditions must exist simultaneously. They
are: stress in the through-thickness direction, susceptible joint configuration, and
material having a high inclusion content. So, to prevent the occurrence of lamellar
tearing, any one of these elements must be eliminated.
Page 9 - 17
Since this discontinuity is so closely related to the actual configuration of the weld
joint, the experienced welding inspector should be able to spot those situations in
which lamellar tearing may occur. Once that is recognized, there is a good
possibility that the problem can be avoided.
Dimensional
Up to this point, all of the discontinuities discussed could be classified as structural
type flaws. However, there is another group of discontinuities which can be
classified as dimensional irregularities. Dimensional discontinuities are simply size
and/or shape imperfections. These irregularities can occur in the welds themselves
or in the overall welded structure. Since dimensional discontinuities could render a
structure unsuitable for its intended service, they must be considered and checked
by the welding inspector.
This inspection could consist of the measurement of weld sizes and lengths to assure
that there is sufficient weld metal to transmit the applied loads. Other
measurements should be made of the entire weldment to assure that the heat of
welding has not caused excessive distortion or warpage.
Summary
Imperfections may exist in the weld and/or base metal. They are generally
described as discontinuities. If a certain discontinuity is of sufficient size, it may
render a structure unfit for its intended service. Codes normally dictate the
permissible limits for discontinuities. Those greater than these limits are termed
defects. Defects are discontinuities which require some corrective action.
Discontinuity severity is based on a number of factors, including: whether it is linear
or nonlinear, the sharpness of its ends, and whether it is open to the surface or not.
Discontinuities exist in a number of different forms, including: cracks, incomplete
fusion, incomplete penetration, slag inclusions, porosity, undercut, underfill, coldlap,
convexity, weld reinforcement, arc strikes, tungsten inclusions, spatter, laminations,
lamellar tears, seams/laps, and dimensional.
By knowing how these discontinuities can form, the welding inspector may be
successful at spotting these causes and prevent the problem from occurring.
Page 9 - 18
Weld and Base Metal Discontinues
Quiz
1.
One of the most important parts of the welding inspector's job is the actual
evaluation of welds to determine _______.
a.
b.
c.
d.
e.
2.
A ________ is some feature which introduces an irregularity in an
otherwise uniform structure.
a.
b.
c.
d.
3.
defect
fault
discontinuity
none of the above
A ______ is a feature which impairs the suitability of that structure for its
intended purpose.
a.
b.
c.
d.
4.
their suitability for an intended service
appearance
rating
all of the above
none of the above
defect
fault
discontinuity
none of the above
Generally, ________ are considered to be the most critical discontinuity.
a.
b.
c.
d.
undercut
cracks
overlap
porosity
Page 9 - 19
5.
__________ is described as the condition where the weld is not
completely fused either to the base metal or to adjacent weld passes.
a.
b.
c.
d.
6.
________ describes the situation where the weld metal has not
completely progressed into the weld root to fuse with the existing
root face.
a.
b.
c.
d.
7.
Crack
Lamination
Porosity
Undercut
A discontinuity that appears as though the weld metal overflowed the
joint and is laying on the adjacent base metal surface is called ________.
a.
b.
c.
d.
10.
Incomplete penetration
Incomplete fusion
Overlap
none of the above
________ is defined as a cavity type discontinuity formed by gas
entrapment during solidification.
a.
b.
c.
d.
9.
Incomplete penetration
Incomplete fusion
Porosity
none of the above
_________ are regions within the weld cross section or at the weld
surface where the molten flux is mechanically trapped within the
solidified metal.
a.
b.
c.
d.
8.
Incomplete penetration
Incomplete fusion
Porosity
none of the above
incomplete penetration
incomplete fusion
overlap
none of the above
Which of the following is true about laminations?
a.
b.
c.
d.
e.
a base metal flaw
result from the presence of nonmetallic inclusions which occur in
steel
were formed when the steel was produced
all of the above
none of the above
Page 9 - 20
Weld and Base Metal Discontinues
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
a
c
a
b
b
a
d
c
c
d
Page 9 - 21
(This page intentionally left blank)
Page 9 - 22
ASME Section IX
API 570
ASME Section IX
ASME Section IX was developed to provide a common location for welding
qualifications for the ASME Codes. The intent of Section IX is to provide
information on the qualifications of welding procedures and welding personnel for
the new construction of boilers and pressure vessels. Section IX is now referenced
by other codes such as API 570 and most other API Standards.
The organization of Section IX is described in the introduction.
Article I is the general article and contains information relative to the remainder of
the book. The paragraphs in Article I are numbered QW-100. Article I contains the
acceptance criteria, types of tests, etc.
Article II deals with welding procedure qualifications. The paragraphs in Article II
are numbered QW-200.
Article III provides the information needed to qualify welders and operators. The
paragraphs in Article III are numbered QW-300.
Article IV is titled Welding Data, this article contains the variables, tables and figures
used to qualify personnel and procedures. NOTE: Do not go to Article IV unless
one of the other articles references you there.
Article V, Standard Welding Procedure Specifications (SWPS). This section gives the
details for allowing the use of prequalified procedures , as outlined by the American
Welding Society.
The forward of Section IX contains the following information:
Directions for submitting interpretations to ASME, the effective dates of addenda,
(Addenda becomes mandatory six months after issue.) and Code cases.
Section IX is used to qualify procedures and personnel.
The following welding processes are addressed by Section IX:
OFW
SMAW
SAW
GMAW
FCAW
GTAW
PAW
ESW
EGW
EBW
SW
Oxyfuel Welding
Shielded Metal Arc Welding
Submerged Arc Welding
Gas Metal Arc Welding
Flux Core Arc Welding
Gas Tungsten Arc Welding
Plasma Arc Welding
Electroslag Welding
Electrogas Welding
Electron Beam Welding
Stud Welding
Page 10 - 1
Section II, Part C is the part of Section II that describes welding materials. Section II,
Part C, describes:
The Processes that may be used with each electrode, recommended storage
information, an explanation of the AWS symbols, positions to be used with
electrodes and recommended polarity and current.
A welding procedure shows compatibility of:
Base metals
Filler metals
Processes
Technique
When writing a procedure, a good method to use would be to write a sample
procedure, weld a test coupon, prepare the test specimen and test them, evaluate
the results and document them on and certify the PQR. Considerations involved
when writing a procedure include:
Economy, the compatibility of the base and weld metal, metallurgical and
mechanical properties of the weld, heat treatment requirements, service
requirements, welder’s ability and equipment available.
The manufacturer must qualify the WPS, maintain the WPS and PQR while welding
is being performed and provide a listing of all procedures that may be used on code
items.
The code forms provided in Section IX are not mandatory, any form may be used
provided all the required variables are addressed.
The general approaches to procedure qualification is usually in one of two forms:
Prequalified procedures
These are AWS welding procedures used only for structural welding
and do not require testing. The user is limited to specific weld joints
and specific weld processes (see AWS D 1.1).
ASME Section IX, 2001 Edition, Paragraph QW-100.1 now allows AWS
Standard Welding Procedure Specifications (SWPS), as listed in
Appendix E or in accordance with Article V.
Procedure qualification testing
These are API and ASME requirements. Both require actual welding to
be performed and destructively tested.
ASME procedure qualification testing uses a listing of essential variables in the
creation of weld procedures. Essential variables are those in which a change is
considered to affect the mechanical properties of the weldment, and shall require
requalification of the WPS, ASME IX Paragraph QW - 251.2.
Under ASME rules the welding procedure begins with the creation of the WPS. This
information is taken from ASME IX and outlines the ranges of materials, electrodes
Page 10 - 2
and other general aspects. Then the PQR is created, performed and tested and used
as proof for the WPS. The WPS can have many supporting PQRs.
The basic steps in qualifying a WPS are as follows:
• Write a sample around construction parameters and Code variables (QW-250)
• Establish a test coupon size (QW-451)
• Weld the test coupon using the parameters established.
• Monitor all variables and record at least the essential variables on the PQR. If
notch toughness is a requirement, a supplementary essential variable must be
recorded.
• Cut the coupons into specimens (QW-462).
• Make the required tests per QW-451.
• Evaluate the results against the appropriate criteria found in Article I.
• If acceptable, certify the PQR
• Approve the WPS for use on Code piping or other Code applications.
• Release the approved WPS and PQR for production.
The required tests for procedure qualifications are described in QW-202. This
paragraph requires 2 tensile tests and 4 bend tests minimum for groove weld
qualification. Table QW-451 provides information on coupon size, ranges and test
requirements for groove weld qualification.
QW-451.1
GROOVE-WELD TENSION TESTS AND TRANSVERSE-BEND TESTS
Range of Thickness T
of Base Metal
Qualified, in.
[Note (1)]
Thickness t of Deposited
Weld Metal Qualified, in.
[Note (1)]
Type and Number of Tests Required
Tension and Guided-Bend Tests
[Note (4]
Thickness T of Test
Coupon Welded, in.
Min.
Max.
Max.
Tension Side Bend Face Bend Root Bend
QW-150 QW-160 QW-160 QW-160
Less than 1/16
T
2T
2t
2
...
2
2
1/16 to 3/8, include.
1/16
2T
2t
2
Note (3)
2
2
Over 3/8, but less than 3/4
3/16
2T
2t
2
Note (3)
2
2
3/4 to less than 1 1/2
3/4 to less than 1 1/2
3/16
3/16
2T
2T
2t when t < 3/4
2t when t > 3/4
2 (5)
2 (5)
4
4
...
...
...
...
1 1/2 and over
1 1/2 and over
3/16
3/16
8 (2)
8 (2)
2t when t < 3/4
8 (2) when t > 3/4
2 (5)
2 (5)
4
4
...
...
...
...
NOTES:
(1) See QW-403 (.2, .3, .6, .9, .10), QW-404.32, and QW-407.4 for further limits on range of thickness qualified.
Also see QW-202 (.2, .3, .4) for allowable exceptions.
(2) For the welding processes of QW-403.7 only; otherwise per Note (1) or 2T, or 2t, whichever is applicable.
(3) Four side-bend tests may be substituted for the required face- and root-bend tests, when thickness T is 3/8 in.
and over.
(4) For combination of welding procedures, see QW-200.4.
(5) See QW-151 (.1, .2, .3) for details on multiple specimens when coupon thicknesses are over 1 in.
Page 10 - 3
Locations of weld specimens from plate procedure qualification.
Page 10 - 4
Locations of weld specimens from pipe procedure qualification.
Page 10 - 5
Weld procedure specimens, guided bends are also used for welder qualification
tests.
Square
Tensile Specimens
Round
Guided Bends
Face
Root
Side
Page 10 - 6
The tests commonly required by ASME Section IX are:
Tensile
Bends
Face
Root
Side
Table QW -451 is the Procedure qualification thickness limits and test specimens
requirements. Each groove weld must pass tension tests and transverse bend tests.
This table is where the requirements for testing are listed..
After the procedure qualification testing the Welding Inspector must check
production welding to ensure welds are being made in compliance with the
approved and tested weld procedure. Remember the weld procedure is proof that
the weld can be successfully made.
The general sequence for procedure qualification testing is as follows:
• Select welding variables (write the WPS and PQR)
• Check equipment and materials for suitability
• Monitor weld joint fit-up as well as actual welding,
recording all important variables and
observations
• Select, identify and remove required test specimens
• Test and evaluate specimens
• Review test results for compliance with applicable
code requirements
• Release approved procedure for production
• Qualify individual welders in accordance with this
procedure
• Monitor production welding for procedure
compliance
Page 10 - 7
QW-482 SUGGESTED FORMAT FOR WELDING PROCEDURE SPECIFICATIONS
(WPS)
(See QW-200.1, Section IX, ASME Boiler and Pressure Vessel Code)
Company Name:
Welding Procedure Specification No.
Revision No.
Welding Process(es):
By:
Supporting PQR No.(s)
Date:
Date:
Type(s):
Automatic, Manual, Machine, or Semi-Auto
JOINTS (QW-402)
Joint Design
Backing (Yes)
Backing Material (Type)
Details
(No)
(Refer to both backing and retainers)
Metal
Nonmetalic
Nonfusing Meal
Other
Sketches, Production Drawings, Weld Symbols or Written Description should show the general arrangement of the parts to be
welded. Where applicable, the root spacing and the details of
weld groove may be specified.
(At the option of the Mfgr., sketches may be attached to illustrate joint design, weld layers and bead sequence, e.g., for
notch toughness procedures, for multiple process procedures,
etc.)
*BASE METALS (QW-403)
P-No.
Group No.
OR
Specification type and grade
to Specification type and grade
OR
Chem. Analysis and Mech. Prop.
to Chem. Analysis and Mech. Prop.
Thickness Range:
Base Metal:
Groove
Pipe Dia. Range:
Groove
Other:
to P-No.
Group No.
Fillet
Fillet
*FILLER METALS (QW-404)
Spec. No. (SFA)
AWS No. (Class)
F-No.
A-No.
Size of Filler Metals
Weld Metal
Thickness Range:
Groove
Fillet
Electrode-Flux (Class)
Flux Trade Name
Consumable Insert
Other
*Each base metal-filler metal combination should be recorded individually
Page 10 - 8
Sample Procedure
Using SMAW variables the following represents a sample welding procedure. This
procedure will be written under “ideal conditions”. The production information is
as follows:
•
A piping system is under construction using welding procedures qualified to
ASME Section IX.
•
The pipe wall is 1 inch thick.
•
The base material is SA-106-B.
•
Filler material will be F-3 for the root pass and F-4 for the fill.
•
There are no special service restrictions
The first part is general information supplied by the writer. a detailed sketch of the
joint should be included in the space provided or on attached sheets. (QW402.1)
«Base Metals
The P-No. is 1 to 1 (See QW-403.1)
The Specification, Type and Grade: SA 106 Grade B (Supplied Example)
Thickness Range: (QW-403.7 and QW-403.8)
Pipe Diameter Range: 2 7/8 inch Outside Diameter and over (QW-452.3)
«Filler Metals (QW-404.4)
SFA-5.1 &5.5 (QW-432)
AWS No. E-6010 (Supplied Example)
AWS No. E-7018 (Supplied Example)
F-No.: 3 (QW-432)
F-No.: 4 (QW-432)
Weld Metal Thickness Range: (QW-451.1)
Page 10 - 9
QW-482 (Back)
WPS No.
POSITIONS (QW-405)
Rev.
POSTWELD HEAT TREATMENT (QW-407)
Position(s) of Groove
Welding Progression: Up
Position(s) of Fillet
Temperature Range
Time Range
Down
GAS (QW-408)
PREHEAT (QW-406)
Percent Composition
Preheat Temp. - Min.
Interpass Temp. - Max.
Preheat Maintenance
Gas(es)
(Mixture)
Flow Rate
Shielding
(Continuous or special heating where applicable should be recorded)
Trailing
Backing
ELECTRICAL CHARACTERISTICS (QW-409)
Current AC or DC
Amps (Range)
Polarity
Volts (Range)
(Amps and volts range should be recorded for each
position, and thickness, etc. This information may
be listed in a tabular form similar to that shown below.
Tungsten Electrode Size and Type
(Pure Tungsten, 2% Thorated, etc.)
Mode of Metal Transfer for GMAW
(Spray arc, short-circuiting arc, etc.)
Electrode Wire feed speed range
TECHNIQUE (QW-410)
String or Weave Bead
Orifice or Gas Cup Size
Initial and Interpass Cleaning (Brushing, Grinding, etc.)
Method of Back Gouging
Oscillation
Contact Tube to Work Distance
Multiple or Single Pass (per side)
Multiple or Single Electrodes
Travel Speed (Range)
Peening
Other
Filler Metal
Weld
Layer(s)
Process
Class
Dia.
Current
Type
Polar
Amp
Range
Volt
Range
Travel
Speed
Range
Other
(e.g., Remarks, Comments,
Hot Wire Addition,Technique,
Torch Angle, Etc.)
Page 10 - 10
«Positions (QW-405.1)
Welding Progression: (QW-405.3)
«Preheat (QW-406.1) QW-407.1 Special requirements for preheating
«Postweld heat treatment (QW-407) none required
«Gas (QW-408) none required
«Electrical Characteristics (QW-409.4)
Current: DC
Polarity: DCRP
Amps: (QW-409.8)
«Technique (QW410.1)
String or Weave Bead: Stringer / Weave
Cleaning: (QW-410.5) Brush or grind as necessary
Method of Back Gouging: (QW-410.6) ACA-A or grind as necessary
Peening: (QW-410.26) None allowed
Page 10 - 11
QW-483 SUGGESTED FORMAT FOR PROCEDURE QUALIFICATION RECORD
(PQR)
(See QW-200.2, Section IX, ASME Boiler and Pressure Vessel Code)
Record Actual Conditions Used to Weld Test Coupon
Company Name
Procedure Qualification Record No.
WPS No.
Welding Process(es)
Types (Manual, Automatic, Semi-Auto.)
Date
JOINTS (QW-402)
Groove Design of Test Coupon
(For combination qualifications, the deposited weld metal thickness will be required for each filler metal or process used.)
BASE METALS (QW-403)
Material Spec.
Type or Grade
P. No.
Thickness of Test Coupon
Diameter of Test Coupon
Other
POST WELD HEAT TREATMENT (QW-407)
to P-No.
Temperature
Time
Other
GAS(QW-408)
Gas(es)
FILLER METALS (QW-404)
SFA Specification
AWS Classification
Filler Metal F-No.
Weld Meal Analysis A-No.
Size of Filler Metal
Other
Weld Metal Thickness
Percent Composition
(Mixture)
Flow Rate
Shielding
Trailing
Backing
ELECTRICAL CHARACTERISTICS (QW-409)
Current
Polarity
Amps.
Volts
Tungsten Electrode Size
Other
POSITION (QW-405)
TECHNIQUE (QW-410)
Position of Groove
Weld Progression (Uphill, Downhill)
Other
Travel Speed
String or Weave Bead
Oscillation
Multipass or Single Pass (per side)
Single or Multiple Electrodes
Other
PREHEAT (QW-406)
Preheat Temp.
Interpass Temp.
Other
Page 10 - 12
QW-483 (Back)
PQR No.
Tensile Test (QW-150)
Specimen
No.
Width
Thickness
Area
Ultimate
Total Load
lb.
Ultimate
Unit Stress
psi
Type of
Failure &
Location
Guided-Bend Tests (QW-160)
Type and Figure No.
Toughness Tests (QW-170)
Specimen
No.
Notch
Location
Notch
Type
Test
Temp.
Impact
Values
Lateral Exp.
% Shear
Mils
Drop Weight
Break
No Break
Fillet-Weld Test (QW-180)
Result- Satisfactory:
Macro - Results
Yes
No
Penetration into Parent Metal: Yes
No
Other Tests
Type of Test
Deposit Analysis
Other
......................................................................................................................................................
Welder’s Name
Tests conducted by:
Clock No.
Stamp No.
Laboratory Test No.
We certify that the statements in this record are correct and that the test welds were prepared, welded, and
tested in accordance with the requirements of Section IX of the ASME Code.
Manufacturer
Date
By
(Detail of record of tests are illustrative only and may be modified to conform to the type and number of test required by the Code.)
Page 10 - 13
ASME Section IX
Welder Qualification
Welder qualification establishes the skill level for the welder. The test positions are
similar to the welding procedure positions. The essential variables for welder
qualification are as follows:
Position
Joint Configuration
Electrode Type and Size
Process
•
•
•
•
Base Metal Type
Base Metal Thickness
Technique (Up-hill or Down-hill)
(d) 4G
(b) 2G
(a) 1G
(c) 3G
QW-461.3 Groove Welds in Plate -- Test Positions
(a) 1G Rotated
(b) 2G
(c) 5G
(d) 6G
QW-461.4 Groove Welds in Pipe -- Test Positions
Throat of weld
vertical
Axis of weld
horizontal
Axis of weld
vertical
Axis of weld
horizontal
45 deg.
(a) 1F
(b) 2F
(d) 4F
(c) 3F
QW-461.5 Fillet Welds in Plate - Test Positions
Page 10 - 14
PERFORMANCE QUALIFICATION - POSITION AND DIAMETER
LIMITATIONS
(Within the Other Limitations of QW-303)
Position and Type Weld Qualified [Note (1)]
Qualification Test
Weld
Position
Groove
Plate and Pipe
Over 24 in. O.D.
Plate - Groove
1G
2G
3G
4G
3G and 4G
2G, 3G and 4G
Special Positions m(SP)
Plate - Fillet
1F
2F
3F
4F
3F and 4F
Special Positions (SP)
F
F,H
F,V
F,O
F,V,O
All
SP,F
Fillet
Pipe
24 in. O.D.
Plate
and Pipe
F [Note (2)]
F,H [Note (2)]
F [Note (2)]
F [Note (2)]
F [Note (2)]
F,H [Note (2)]
SP,F
...
...
...
...
...
...
F
F,H
F,H,V
F,H,O
All
All
SP,F
...
...
...
...
...
...
F [Note (2)]
F,H [Note (2)]
F,H,V [Note (2)]
F,H,O [Note (2)]
All [Note (2)]
SP, F [Note (2)]
Position and Type Weld Qualified [Note (1)]
Qualification Test
Weld
Position
Groove
Plate and Pipe
Over 24 in. O.D.
Pipe - Groove [Note (3)] 1G
2G
5G
6G
2G and 5G
Special Positions (SP)
Pipe - Fillet [Note (3)]
1F
2F
2FR
4F
5F
Special Positions (SP)
F
F,H
F,V,O
All
All
SP,F
...
...
...
...
...
...
Fillet
Pipe
24 in. O.D.
Plate
and Pipe
F
F,H
F,V,O
All
All
SP,F
...
...
...
...
...
...
F
F,H
All
All
All
SP,F
F
F,H
F,H
F,H,O
All
SP,F
NOTES:
(1)
Positions of welding as shown in QW-461.1 and QW-461.2.
F = Flat
H = Horizontal
V = Vertical
O = Overhead
(2)
Pipe 2 7/8 in. O.D. and over.
(3)
See diameter restrictions in QW-452.3, QW-452.4 and QW-452.6
Page 10 - 15
The general sequence for Welder qualification testing is as follows:
• Identify essential variables
• Check equipment and materials for suitability
•
Check test coupon configuration and position
• Monitor actual welding, to assure that it complies with applicable
welding procedure
• Select, identify and remove required test specimens
• Test and evaluate specimens
• Complete necessary paperwork
• Monitor production welding
Page 10 - 16
QW-484 SUGGESTED FORMAT FOR MANUFACTURER’S RECORD OF WELDER OR
WELDING OPERATOR QUALIFICATION TESTS (WPQ)
See QW-301, Section IX, ASME Boiler and Pressure Vessel Code
Welder’s name
Clock no.
Stamp no.
Welding process(es) used
Type
Identification of WPS followed by welder during welding of test coupon
Base material(s) welded
Thickness
Manual or Semiautomatic Variables for Each Process (QW-350)
Actual Values Range Qualified
Backing (metal, weld metal, welded from both sides, flux, etc.) (QW-402)
ASME P-No.
to ASME P-No. (QW-403)
( ) Plate ( ) Pipe (enter diameter, if pipe)
Filler metal specification (SFA):
Classification (QW-404)
Filler metal F-No.
Consumable insert for GTAW or PAW
Weld deposit thickness for each welding process
Welding position (1G, 5G, etc.) (QW-405)
Progression (uphill/downhill)
Backing gas for GTAW, PAW or GMAW, fuel gas for OFW (QW-408)
GMAW transfer mode (QW-409)
GTAW welding current type/polarity
Machine Welding Variables for the Process Used (QW-360)
Actual Values
Range Qualified
Direct/remote visual control
Automatic voltage control (GTAW)
Automatic joint tracking
Welding position (1G, 5G, etc.)
Consumable insert
Backing (metal, weld metal, welded from back sides, flux, etc.)
Guided-Bend Test Results
Guided-Bend Tests Type
( )QW-462.2(Side) Results
( )QW-462.3(a) (Trans. R &F ) Type
( )QW-462.3(b) (Long R & F) Results
Visual examination results (QW-302.4)
Radiographic test results (QW-304 and QW-305)
(For alternative qualification of groove welds by radiography)
Fillet Weld - Fracture test
Length and percent of defects
Macro test fusion
Fillet leg size
in. x
in. Concavity/convexity
Welding test conducted by
Mechanical tests conducted by
Laboratory test no.
in.
in.
We certify that the statements in this record are correct and that the test coupons were prepared, welded and
tested in accordance with the requirements of Section IX of the ASME Code.
Organization
Date
By
Page 10 - 17
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Page 10 - 18
Welding Metallurgy
WELDING METALLURGY
Admixture: The interchange of filler metal and base metal during welding, resulting
in weld metal of composition borrowed from both. Limited admixture is necessary
to complete metallurgical union across the joint.
Aging: The recrystallization that occurs over an extended period of time, resulting
form austenite or other normally elevated-temperature structure being retained at a
temperature and under conditions where it has no permanent stability. The result
may be a change in properties or dimension. Under some circumstances, aging can
be advantageous.
Blowhole: A defect in metal caused by hot metal cooling too rapidly when
excessive gaseous content is present. Specifically, in welding, a gas pocket in the
weld metal, resulting from the hot metal solidifying without all of the gases having
escaped to the surface.
Crater cracks: Cracks across the weld bead crater, resulting form hot shrinkage.
Heat-affected zone: The portion of the base metal, adjacent to a weld, the structure
or properties of which have been altered by the heat of welding.
Hot shrinkage: A condition where the thin weld crater cools rapidly while the
remainder of the bead cools more slowly. Since metal contracts or shrinks as it
cools, and shrinkage in the crater area is restrained by the larger bead, the weld
metal at the crater is stressed excessively and may crack.
Lamination: An elongated defect in a finished metal product, resulting from the
rolling of a welded or other part containing a blowhole. Actually, the blowhole is
stretched out in the direction of rolling.
Pick-up: The absorption of base metal by the weld metal as the result of admixture.
Usually used specifically in reference to the migration of carbon or other critical
alloying elements from the base metal into the weld metal. Depending upon the
materials involved, this can be an asset and not a liability.
Segregation: The tendency of alloying elements, under certain heat conditions, to
separate from the main crystalline constituent during transformation and to migrate
and collect at the grain boundaries. There they often combine into undesirable
compounds.
Page 11 - 1
Stringers: The tendency of segregated atoms of alloying elements or their
compounds to attach to one another in thread-like chains.
The problems encountered in welding can be better understood through a basic
understanding of metallurgy. The metallurgical effects of welding are the effects of
heat. Whether the welds are made by a gas flame, a metal arc, or electrical
resistance, the effects on the parent metal are due to heat.
Every fusion welding operation involves a logical sequence of thermal or heat
events. These include:
1.
2.
3.
4.
Heating of the metal
Manipulation of the electrode or torch flame to deposit weld metal
Cooling of the weld deposit as well as the base metal
Reheating of the entire structure for stress-relieving purposes, in
some instances
In every weld, the metal immediately under the flame or arc is in a molten state; the
welded section is in the process of cooling off; and the section to be welded has not
yet been heated and so is comparatively cool. These various conditions are
encountered at the very same instant.
As a result of welding, the structure of the welded ferrous metal may become
martensitic, pearlitic or even austenitic in nature. The welder who knows
metallurgy can predict which structure will be found when the weld has cooled. It is
most important to know this because the final condition of the structure after
welding is the one that determines the strength, hardness, ductility, resistance to
impact, resistance to corrosion and similar mechanical and physical properties of the
metal. All these properties may be affected by conditions that exist during the
welding operation, so it is well to become acquainted with possible difficulties and
see how they may be avoided.
To avoid confusion, this discussion will be confined to steel. The effects of heating
and cooling will not necessarily be the same for the non-ferrous metals and alloys.
In some cases, a considerable difference in temperature ranges and other
characteristics exist.
The arc welding of steel involves very high temperatures. The resultant weld is
essentially cast steel. Since the base metal very close to the weld is comparatively
cool, a considerable variation in the grain structure develops within the weld area.
As the weld cools will alter the grain structure in both the weld itself and the
immediately adjacent base metal, known technically as the heat -affected zone.
Page 11 - 2
Danger from the Air
Unless extreme care to shield the weld metal is exercised during welding, the
possibility exists that oxygen or nitrogen or both will be absorbed from the air.
What either of these gases can do to weld metal is pitiful. An oxide or nitride
coating will form along the grain boundaries. Oxidation along the grain boundaries
greatly weakens the weld metal, and greatly reduces the impact strength and also
the fatigue resistance of the welded part. Nitrogen forms iron nitrides in chemical
composition with the iron, and these make the weld extremely brittle.
The extent to which oxides and nitrides penetrate a steel will depend upon the type
of steel, the temperature to which it is heated and the length of time it is held at this
temperature. Extreme care should be exercised to prevent the penetration of air
into high-temperature welding regions. The most satisfactory way to prevent oxide
or nitride contamination in metal-arc welding is to make sure that the electrode has
a coating that provides adequate shielding. The arc and weld metal may also be
shielded by carbon dioxide (CO2) or vapor. In gas tungsten arc welding (GTAW) or
gas metal arc welding (GMAW) (inert-gas-arc welding), the inert gas will provide
the shielding. With submerged-arc welding, the molten flux that covers the arc does
the job. Fluxes or a reducing flame provide the needed protection during gas
welding.
When the oxyacetylene torch is used for cutting, it is desirable to oxidize the steel. It
is rapid oxidation that makes it possible for the flame to sever steel.
Besides oxygen or nitrogen, another gas absorbed during welding may have
harmful effects on some types of metals and alloys. This gas is hydrogen, and
usually comes from moisture in the electrode coating or from the use of hydrogen
in the welding flame. The presence of hydrogen in the weld metal will weaken the
structure and lead to cracking of the weld. Hydrogen is a contributing cause of
underbead cracking. To avoid this harmful weld defect, use low-hydrogen
electrodes of the E-xx15, E-xx16 and E-xx18 series.
Heat-Affected Zone
A weld bead as deposited on the 1/2 inch plate produced a heat-affected zone that
extended for about 1/8 in. adjacent to the weld. This zone shows a variation in
grain structure adjacent to the weld. This zone shows a variation in grain structure
(staring at the bottom) from the normal base metal structure into a band of finer
grain structure between the lower and upper critical temperature points and then to
a coarse overheated grain structure adjacent to the weld.
The extent of the change in the grain structure depends upon the maximum
temperature to which the metal is subjected, the length of time this temperature
exists, the composition of the steel, and the rate of cooling. The cooling rate will not
only affect grain size but it will also affect physical properties.
As a rule, faster cooling rates produce a slightly harder, less ductile and stronger
steel. For low-carbon steels, the relatively small differences found in practice make
insignificant changes in these values. However, with higher carbon content in
appreciable amounts of alloying material, the effect may become serious.
Page 11 - 3
The speed of welding and the rate of heat input into the joint effects change in
structure and hardness. On a given mass of base metal, at a given temperature, a
small bead deposited at high speed produces a greater hardening than a larger bead
deposited at a higher heat input per unit length of joint. This is because small high
speed beads cool more rapidly than the larger high heat beads.
The effect that heat from welding has on the base metal determines to a great
degree the weldability of a metal and its usefulness in fabrication. A metal that is
sensitive to heat conditions or heat changes, as in the case of high-carbon and some
alloy steels, may require heat treatment both before and after welding.
Admixture or Pick-up
When a base metal is welded with a filler metal of different composition, the two
metals will naturally mix and blend together in the molten weld pool.
Consequently, the weld metal will be a mixture of two materials. it will not
necessarily be an average of them, however.
The amount of base metal picked up in the molten weld pool varies greatly relative
to the amount of deposited electrode metal. Some welds are made up principally of
base metal, while others are primarily deposited electrode metal. The specific
process of welding, the rate of electrode travel, the current selected, the width of the
joint, the base metal composition, the plate thickness -- all these factors determine
the volume of base metal brought to a molten temperature, and therefore the
amount of base metal pick-up or admixture into the weld.
In some cases, the deposited metal and the base metal are sufficiently alike in
composition that the amount of admixture is of little significance. At other times,
admixture is an advantage in that the weld metal is made stronger or otherwise
improved by a pick-up of carbon or other needed elements from the base metal.
Unfortunately, under some conditions alloying elements or chemical combinations
of the base metal tend to concentrate -- to precipitate, or to segregate during the
heating and cooling cycle and reform into stringers or other arrangements that
harden, embrittle, weaken or otherwise cause inferior welds. Sometimes, the
stringer itself is a source of weakness. At other times, the segregation of an element
or its loss into the slag or atmosphere "starves" the newly formed weld
microstructure of elements needed for certain physical properties.
In general, admixture should be limited unless the metals and the processes
involved justify a procedure that calls for a specific amount of pick-up. This is
discussed further in later chapters on the welding of specific metal groups. To
minimize the effects of pick-up, electrode coatings or fluxes are often treated with
alloying elements that bring the deposited metal up to the desired composition.
These alloying elements replace those that might be destroyed or lost to either
parent metal or weld metal during the high-temperature welding operation.
Page 11 - 4
Carbide Precipitation
Sometimes, because of rapid cooling, steels, particularly stainless steels, are not
given time to go through all of the temperature changes indicated in the iron-carbon
diagram. As a result, a concentration of the solid solution (austenite) is retained at a
temperature where it simply has no business existing. This being against nature, so
to speak, the dissolved elements will eventually recrystallize. This type of
recrystallization is known as aging. Suppose, however, the metal is reheated before
recrystallization can occur. In this event, the carbon will crystallize out of the
austenite as iron carbide. This phenomena is known as carbide precipitation.
Stainless steels of the nickel-chromium variety are austenitic in nature even at room
temperatures. When such steels are heated, as by welding operations, carbide
precipitation is apt to occur. The carbides, or carbon compounds, are chromium as
well as iron. When chromium is used up in this way, in chemical union with the
precipitated carbon, the remaining austenite is deficient in the chromium element.
The result is a serious reduction in the corrosion-resisting properties of the stainless
steel.
When the carbides are precipitated in stainless steel, they appear mainly at the grain
boundaries. If subjected to corrosion, the carbides along the grain boundaries will
be attacked readily. Severe corrosive conditions will cause the grains to lose their
coherence and the steel to fail.
In making a weld on stainless, there will always be a region some distance back
from the weld where the base metal will be at the exact temperature of the
precipitation range: 800-1500°F. Consequently, the stainless qualities of the
structure will be lost unless steps are taken to prevent precipitation.
Austenitic stainless steels may be stabilized against carbide precipitation by the
addition of elements known as stabilizers. Such elements are columbium and
titanium. These elements have a ready affinity for carbon; they will grab and hold
fast the carbon that might otherwise have been attracted to the chromium.
Moreover, both titanium and columbium carbide resemble stainless steel in having
high resistance to corrosion. Stabilized stainless steels, therefore, will not fail under
the combination of heat and corrosive attack. Austenitic stainless steels also are
available in several grades with extra low carbon (ELC). Since there is less carbon,
the possibility of chromium migration to the grain boundaries is minimized.
It is well to remember that the stabilized and ELC austenitic steels will resist carbide
precipitation. If the welded stainless is to be subjected to corrosive conditions,
particularly at elevated temperatures, the base metal should be a stabilized steel and
it should be welded with electrodes or filler rods that have also been stabilized.
Page 11 - 5
Crater Cracks
In some instances, both arc welds and gas welds develop crater cracks. These come
from hot shrinkage. The crater cools rapidly while the remainder of the bead is
cooling slowly. Since the crater solidifies from all sides toward the center, the
conditions are favorable to shrinkage cracks. Such crater cracks may lead to failures
under stress -- brittle failures since there is an inclination towards fracture without
deformation. The remedy is to manipulate the electrode to fill up the craters when
you are welding.
Blowholes, Gas Pockets and Inclusions
Other common welding defects known as blowholes, gas pockets and inclusions
involve problems of electrode manipulation rather than metallurgy. These
difficulties are created because of the welder's failure to retain the molten weld pool
for sufficient time to float entrapped gas, slag and other forms of material.
A blowhole or gas pocket represents a bubble of as in the liquid weld metal. A gas
pocket is one that did not reach the surface before the metal began to freeze.
Consequently, the gas remains entrapped in the solidified metal.
Some gases, particularly hydrogen, are absorbed by the molten metal and are then
given off as the metal beings to cool. If the metal is in a molten condition, the gas
bubbles make their way to the surface and disappear. If the bubbles are trapped in
the growing grains of solid metal, blowholes are the result.
Blowholes are particularly prevalent in steels high in sulphur. In this case the
entrapped gas is either sulphur dioxide or hydrogen sulphide, the hydrogen being
supplied from moisture, the fuel gas (in gas welding), the electrode coating or the
hydrogen atmosphere that surrounds the weld in atomic-hydrogen welding.
Blowholes may be minimized in the weld area by using a continuous welding
technique so that the weld metal will solidify continuously. Most welding operators,
through practice, learn to develop welding techniques that will produce a relatively
gas-free weld. One of the secrets of such a technique is to keep the molten weld
pool at the temperature necessary for the rapid release of absorbed gases. At the
same time an unbroken protective atmosphere must be provided over the pool.
Modern electrode coatings aid in this problem, for they contain scavenging elements
that cleanse the weld pool while it is in molten condition.
Inclusions of slag and other foreign particles in the weld present a type of problem
similar to gas pockets and blowholes. These inclusions tend to weaken the weld.
Slag is frequently entrapped because of the operator's failure to manipulate torch,
filler rod or electrode so as to maintain a molten condition long enough to float out
all the foreign material. Ordinarily, the liquid slag freezes and forms a protective
coating for the weld deposit. On some occasions, however, because of the force of
the flame or arc, it is blown into the molten weld pool. The pool freezes before the
slag particle or particles can float to the top, thus producing a defective weld.
Page 11 - 6
Slag inclusions are more common in welds made in the overhead position. The
lower density of the slag tends to keep it afloat on the weld pool. In overhead
welding, the weld pool first forms at the narrow part of the vee, which is uppermost
in the weld. Since the pool tends to drip if kept molten too long, the welder works
to have it solidify as rapidly as possible. As a result, inclusions are frequent. This
problem in overhead welding can be overcome by using gaseous, non-slagging
types of electrodes.
Faulty plate preparation contributes to slag inclusions. If edges of V-joints are
beveled at too steep an angle and the gap between plates is too small, the weld
metal bridges the gap and leaves a pocket at the root in which slag tends to collect.
If back of joint is accessible, slag can be removed by back gouging; however, if this
operation is omitted, the result is a defective weld. With a J-joint or U-joint,
improper arc manipulation may burn back the inside corners and form pockets that
can entrap slag or gases.
In repair of a broken surface, a groove along the break line should be burned out or
ground so as to provide clean surfaces properly angled and spaced. Failure to do so
may leave an overhang of base metal or an unfilled crack that can entrap slag or
gases.
Surfaces to be welded should be thoroughly cleaned of scale, dirt, paint, lubricants,
and other chemicals that might contribute to formation of gas or dirt inclusions in
the weld.
Welds that contain blowholes, gas pockets and inclusions may develop other defects
upon hot work. By the action of hot working, the basic defects are exaggerated to
form larger defects. For example, if a piece of weld metal containing a blowhole is
rolled, the tendency is to flatten and elongate the hole. This develops a long fibrous
defect running in the same direction as the piece that is rolled. Such a condition,
known as a lamination, will reduce the strength of the metal, particularly in directions
at right angles to the lamination.
Page 11 - 7
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Page 11 - 8
Technical Report Writing
TECHNICAL REPORT WRITING
LEGAL IMPLICATIONS
I.
Preamble Comments
A.
The completeness, factual data transmitted and final validity of any
equipment inspection depends on the depth and scope of the
officially submitted Inspection Report.
B.
The customer's perception of You as a qualified professional is
always strongly influenced by what is contained in the report.
Remember the "Image" comments earlier? Your report may well be
"the make or break" factor about whether you or your company will
be favorably considered for future inspection activities.
C.
An unknown factor usually exists relative to the "likes, dislikes and
preferences" of the person who receives or acts on your inspection
report. Some factors include:
1.
2.
3.
4.
5.
6.
D.
Organization of data
Length of report
Factual versus theoretical
Precise details or general statement.
Recommendations or suggestion.
Line-item coverage or report by exceptio.
When developing the Inspection Report, consider:
1.
2.
3.
Who will read and/or react to its contents, such as project
engineers, superintendents, managers, supervisors, foremen,
craftsmen, etc.?
Can the report be understood, or will a translator be needed?
If repair recommendations or sketches are submitted, how
much "hand-holding" is required for them to be understood?
Page 12 - 1
II.
Date and Signature
For a report to be auditable (legitimate by law), it must be dated and signed
by the inspector/person involved. Basically, any item worth reporting is
worthy of legal validation.
III.
Report Format/Descriptive Contents
A.
Many of those reading/reacting to your report simply do not have
time to attempt to grasp or correlate those items most useful to their
response. Therefore, the report should be factual, concise and
reasonably easy to grasp or understand.
B.
An "attention getter", up front statement is always helpful.:
NOTE:
C.
Remember that the person to whom you submit a report is a
Client. It may be an "in-house" client for those inspecting
equipment owned by their respective employer, or it may be a
contract-owner relationship.
Many, if not most, clients will not appreciate, nor perhaps even
tolerate, a report that contains "inflammatory" comments. In this
context, inflammatory words, comments, opinions or predictions
could be anything that, in the event of some future legal action, would
place the equipment owner in a precarious, defensive position. Some
examples are:
1.
2.
3.
4.
5.
Dangerous
Explosion
Hazardous
Health Problem
Unsafe
A simpler explanation would be any comment or wording that could be
twisted or used out of context by lawyers in a negligence trial situation.
Certainly, the comments listed above are not meant or intended to cause an
inspector to prostitute himself or his profession by "soft-pedaling" or ignoring
serious problems, plus informing the client whenever problems exist. Each
client deserves a true, factual evaluation and condition report. It is possible,
however, to structure your report comments in such a fashion that problems
can be stated (or client informed) so as to impart various degrees of urgency
or involving areas or component items requiring immediate or near term
corrective action.
Page 12 - 2
IV.
Report Vocabulary
A.
Each individual most probably has already established, or will
establish, his own vocabulary (or word usage) to identify or project his
evaluation of conditions noted during the inspection survey. Degrees
of corrosion/deterioration exist, plus varying stages or phases of
problems involving mechanical equipment, safety, environment, etc.,
must be described and/or commented upon. Some common
descriptive phrases/comments I have become comfortable with are
listed below. You will note that it is possible to make many
combination statements by grouping certain descriptive words into
comments that best describe your personal evaluation.
1.
2.
3.
4.
5.
6.
7.
B.
Very minor, general corrosion.
Minor to moderate, etc., etc.
Moderate, etc., etc.
Moderate to severe, etc., etc.
Severe, etc., etc.
The results of this inspection survey indicate that repair as
follows is recommended.
Inspection/evaluation of this equipment indicates it to be in
good condition and is considered OK for long term service.
Owner/client user Expectations
You are hired (or used) to determine existing conditions of equipment,
assess and evaluate the impact on future reliability, determine
corrosion/metal thickness limitations or minimum requirements.
You are expected to use your best judgment, expertise, experience and
training to develop (perhaps even to recommend), the most cost effective,
safest, operationally reliable method/degree of repair necessary to achieve
the above conditions.
V.
Report Structure
A.
Recall earlier comments regarding those who will receive your
report plus those who will eventually react to your comments and/or
recommendations.
Page 12 - 3
B.
Methods, data organization, component part separation, etc.,
suggested for your strong consideration include:
1.
Method of presentation
a.
Keep the report as brief( but complete) as possible or
practical.
b.
Keep it factual. If theorizing is required, make sure
that this approach is recognized.
c.
Avoid, whenever possible, inflammatory words or
comments.
d.
Be conscious of the economics involved. Don't
recommend complete item renewal, when 50%
renewal will provide the desired results.
2.
NOTE:
Data Organization/Component Part Separation
Do not intermingle comments/conditions. Keep comments
separated in the report body and on the repair items
recommended.
Ideally, repair items should be arranged in order, clearly
defined and explicit enough, that the list can be given to
maintenance personnel who can make proper repairs from
the list.
VI.
Review Comments
The following are "Basic" in nature, but occasionally can be flexible to fit
the needs of a particular situation:
A.
Do's
1.
2.
3.
4.
5.
Keep as brief as possible, but present all factual data. A wide
flexibility is necessary because of the range of comments
required to satisfy numerous conditions.
Provide suggestions or recommendations relative to repair if
the client requests. Sketches involving repair or procedure
details are a mark of competence.
Be conscious of the economics involved that could result
from your recommendations.
Arrange data in an orderly fashion, separated into
component parts for ease of reading and understanding.
Sign and date report.
Page 12 - 4
1
B.
Don'ts
1.
2.
3.
4.
5.
Use inflammatory word, statements or opinions.
Present a mass of data all intermingled in one statement.
Make it a practice to theorize or guess as to problem cause.
Present condition comments or data involving one major
piping component into the same statement as data is
presented on a completely different major component.
Diminish your competency or professional image by a failure
to submit a comprehensive, factual, readable report that will,
by itself, be a future auditable document.
Page 12 - 5
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Page 12 - 6