WELDING INSPECTION AND QUALITY CONTROL
Upon completion of this module you will be able to:
1. Identify the different inspection methods used in non
destructive testing.
2. The uses and the limitations of the different inspection
methods.
Common methods used in NDE
 Visual Inspection (VT)
 Magnetic Particle Inspection (MT)
 Liquid (Dye) Penetrant Inspection (PT)
 X-Ray inspection (RT)
 Ultrasonic testing (UT)
 Air or water pressure testing (LT)
VISUAL INSPECTION – VISUAL TEST (VT)
What is Visual Inspection?
A. NDT process – non destructive testing is the original term
used to identify a method of inspection that does not destroy a
product usefulness. Current terms include nondestructive
inspection (NDI) or nondestructive evaluation or examination
(NDE)
B. Examination with the eye – therefore you are only able to
DETECT SURFACE DISCONTINUITIES.
C. Most important and most extensively used NDE/NDI/NDT
method (before any NDT or DT be applied.)
II. Advantages
A. Usually inexpensive - the majority of expense will be in the
inspector’s wage.
B. Equipment is small and inexpensive – there’s a lot of
equipment to aid in visual inspection, but all small and
inexpensive.
I.
C. No powered required – this makes VT the most portable NDT
process.
D. Can avoid defects and costly repairs – by able to make
intermittent inspection
II. DISADVANTAGES
A. Requires training and experience –the inspector should be
familiar with all the welding process.
B. Must have a good eyes – the AWS requires 20-40 natural or
corrected distance acuity for a certified welding inspector.
C. May not detect internal defects – limited to surface
discontinuities only, but it might give indication of substance
indication. Then can be supplemented by some other NDT
method.
D. No permanent records – the inspector must maintain a written
log, supplemented by pictures, and tape recorded report.
E. Subject to human error – must spend adequate time to prevent
errors.
IV. Five steps of Visual Inspection.
A. Inspection practice – establish a definite procedure to insure
adequate and consistent coverage.
B. Inspection prior to welding
C. Inspection during welding
D. Inspection after welding
E. Marking and making repairs
V. Equipment required.
A. Flashlight – used to remove shadows when an extension lamp
can’t be used.
B. Magnifying glass – low power can be used with caution, if
allowed by customer or code.
C. Protective lenses – pocket viewer with proper shade lens to
watch the welding taking place.
D. Weld gage – are hand held measuring devices used to assist
during welding and for final inspection.
E. Hammer and chisel – to remove spatter or slag from weld prior
to inspection.
F. Temperature Indicating Devices – some method must be used
to determine the preheating, interpass and postheating
temperatures. Pyrometer and tempelstick or crayons are
commonly used.
G. Magnet – a magnet can be used to help determine a materila
type.
VI. Inspection Before Welding
A. Drawing – drawing are complete and accurate?
B. Position of welds – does the position called for correspond to
the procedure or specification? In vertical is direction of travel
correct?
C. Welding symbols – if they are used are they complete and
accurate?
D. Welding procedure – is the procedure complete and accurate
according to the code or specification?
E. Material
1. Did purchasing obtain the correct material such as base
metal type and size. The correct electrode type size and the
correct shielding gas type and grade.
2. Materials should be checked for defects. Base metal should
be checked rust, mill, scale, laminations or delaminations.
3. Is the material preparation correct and according to
procedure, such as angles and condition after preparation.
F. Assembly
1. Inspect for proper fit up, as this will prevent discontinuities
from occuring.
2. Jigs and fixtures will assure proper alignment. Make sure they
are clean and free spatter and not damaged.
3. The tack welds are only short welds, but the quality must be
the same as all other welds. The tack welds must be made
with the same electrodes that are used for the rest of the
welds.
4. Pre heat will be used to slow the cooling rate and prevent
distortion. The pre heat could be used prior to tacking and / or
prior to welding.
G. Equipment
1. Inspect the equipment for any damaged such as damaged
cables, damaged ground clamps, or electrode holders. Inspect
the arc voltage and amperage meters making sure they are
with in range.
VII. Inspection DURING welding.
A. Electrodes – inspect for usage of proper electrodes, types,
size and storage. Low hydrogen type must be stored in a
stabilizing oven.
B. Root pass – the first layer or root pass is the most important
and is particularly susceptible to cracking. Thicker material will
crack and will require more pre heat.
C. Subsequent passes – inspection of successive layers is
sometimes carried out with the assistance of workmanship
Standard. Check for contour or undercut as these are good places
for slag to be trapped. Check for proper cleaning between
passes as this can prevent slag entrapment.
D. Crater formation – make sure crater are filled as this are areas
where crack are easily formed.
E. Weld size and sequence – are the weld size according to the
print and is the layer and sequence according to the procedure?
The use of various gages will determine this.
VIII. Inspection After welding
A. The applicable code or standard – it will list acceptance
standards They will generally cover the following areas;
1. Weld size – use gages to check conformance to prints
2. Contour and finish – is the contour convex or concave, and
what was called for in print? Is finish smooth and free from
surface irregularities.
3. Cracks – the code or standard will state if any is acceptable
and what size.
4. Overlap – it is an indication of lack of fusion
5. Undercut – if allowed how much?
6. Spatter – what is excessive?
IX. Making repairs
A. When marking areas to be repaired the marking should be
positive and clear. It should be a method that is understood by
all involved, should be permanent enough to be evident after the
repair has been made and inspected, and the marking must not
damaged the part.
Visual Inspection (VT)
 Fillet gauges measure
 The “Legs”of the weld
 Convexity

(weld rounded outward)
 Concavity
 (weld rounded inward)
 Flatness
Liquid (Dye) Penetrant Inspection (PT)
 Liquid penetrant inspection uses colored or
fluorescent dye to check for surface flaws.
 PT will not show sub-surface flaws.
 PT can be used on both metallic and non metallic
surfaces such as ceramic, glass, plastic, and metal.
 PT dose not require the part to be Magnetized.
DYE PENETRANTS
 These are an aid to visual inspection
1. Cleaner Solvent
2. Penetrant
3. Developer
 Will only find surface defects
 Use correct type
Process Principle – 6 steps
1. Surface preparation
2. Penetrant application
3. Excess penetrant removal
4. Developer application
5. Inspection / evaluation
6. Post cleaning
DYE PENETRANTS
 Types


Red
Flouresant
 CAUTION


Oil based
Water washable
DYE PENETRANTS
DETECTION
II. Application:
a. Ferrous and non ferrous materials
b. Plastic and glass – ceramics-insulators-anything that is
nonporous
III. Advantages:
a. Low cost
b. Ease in application and interpretation – easy to apply and
interpret result, discontinuities readily visible and portable.
c. Less training time for applicator – easy process to learn.
IV. Limitations:
a. Detects discontinuities that is open to surface only
b. Can not be used on porous or absorbent materials
V. Safety
a. Ventilation – check for toxic fumes from testing materials.
Check for volatility -explosive or fire flash points
b. Fire safety – the test material maybe non flammable but the
propellant used with spray cans maybe extremely flammable.
VI. Types:
A. Fluorescent (type A) – a dye that emits visible light rays when
viewed under black light.
1. considered to be more sensitive than the visible type
2. must be viewed under ultraviolet (black light) in darkened
overall lighting conditions. More expensive because of
equipment required. Limited field use.
B. Visible (type B) – a brilliantly colored dye that is highly visible
under normal lighting conditions
1. Use normal lighting for inspection
2. considered to be less expensive.
3. Simplest to use.
4. Easy to use for field work
5. no electric power required
C. Dual sensitivity – works both fluorescent and visible.
VII. Application
A. Follow Approved Procedure
1. Clean and dry the surface.
- Solvent cleaner
2. Apply penetrant (brush, spray or dip) penetrant power comes
capillary action
3. Penetration time -minimum dwell time is 5-20 minutes
3. Remove excess penetrant.
- when using solvent type, put solvent on a cloth not on the
part
- excess penetrant will give false indications
4. Apply developer an allow developer dwell time per standard
or specification. A “rule of thumb” developer dwell time is
equal to one half penetrant dwell time.
- developer will tend to make discontinuities appear larger.
6. Inspect and examine – true indications are caused by penetrant
bleeding from actual discontinuities.
7. Clean if required – same as step 1.
VII. Liquid Penetrant Comparator
a. Ideal temperature range of the material to be tested is 60 ⁰F –
125⁰F. If the test must be done outside of this range, further
qualification maybe required.
b. Test block – to establish acceptability limits of contamination
and dilution to see if developer and penetrant are OK.
1. Plated panels – brass panels are plated with nickel and
chromium are bent to produce cracks.
2. steel test blocks – annealed type 201 0r 302 stainless steel.
Sandblasted on one side only with 100 mesh average size grit,
gun held at 18” at 60 psi to achieve velvety finish.
3. aluminum test blocks – type 2024 by heating to
975F and quenched to form cracks. Used to
check comparison for operating out of the
normal temperature range. Used also to qualify
penetrant if shelf is questionable.
c. Preparation for reuse – blocks should be
cleaned with solvent to remove all penetrant
from cracks and then heated to dry and also to
drive out any remaining solvent.
end
Magnetic Particle Inspection (MT)
 Magnetic Particle Inspection (commonly referred to as
Magnaflux testing) is only effective at checking for flaws
located at or near the surface.
 MT uses a metallic power or liquid along with strong
magnetic field probes to locate flaws. (Particles will align
along voids)
 MT can only be used on materials that can be magnetized.
It can not be used be used for nonmagnetic materials such
as Austenitic Stainless steel and aluminum.
Principle:
An electric current is allowed to flow in or an electromagnet
is applied to part of the specimen to cause magnetic flux to
flow in the specimen.
If a defect exist in the surface layer, it blocks the flux flow, so the
flux flow is directed around the defect while it partially leaks to
the air. The leaking flux forms a pair of magnetic poles, S and N,
on both sides of the defect.(as shown)
SN
SN
N
S
Fig. A
Since the magnetic poles have larger attractive force than the
surrounding material surface, magnetic particles are attracted
by and adhere to the magnetic poles while attracting each other.
As a result, a magnetic particle pattern wider than the defect is
formed on the surface around the defect.
Width of magnetic particle pattern
Width of defect
To enable the formation o a proper magnetic particle pattern for
defect indication, the orientation of the defect and magnetic field
must be taken into account.
Two methods of magnetizing the weld zone.
1. The YOKE method which uses an electromagnet
2. The PRODE method in which electrode are applied to the
specimen to allow current to flow in the specimen.
- not applicable to high tensile steel since it can form a short
circuit between specimen and electrodes causing a defect
resembling an arc strikes.
- effective to detecting defects not exposed but existing near
the surface.
Two types of magnetic particles:
1. Fluorescent type
2. Non fluorescent type
Methods of particle application:
1. Wet method – magnetic particles are dispersed by suspension
in water or kerosene and the suspension is applied to the
specimen surface.
2. Dry method –magnetic particle are dispersed in the surface of
the specimen.
MAGNETIC PARTICLE
• Mainly for surface
defects
• Some sub surface
defects can be found
• Only ferrous metal
Ultrasonic testing (UT)
 Ultrasonic testing (UT) is a method of determining
the size and location of discontinuities within a
component using high frequency sound waves.
 Sound waves are sent through a transducer into the
material and the shift in time require for their return
or echo is plotted.
 Ultrasonic waves will not travel through air therefore
flaws will alter the echo pattern.
ULTRA SONIC
oscilloscope
Advantages:
a. Time to inspect – fast response / ability to inspect
from one side.
b. B. Cost - $3,500.00 machine / $200.oo transducer
c. Portable with battery pack
d. Accuracy can locate small discontinuity
Limitations:
a. Equipment
b. Operator
c. Standards
d. Reports and records




Radiographic Test (RT)
Radiographic Test is a NDT that can detect surface and internal
discontinuities using electro magnetic radiation of short duration
by means of either
1. X-Ray
2. Gamma Ray
It is a wave of energy that will pass through most materials and
develop the negative image of what it passes through on film.
Both of these methods are a danger to health
1. An X-Ray- Is electronically produced in a vacuum tube.
2. Gamma Ray-are emitted by the atomic decay.
 Two Common Source of Gamma Rays.
 Cobalt 60
 Iridium 192
 3.FILM VIEWER
 Pictures taken are viewed as negatives will only give flat
image not in three dimensional darkened area must be used
for viewing.
X- RAY
X-RAY VIEWER
Pictures taken are
viewed as negatives
will only give flat
image not in three
dimensional
darkened area must
be used for viewing
Advantages:
 A Radiograph ( X-Ray picture) is a permanent record of a weld
used for quality inspection purposes
 RT inspections can reveal flaws deep within a component
Limitations:
1. The necessity to have access to both sides of the part being
radiographed
2. Unfavorable shape and orientation of some discontinuities.
3. Radiation Safety requirements for personal protection.
4. Tight Cracks, unless they are essentially normal to the
radiation beam.
5. Shallow tight surface cracks in thick sections usually can not
be detected at all, even when properly oriented.
6. Laminations are nearly impossible to detect because their
orientation does not permit sufficient differences in the amount
of radiation absorbed through the piece being examined to
show the defect on film.
Air or water pressure testing
(LEAK TEST)
 Pressure testing or leak testing can be performed with
either gasses or liquids.
 Voids that allow gasses or liquids to escape from the
component can be classified as gross (large) or fine
leaks.
 Extremely small gas leaks measured in PPM (parts per
million) require a “Mass Spectrometer” to Sniff for tracer
gases
APPLICATION OF A LOAD
 Used to test pressure vessels
 Pipe lines
 The item for testing is filled with water or oil it is then
pressurised using a pump
 A safety valve is set 1.5 to 2 times below the
working pressure.
PRESSURE TEST
Pressure Gauge
Pump
Test Specimen
Quiz time
 True or False ?
 Dye penetrate inspections can only be used on non
magnetic material.
 Answer: False
Quiz time
 True or False ?
 X-Rays can only be used to locate flaws at or near the
surface of a weld.
 Answer: False
Quiz time
 True or False ?
 Virtually all welds have flaws.
 Answer: True
Quiz time
 True or False ?
 Magnetic particle testing can only detect flaws at or
near the surface.
 Answer: True
Quiz time
 True or False ?
 Magnet particle testing can only be done on materials
that can be magnetized.
 Answer: True
Quiz time
 The letters NDE Mean ___________ ?
A: nondestructive inspection
B: nondestructive evaluation
C: nondisruptive evaluation
D: nondestructive examination
Quiz time
 The method most often used to check for leaks as
small as one part per million (PPM) from a gas line
or cylinder is the _________ Method ?
A: hydrostatic
B: mass spectrometer
C: soap suds bubble
D: scleroscope
Modern Welding
York County School of Technology