Weld Defects and

Discontinuities

Richard M. Beldyk, PE, NSPE

AWS Certified Welding Engineer
AFE Certified Plant Engineer
Defect
• 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.
Discontinuity
• An interruption of the typical structure of
a material, such as a lack of homogeneity
in its mechanical, metallurgical, or
physical characteristics. A discontinuity is
not necessarily a defect.
Weld Joint Discontinuities
• Inclusions • Base Metal
• Misalignment (hi-lo)
• Slag
• Undercut Discontinuities
• Wagontracks
– Lamellar tearing
• Underfill • Tungsten
– Laminations and
• Concavity or Convexity • Spatter Delaminations
• Excessive reinforcement • Arc Craters – Laps and Seams
• Improper reinforcement • Cracks • Porosity
• Overlap • Longitudinal – Uniformly Scattered
• • Transverse
Burn-through – Cluster
• Crater
• Incomplete or – Linear
• Throat
Insufficient Penetration – Piping
• Toe
• Incomplete Fusion • Heat-affected zone
• Root
• Surface irregularity microstructure
• Underbead and
– Overlap Heat-affected zone alteration
• Arc Strikes • Hot • Base Plate laminations
• Cold or delayed • Size or dimensions
 Misalignment (hi-lo)

• 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.
Undercut
(cont......)

Undercut typically has an allowable limit.

Different codes and standards vary greatly
in the allowable amount.
Plate - the lesser of 1/32” or 5% (typ.)
 Insufficient Fill

• 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.
 Insufficient Fill on the Root
Side
(suckback)
• Definition: The weld surface is below the adjacent surfaces
of the base metal at the weld root.
• Cause: Typically improper joint preparation or excessive
weld pool heat.
• Prevention: Correct cause. (see next slide)

• Repair: Backweld to fill. May require removal of weld

section by grinding for access to the joint root.
 Cause for Insufficient Fill
at the Root

Some liquids, like water or molten steel, try to cover as much surface
area of whatever they are in contact with as possible.

Welding a root pass too wide can also cause the bead to sag (overhead
position).
 Removing a root pass by
grinding
1. Recreate the groove geometry as closely as possible.
2. Use a saw or die grinder and 1/16 - 1/8” cut off wheel to recreate root
opening. Remember repairs are sometimes required to be made with a
smaller electrode.
3. Open the groove angle. Be careful to leave the proper root face
dimension.
4. Feather the start and stop to blend smoothly into and out of the
existing weld.
 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.
Concavity
Convexity
 Reinforcement
The amount of a groove weld which extends beyond the surface
of the plate

• Excessive
Face Reinforcement
• Insufficient
• Improper
contour

Root Reinforcement
 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.
 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.
 Improper Weld Contour
• Definition: When the weld exhibits less than a 1350
transition angle at the weld toe. 1350

• Cause: Poor welding technique

• Prevention: Use proper techniques. A weave or whip

motion can often eliminate the problem.
• Repair: The weld face must be feathered into the base plate.
 Overlap

• Definition: When the face of the weld extends beyond the

toe of the weld
• Cause: Improper welding technique. Typically, electrode
angles and travel speed.
• Prevention: Overlap is a contour problem. Proper welding
technique will prevent this problem.
• Repair: Overlap must be removed to blend smoothly into
the base metal. Be careful of deep grind marks that run
transverse to the load. Also be careful of fusion
discontinuities hidden by grinding. Use NDT to be sure.
 Overlap
Overlap is measured with
a square edge such as a
6” rule. No amount of
overlap is typically
allowed.
 Burn-through (non-standard)

• Definition: When an undesirable open hole has been

completely melted through the base metal. The hole may or
may not be left open.
• Cause: Excessive heat input.

• Prevention: Reduce heat input by increasing travel speed,

use of a heat sink, or by reducing welding parameters.
• Repair: Will be defined by standards. Filling may suffice.
Otherwise, removal and rewelding may be required. Some
standards may require special filler metal and/or PWHT.
 Incomplete or Insufficient
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 back weld or remove and reweld.

 Incomplete 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.
 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.
Inclusions

• Slag
• Wagontracks
• Tungsten
 Slag Inclusion
• 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. Reweld.
 Wagon Tracks (non-standard)
• 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
gouge other areas on the weldment.
 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

• Repair: Grind out and reweld

Inclusions

• Fix when you see it. Otherwise grind out

& fix.
SLAG INCLUSION AT CORNER
BETWEEN BACKING BAR & PLATE
PROCESS - FCAW-g
Whiskers

• Unsightly
• Inhibits material flow in piping
• Are inclusions
• Can break off in pipes and damage
equipment downline
 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. Sometimes must be
tested as if it were a weld.
 Arc Craters

• Definition: A depression left at the termination of the weld

where the weld pool is left unfilled.
• Cause: Improper weld termination techniques

• Prevention:

• Repair: If no cracks exist, simply fill in the crater. Generally

welding from beyond the crater back into the crater.
Cracks
• Longitudinal
• Transverse
• Crater
• Throat
• Toe
• Root
• Underbead and Heat-affected zone
• Hot
• Cold or delayed
 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 cooling rates.
• Repair: Remove and reweld
 Transverse Crack
• Definition: A crack running into or inside a weld, transverse
to the weld axis direction.
• Cause: Weld metal hardness problem

• Prevention:

• Repair:
 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 termination
and/or preheat to even out the cooling of the puddle
• Repair:
 Throat Crack
• Definition: A longitudinal crack located in the weld throat
area.
• Cause: Transverse Stresses, probably from shrinkage.
Indicates inadequate filler metal selection or welding
procedure. May be due to crater crack propagation.
• Prevention: Correct initial cause. Increasing preheat may
prevent it. be sure not to leave a crater. Use a more ductile
filler material.
• Repair: Remove and reweld using appropriate procedure.
Be sure to correct initial problem first.
 Toe Crack
• Definition: A crack in the base metal beginning at the toe of
the weld
• Cause: Transverse shrinkage stresses. Indicates a HAZ
brittleness problem.
• Prevention: Increase preheat if possible, or use a more
ductile filler material.
• Repair:
 Root Crack
• Definition: A crack in the weld at the weld root.

• Cause: Transverse shrinkage stresses. Same as a throat

crack.
• Prevention: Same as a throat crack

• Repair:
 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: (only found using NDT). 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.

• Repair:
 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.
Repairs to Cracks

• Determine the cause

• Correct the problem
• Take precautions to prevent reoccurrence
• Generally required to repair using a
smaller electrode
Base Metal Discontinuities

• Lamellar tearing
• Laminations and Delaminations
• Laps and Seams
 Laminations

•Base Metal Discontinuity

•May require repair prior to welding
•Formed during the milling process
Lamination effects can be reduced by joint design:
Delaminations
 Laps and Seams

A mill-induced discontinuity in which results from a lump of metal

being squeezed over into the surface of the material.
If beyond acceptable limits, must be removed and repaired or
discarded.
Porosity

• Single Pore
• Uniformly Scattered
• Cluster
• Linear
• Piping
Single Pore

• Separated by at least their own diameter

along the axis of the weld
SINGLE PORE
Uniformly Scattered
Porosity

• Typically judged by diameter and

proximity to a start or stop
• often caused by low amperage or short
arc gap or an unshielded weld start
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

• 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
Heat-affected zone
microstructure alteration

• add drawing of HAZ of groove weld with

leaders to:
• grain refinement
• grain growth
• hardened areas
• softened areas
• precipitate susceptible areas.
Size or dimension

• If it renders the part unusable, it is a

defect.
• If it is outside the allowable limit, it
renders the part unusable.
• Things don’t have to be perfect, just within
the acceptable tolerance. Working to
perfection is too time consuming and
costly
Hammer marks

• Stress risers
• Unsightly
• Unnecessary
REPAIR TECHNIQUES

• May involve:
• different process
• different procedure
• different preheat/PWHT
• different electrode
• smaller electrode
Inspection Tools
 Measuring Weld Sizes
Fillet Weld Size - For equal leg fillet welds, the leg lengths of the
largest isosceles right triangle that can be inscribed within the fillet weld
cross section. For unequal leg fillet welds, the leg lengths of the largest
right triangle that can be inscribed within the fillet weld cross section
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Fibre Metal Fillet Gage
Undercut Gauge

Gal Gage Co.

Palmgrin Gauge
Magnifying Glass

Used to read small scales

 Flashlight
Used to cast shadows to find porosity, undercut and overlap.