Welding Defects Presentation
Welding Defects Presentation
Welding Defects Presentation
Engr. Muhammad B
DEFECTS
A flaw or flaws that by nature or
accumulated effect render a part or
product unable to meet minimum
applicable acceptance standards or
specifications. The term designates
rejectability.
CRACKS
Longitudinal
Transverse
Crater
Underbead and Heat-affected zone
Hot
Cold or delayed
Precipitation Induced Cracks
Longitudinal Crack
Definition: A crack running in
the direction of the weld axis.
May be found in the weld or
base metal.
Cause: Preheat or fast cooling
problem. Also caused by
shrinkage stresses in high
constraint areas.
Prevention: Weld toward
areas of less constraint. Also
preheat to even out the
Transverse Crack
Definition: A crack running
into or inside a weld,
transverse to the weld axis
direction.
Cause: Weld metal hardness
problem
Prevention: Increase in
preheating or use of more
ductile material as filler
material.
Repair: Remove and Reweld
Crater Crack
Definition: A crack, generally
in the shape of an X which
is found in a crater. Crater
cracks are hot cracks
Cause: The center of the
weld pool becomes solid
before the outside of the
weld pool, pulling the center
apart during cooling
Prevention: Use crater fill, fill
the crater at weld
Underbead Crack
Definition: A crack in
the unmelted parent
metal of the HAZ.
Cause: Hydrogen
embrittlement
Prevention: Use Lo/Hi
electrodes and/or
preheat
Repair: Remove and
reweld
Hot Crack
Definition: A crack in the weld that occurs
during solidification
Cause: Micro stresses from weld metal
shrinkage pulling apart weld metal as it
cools from liquid to solid temp.
Prevention:
Preheat or use a
low tensile filler
material
Cold Crack
Definition: A crack
that occurs after the
metal has completely
solidified
Cause: Shrinkage,
Highly restrained
welds, Discontinuities
Prevention: Preheat, weld toward areas of
less constraint, use a more ductile weld
metal
Repair: Remove and reweld, correct
problem first, preheat may be necessary.
POROSITY
Single Pore
Uniformly Scattered
Cluster
Linear
Piping
Single Pore
Separated by at least their own
diameter along the axis of the weld
Cluster
Porosity
Typically viewed as a single large
discontinuity
Linear Porosity
being linear greatly affects the severity
of this discontinuity
Piping Porosity
Generally has special allowable limits
Porosity Prevention
preheat will help
eliminate
may need an
electrode with more
deoxidizers
Use run-on/run-off
taps
restart on top of
previous weld and
grind off lump
Inclusions
Nonmetallic solid material
embedded in the weld
metal.Types
Slag
Wagontracks
Tungsten
Slag Inclusions
Definition: Slag entrapped
within the weld
Cause: Low amperage,
improper technique, Trying to
weld in an area that is too
tight. Slow travel in Vertical
Down
Prevention: Increase amperage
or preheat, grind out tight
areas to gain access to bottom
of joint
Repair: Remove by grinding.
Wagon Tracks
Definition: Slang term for a groove
left at the toe of a root pass which
becomes filled with slag and is
trapped in the weld
Cause: The contour of the root pass
is too high, or the weld toe is not
bonded to the base metal
Prevention: Use proper technique to
deposit the weld root
Repair: Best repaired before applying
the hot pass. Carefully grind the root
pass face flat. be careful not to
Tungsten Inclusion
Definition: A tungsten particle
embedded in a weld. (Typically
GTAW only)
Cause: Tungsten electrode too
small, amperage too high, AC
balance on +, Upslope too high,
electrode tip not snipped, electrode
dipped into the weld pool or
touched with the fill rod, electrode
split.
Prevention: Eliminate the cause
Incomplete Penetration
Definition: When the weld
metal does not extend to
the required depth into
the joint root
Cause: Low amperage, low
preheat, tight root
opening, fast travel speed,
short arc length.
Prevention: Correct the
contributing factor(s).
Repair: Back gouge and
Incomplete Penetration
Lack Of Fusion
Definition: Where weld metal does not
form a cohesive bond with the base metal.
Cause: Low amperage, steep electrode
angles, fast travel speed, short arc gap,
lack of preheat, electrode too small,
unclean base metal, arc off seam
Prevention: Eliminate the potential
causes.
Repair: remove and reweld, being careful
to completely remove the defective area.
This is sometimes extremely difficult to
find.
Cont.
Excessive Penetration
Unacceptable protrusion of the rootbead
Current too high, travel speed too slow,
root gap too wide, root face too thin..
Excessive Penetration
Other Defects
Misalignment
Undercut
Underfill
Concavity or Convexity
Excessive reinforcement
Improper reinforcement
Arc Strikes
Spatter
Arc Craters
Misalignment
Definition: Amount a joint is out of
alignment at the root
Cause: Carelessness. Also due to
joining different thicknesses
(transition thickness)
Prevention: Workmanship.
Transition angles not to exceed 2.5
to 1.
Repair: Grinding. Careful on
surface finish and direction of grind
marks. Inside of Pipe /Tube difficult.
Undercut
Definition: A groove cut at the toe of the weld and left unfilled
Cause: High amperage, electrode angle, long arc length, rust
Prevention: Set machine on scrap metal. Clean metal before
welding.
Repair: Weld with smaller electrode, sometimes must be low
hydrogen with preheat. Sometimes must gouge first.
Underfill
Definition: The weld surface is below
the adjacent surfaces of the base
metal
Cause: Improper welding techniques
Prevention: Apply proper welding
techniques for the weld type and
position. Use stripper beads before
the cover pass.
Repair: Simply weld to fill. May require
preparation by grinding.
Excessive Concavity or
Convexity
Definition: Concavity or
convexity of a fillet weld which
exceeds the specified allowable
limits
Cause: Amperage and travel
speed
Prevention: Observe proper
parameters and techniques.
Repair: Grind off or weld on.
Must blend smoothly into the
base metal.
Excessive Reinforcement
Definition: Specifically defined
by the standard. Typically,
Reinforcement should be flush
to 1/16(pipe) or flush to 1/8
(plate or structural shapes).
Cause: Travel speed too slow,
amperage too low
Prevention: Set amperage and
travel speed on scrap plate
Repair: Remove excessive
reinforcement and feather the
weld toes to a smooth
transition to the base plate.
Cont. ..
Insufficient Reinforcement
Definition: Specifically defined by the standard.
Typically, Underfill may be up to 5% of metal thickness
not to exceed 1/32 as long as the thickness is made
up in the opposite reinforcement. Not applied to fillet
welds.
Cause: On root reinforcement - Too little filler metal will
cause thinning of the filler metal. In OH position, too
hot or too wide will cause drooping of the open root
puddle.
Prevention: Use proper welding technique. Use backing
or consumable inserts. Use back weld or backing.
Repair: Possibly simply increase the face
reinforcement. If backwelding is not possible, must
remove and reweld.
Arc Strike
Definition: A localized coalescence outside
the weld zone.
Cause: Carelessness
Prevention: In difficult areas, adjacent
areas can be protected using fire blankets.
Repair: Where applicable, arc strikes must
be sanded smooth and tested for cracks. If
found, they must be remove and repaired
using a qualified repair procedure and
inspected as any other weld.
OverLap
Spatter
Definition: Small particles of weld metal
expelled from the welding operation which
adhere to the base metal surface.
Cause: Long arc length, severe electrode
angles, high amperages.
Prevention: Correct the
cause. Base metal can
be protected with
coverings or hi-temp
paints.
Repair: Remove by
grinding or sanding.
Arc Craters
Definition: A depression left at the
termination of the weld where the
weld pool is left unfilled.
Cause: Improper weld termination
techniques
Repair: If no cracks exist, simply fill in
the crater. Generally welding from
beyond the crater back into the crater.
Conclusions
Welding defects have the capacity to seriously
affect the weld performance and weld life. Hence,
it becomes extremely important to detect these
quickly before the weld weld defect leads to any
damage. The modern methods of welding enable
us to make improved welds. Also, the rise of better
defect detection technologies has made the task
of finding defects much simpler than before.
We have to realize that welds do not need to be
totally perfect as that would be too costly and
would take a lot of time. They simply need to be
within the working limits so that any damage is
prevented.