Welding defects

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TECHNOLOGY
Copyright © 2005 TWI Ltd
WI 3.1
M.Rogers
Welding Imperfections
Course notes section reference 3
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Weld Defect ClassificationWeld Defect Classification
Defects can be grouped under three main
classifications
Planar Defects: linear from at least one dimension
• Cracks
• Lack of fusion
Linear Volumetric Defects: Linear in length with volume
• Slag lines
• lack of fusion with associated slag
• Piping.
Non-planar defects: rounded indications without significat length
• Slag inclusions
• Gas pores/blow holes.
• Other matallic and non-matallic inclusions

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Defects which may be detected by visual inspection
can be grouped under the following headings
Cracks
Solid inclusions
Surface and profiles
Misalignment (set-up
irregularities)
Gas pores and porosity
Lack of fusion
Mechanical damage
Parent material damage
Miscellaneous
Faults in Fusion WeldsFaults in Fusion Welds
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CracksCracks

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Classified by Shape
Longitudinal
Transverse
Branched
Chevron
Classified by Position
HAZ
Centreline
Crater
Fusion zone
Parent metal
Cracks that may occur in welded materials are caused
generally by many factors and may be classified by
shape and position, cracks are classed as planar.
CracksCracks
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Longitudinal parent metal crack
Longitudinal weld metal crack Lamellar tearing
Transverse weld metal crack
CracksCracks

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Transverse crack Longitudinal crack
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InclusionsInclusions

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Root piping
Cluster porosityGas pore
Blow hole
Herringbone porosity
Loss of gas shield
Damp electrodes
Contamination
Arc length too large
Damaged electrode flux
Moisture on parent material
Welding current too low
Gas pore <1.5mm Blow hole.>1.6mm
Gas CavitiesGas Cavities
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Root piping
Porosity
Gas CavitiesGas Cavities

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Cluster porosity Herringbone porosity
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Slag originates from welding
flux
MAG and TIG welding
process produce silica
inclusions
Slag is caused by
inadequate cleaning
Other inclusions include
tungsten and copper
inclusions from the TIG and
MAG welding process
Slag inclusions are defined as a non-metallic inclusion
caused by some welding process
Slag inclusions
Parallel slag lines Lack of interun
fusion + slag
Lack of sidewall
fusion with
associated slag
Solid InclusionsSolid Inclusions

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Solid InclusionsSolid Inclusions
Lack of interun fusion + slag
Lack of sidewall fusion + slag
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Elongated slag linesInterpass slag inclusions

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Lack of FusionLack of Fusion
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Incomplete filled groove
+ Lack of sidewall fusion
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2
1. Lack of sidewall fusion
2. Lack of inter-run fusion
Poor welder skill
Incorrect electrode
manipulation
Arc blow
Incorrect welding
current/voltage
Incorrect travel speed
Incorrect inter-run cleaning

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Lack of sidewall fusion + incomplete filled groove
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An imperfection at the toe or root of a weld caused by
metal flowing on to the surface of the parent metal
without fusing to it
Contamination
Slow travel speed
Incorrect welding technique
Current too low
OverlapOverlap

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Toe OverlapToe Overlap
Fillet weldFillet weld
Toe OverlapToe Overlap
Butt weldButt weld
OverlapOverlap
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Lack of root fusion
Incomplete root penetration
Low Amps/volts
Large Root face
Small Root Gap
Fast Travel Speed
Incorrect Electrode Angle
Contamination
Arc blow
Weld Root DefectsWeld Root Defects

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Lack of root fusion Incomplete root
Penetration
Weld Root DefectsWeld Root Defects
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Lack of root penetration Lack of root fusion

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Surface & ProfileSurface & Profile
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Incomplete filled groove Poor cap profile
Excessive cap height
Poor cap profiles and excessive
cap reinforcements may lead to
stress concentration points at
the weld toes and will also
contribute to overall poor toe
blend
Weld Profile DefectsWeld Profile Defects

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Poor Cap Profile & Poor Toe Blend
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Incomplete filled grooveExcess cap reinforcement

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Poor stop/starts
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Miscellaneous DefectsMiscellaneous Defects

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Spatter
Excessive current
Damp electrodes
Contamination
Incorrect wire feed speed
when welding with the MAG
welding process
Arc blow
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Accidental striking of the arc
onto the parent material
Faulty electrode holder
Poor cable insulation
Poor return lead clamping
Arc strike

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An irregular groove at the toe of a weld run in the
parent metal
Excessive amps/volts
Excessive travel speed
Incorrect electrode angle
Excessive weaving
Incorrect welding technique
Electrode too large
Cap & Root UndercutCap & Root Undercut
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Intermittent Cap Undercut
Cap UndercutCap Undercut

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Cap undercutRoot undercut
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Shrinkage groove
Insufficient weld metal
deposited in the root pass
Too fast a cooling rate during
the application of the root
bead pass
Poor welding technique
A shallow groove caused by contraction in the weld
metal along each side of the penetration bead
Weld Root DefectWeld Root Defect

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Concave root
Root gap too large
Excessive back purge pressure
during TIG welding
Excessive root bead grinding
before the application of the
second pass
A shallow groove, which may occur in the root of a butt weld
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Concave Root

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Excessive root penetration
Root faces too small
Root gap too large
Excessive amps/volts
Slow travel speed
Root penetration bead in excess in accordance with the
relevant specification being used
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Excessive root
penetration

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Concave root Excess root penetration
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High Amps/volts
Small Root face
Large Root Gap
Slow Travel Speed
Burn through
A localized collapse of the weld pool due to excessive
penetration resulting in a hole in the root run

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Burn Through
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Loss or insufficient back
purging gas
Most commonly occurs
when welding stainless
steels
Purging gases include
argon, helium and
occasionally nitrogen
Oxidized Root (Root Coking)Oxidized Root (Root Coking)

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Crater pipe
Weld crater
Crater PipeCrater Pipe
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Crater pipe is a shrinkage defect and not a gas defect, it
has the appearance of a gas pore in the weld crater
Too fast a cooling rate
Deoxidization
reactions and liquid to
solid volume change
Contamination
Crater cracks
(Star cracks)
Crater pipe
Crater PipeCrater Pipe

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Mechanical DamageMechanical Damage
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Mechanical damage can be defined as any surface material
damage cause during the manufacturing process.
This can included damage caused by:
Grinding
Hammering
Chiselling
Chipping
Breaking off welded attachments (torn surfaces)
Using needle guns to compress weld capping runs

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Mechanical Damage/Grinding Mark
Chipping Marks
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SetSet--up Irregularitiesup Irregularities

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A variation of leg lengths on a fillet weld
Note: Unequal leg lengths on a fillet weld may be specified
as part of the design, in which case it will not be
considered as a defect.
Unequal Leg LengthsUnequal Leg Lengths
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Plate/pipe Linear Misalignment
(Hi-Lo)
Angular Misalignment
Linear misalignment is
measured from the lowest
plate to the highest point.
Angular misalignment is
measured in degrees

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Linear Misalignment
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Linear Misalignment

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