Welding Defects
&
Inspection
Welding Defects
Discontinuity / Flaw
• An interruption of the typical structure of a
material, such as a lack of homogeneity in
its mechanical, metallurgical, or physical
characteristics.
• A discontinuity or flaw is not necessarily a
defect.
Defect
• A flaw that renders a part or product
unable to meet minimum applicable
acceptance standards or specifications.
• The term designates rejectability.
Classification
•
•
•
•
•
•
Cracks
Cavities
Solid Inclusions
Incomplete Fusion or penetration
Imperfect shape or unacceptable contour
Miscellaneous defects
Cracks
Detection
Surface:
Visual examination, magnetic particle,
dye or fluorescent penetrant inspection
Internal:
Ultrasonic flaw detection, radiography
Cracks
Solidification Cracking
• Causes:
– Low melting constituents;
Sulphur, phosphorus or niobium
pick-up from parent metal
– Large depth/width ratio of weld
bead
– High arc energy and/or preheat
Hydrogen Induced HAZ Cracking
• Causes:
– Hydrogen
– Hard microstructure
– Residual stresses
– Low temperature
Lamellar Tearing
• Causes:
– Poor ductility in through-thickness
direction in rolled plate due to nonmetallic inclusions
– Occurs mainly in joints having
weld metal deposited on plate
surfaces
– Prior buttering of surface beneficial
for susceptible plate
Reheat Cracking
• Occurs in creep resisting and some
thick low alloy steels during post weld
heat treatment
• Causes:
– Poor creep ductility in HAZ
coupled with thermal stress
– Accentuated by severe notches
such as preexisting cracks, or
tears at weld toes, or unfused root
of partial penetration weld
– Heat treatment may need to
include low temperature soaking
– Grinding or peening weld toes after
welding can be beneficial
X 35
X 200
Cavities / Pores
Detection
Surface: Visual inspection
Internal: Ultrasonic flaw
detection, radiography
Worm Holes
• Resulting from the entrapment of
gas between the solidifying
dendrites of weld metal, often
showing ‘herringbone’ array ( B )
Uniformly
Distributed Porosity
Surface Porosity
Solid Inclusions
Detection: Normally revealed by
radiography
Types:
Slag, Flux
Oxide
Tungsten
Linear Slag Inclusions
• Cause:
– Incomplete removal of slag
in multi-pass welds often
associated with the
presence of undercut or
irregular surfaces in
underlying passes
Isolated Slag Inclusions
• Causes:
– Normally by the presence of mill
scale and/or rust on prepared
surfaces, or electrodes with
cracked or damaged coverings
– Can also arise from isolated
undercut in underlying passes of
multi-pass welds
Lack of Fusion and Penetration
Detection
–
ultrasonics or X-ray
–
magnetic particle, dye or fluorescent penetrant inspection
Cause
–
Incorrect weld conditions (eg. low current) and/or incorrect
weld preparation (eg. root face too large)
–
Both cause the weld pool to freeze too rapidly
Incomplete Joint Penetration
and Incomplete Fusion
Lack of side-wall fusion
Lack of root fusion
Lack of penetration
Lack of inter-run fusion
Imperfect Shape
Detection
All shape defects can be determined by visual
inspections
Misalignment
• Amount a joint is out of
alignment at the root
• Cause: Carelessness. Also
due to joining different
thicknesses (transition
thickness)
• Detection: All shape defects
can be determined by visual
inspections
Excessive Reinforcement
• Causes:
– Deposition of too much weld metal,
often associated with in adequate
weld preparation
– Incorrect welding parameters
– Too large of an electrode for the
joint in question
Excessive Penetration
• Causes:
– Incorrect edge preparation
providing insufficient support
at the weld root
– Incorrect welding conditions
(too high of current)
– The provision of a backing bar
can alleviate this problem in
difficult circumstances
Undercut and Overlap
Undercut
• Results from the washing away of edge
preparation when molten
• Causes:
– Poor welding technique
– Imbalance in welding conditions
Overlap
• Causes:
– Poor manipulative
technique
– Too cold a welding
conditions (current
and voltage too low)
UNDERFILL
Concavity
Root Concavity
Convexity
UNACCEPTABLE
WELD PROFILES
Miscellaneous Faults
Arc Strikes
• Cause:
– Accidental contact of an
electrode or welding torch
with a plate surface remote
from the weld
– Usually result in small hard
spots just beneath the
surface which may contain
cracks, and are thus to be
avoided
Spatter
• Causes:
– Incorrect welding conditions
and/or contaminated
consumables or preparations,
giving rise to explosions within
the arc and weld pool
– Globules of molten metal are
thrown out, and adhere to the
parent metal remote from the
weld
Different Zones in weldment:
WELD
TESTING
DESTRUCTIVE TESTING
TENSION
BEND
IMPACT
HARDNESS
TENSION &
BEND
TESTING
Types
• Tension Test
– Transverse
Tension
– Longitudinal
Tension
– All Weld Metal
• Bend Test
– Root Bend
– Face Bend
– Side Bend
– Transverse Bend
– Longitudinal Bend
Types of specimens
Tension Testing
Tension test specimen
All-Weld-Metal Tension Test
BEND TESTING
• Shows physical condition of the
weld Determines
• Ductility
• Fusion and penetration
1800 Bend Test
Face Bend Testing
Root Bend Testing
Side Bend Testing
Longitudinal Face Bend Testing
Longitudinal Root Bend Testing
Fillet Bend Testing
IMPACT
• CHARPY AND IZOD
• The measurement is the energy required
to break a specimen with a given notch
o
• 2mm depth at a 45 bevel
TEST MACHINE
CHARPY
IZOD
Fracture toughness testing
Compact Tension Test
HARDNESS TESTS.
• This gives the metals ability to show
resistance to indentation which show it’s
resistance to wear and abrasion.
• The tests are
–
–
–
Brinell
Rockwell
Vickers
MICROSCOPIC
• Used to determine
the actual structure of
the weld and parent
metal
MACROSCOPIC
• Examined using a
magnifying glass .
• magnification from 2
to 20 time.
• it will show up slag
entrapment or cracks
.
• polishing not as high
as micro.
Weldability Tests
(Cracking Tests)
Self-Restraint Tests
•Self-restraint tests utilize the restraint, or stress, within the specimen to cause weld
metal or base metal cracking.
•No external loading of the specimen occurs. The specimen is designed to produce
variable restraint on the weld joint, thus causing cracking.
Lehigh Restraint Test:
•Hot & Cold Crack Test
•a plate with slots machined into the sides and ends
•A groove weld joint is machined along the centerline of
the plate, and a single-pass weld is produced along this
groove.
•The restraint from the plate and slots produces a weld
with various levels of cracking.
•The level of
•Restraint is altered by changing the length of the slots
Keyhole Restraint Cracking Test (Hot and Cold Cracks).
•It is a simplified version of the Lehigh test. The specimen is welded along the
groove beginning at the open end and progressing toward the hole.
•This imposes a varying degree of restraint along the weld, with a maximum at the
hole and a minimum at the edge where welding commenced.
•Cracks form at the hole and extend outward to a point where the restraint is low
enough to arrest the crack growth. The crack length is the measure of crack
susceptibility
Hould croft Crack Susceptibility Test (Hot Crack Test).
•The Houldcroft crack susceptibility test utilizes a design
•similar to the Lehigh test, but the slots vary in length from one end of the specimen
to the other.
•The Houldcroft test was developed for sheet steels. No weld joint is machined into
the specimen, but rather a bead-on-plate, complete
•penetration weld (usually using the GTAW process) is made.
•Duplicate samples are produced, and the mean crack length of these specimens is
used as an index of hot crack susceptibility.
Tekken Test (Cold Crack Test).
The Y joint provides more restraint than the U- or double-U joint designs. In these
tests, preheat and welding parameters are varied to alter the stress state, rather
than changing the specimen design.
This test is used to evaluate HAZ cracks and underbead cracks.
Externally Loaded Tests
•Externally loaded tests involve the application of an external load to the specimen during weld
testing. This external load
•is typically varied to alter the stress state and thus the severity of cracking. This allows a more
quantitative measure of stress than can be obtained from the self-restraint tests.
Implant Test
•The implant test is used to evaluate hydrogen-induced cracking (HIC).
•A rod of the steel base metal to be tested is machined to the dimensions shown in the end of
the rod having either a circular groove or a helical groove machined into it.
•The rod is placed inside a hole in the center of a plate so the top of the rod is flush with the
top of the plate.
•A weld bead is made on the top surface of the plate and passes directly over the top of the
rod.
•By making the weld over the rod, the groove in the rod is thus located in the coarse-grained
HAZ, which is most susceptible to HIC.
•After welding (but within 60 s after weld completion), the test setup is placed in an
apparatus that places a tensile stress
•on the rod, and this is maintained for 24 h, or until the weldment fails. Numerous samples
are welded, then tested under
•different loads. The time to fail is plotted as a function of the loading stress. The crack
susceptibility of the base metal is
•measured by the degree to which the failure stress is reduced with time.
Implant Test
Varestraint Test (Hot Crack Test).
Varestraint Test (Hot Crack Test).
•It is the most common test used to evaluate hot crack sensitivity. In this test, one end of a
rectangular bar (typically 50 by 205 by 6.4 mm, or 2 by 8 by 14in.) is firmly mounted in a
fixed position while the opposite end is attached to a hydraulic or pneumatic plunger
•Gas-tungsten arc weld is produced on the top side of the plate, along its longitudinal
centerline, beginning at the unsupported end and moving toward the fixed end. When the
welding arc reaches a predetermined location over a die block, the plate is bent to conform
to the radius of the die block.
•This induces an augmented longitudinal strain on the welded surface of the specimen.
•Various die blocks with different radii can be used on samples of the same material to
characterize the strain level at which cracking begins.
•Typically, for alloy evaluation, a single die block of known radius is used which will
produce cracking in all samples.
•Hot cracks typically form radially along the trailing edge of the weld pool and in the HAZ.
•The Varestraint test also has been used to test the hot crack susceptibility of filler material.
•By depositing filler wire on a plate (for example, with the gas-metal arc welding process)
and then machining the specimen surface flush, a Varestraint test can be made using the
GTAW process.
•This method has been used to evaluate the effect of base metal-filler material
•dilution on hot crack susceptibility.
Spot Varestraint Test (Hot Crack Test).
he spot Varestraint test is a modification of the Varestraint test; it is sometimes
referred to as the TIG-A-MA-JIG test
In this test, a stationary welding torch is used to produce a gas tungsten arc spot
weld in the center of a rectangular sample.
The specimen size is typically 140 by 25 by 6.4 mm (5.5 by 1 by 0.25 in.).
After the weld is established for a predetermined time, the test specimen is forced
around a curved die block and the arc is extinguished.
Hot cracks or hot tears form radially around the weld pool in the HAZ.
The totalcrack length, maximum crack length, or strain level necessary to cause
cracking is used as the measure of crack sensitivity.
The spot Varestraint test is used mainly for evaluating susceptibility to HAZ hot
cracking or liquationcracking
Spot Varestraint Test (Hot Crack Test).