welding insp. - difetti.pdf
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Welding Inspection Defects/Repairs
Course Reference WIS 5
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Weld Defects Defects which may be detected by visual
inspection can be grouped under five headingsCracks
Surface irregularities
Contour defects
Root defects
Miscellaneous
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Weld Defects
Other associated defectsCavities
Solid inclusions
Set up irregularities
Parent material defects
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Cracks
Hydrogen (HICC)
Solidification (Hot tears)
Reheat cracks
Lamellar tearing
The four essential crack mechanisms
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Cracks
Longitudinal parent metal crack Transverse weld metal crack
Longitudinal weld metal crack Lamellar tearing
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M S Rogers 19 Sep 02Transverse crack Center line crack
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Surface Irregularities
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Undercut An irregular groove at the toe of a weld run in
the parent metalExcessive amps/volts
Excessive travel speed
Incorrect electrode angle
Excessive weaving
Incorrect welding technique
Electrode too large
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Cap Undercut
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10/46M S Rogers 19 Sep 02 M S Rogers Cap undercutRoot undercut
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Overlap An imperfection at the toe or root of a weld caused by
metal flowing on to the surface of the parent metalwithout fusing to it
Contamination
Slow travel speed
Incorrect welding
techniqueCurrent too low
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Overlap
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Crater Pipe 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
Deoxidizationreactions and liquid tosolid volume change
ContaminationCrater crack(Star crack)
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Crater Pipe
Crater pipe
Weld crater
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Contour Defects
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Contour Defects
Incomplete filled groove Poor cap profile
Excessive cap heightIncomplete filled groove+ Lack of sidewall fusion
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17/46M S Rogers 19 Sep 02Incomplete filled grooveExcess cap reinforcement
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Root Defects
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Root Defects
Incomplete root fusion
Incomplete root penetration
Low Amps/voltsLarge Root face
Small Root GapFast Travel Speed
Incorrect Electrode Angle
Contamination
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Root Defects
Lack of root fusion Lack of root Penetration
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21/46M S Rogers 19 Sep 02 Lack of root fusionLack of root penetration
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Concave root
Root Defects
Root faces too large
Root gap too large
Excessive back purgepressure during TIG welding
Excessive root bead grindingbefore the application of thesecond 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 Defects
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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M S Rogers 19 Sep 02 Concave root Excessive root penetration
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Shrinkage groove
Root Defects
Insufficient weld metaldeposited in the rootpass
Too fast a cooling rateduring the application ofthe root bead pass
Poor welding technique
A shallow groove caused by contraction in the weldmetal along each side of the penetration bead
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Root Defects
Burn through
High Amps/volts
Small Root face
Large Root Gap
Slow Travel Speed
A localized collapse of the weld pool due to excessivepenetration resulting in a hole in the root run
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M S Rogers 19 Sep 02 Burn through
BurnThrough
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Root Coking/Oxidized RootLoss or insufficientback purging gas
Most commonly
occurs when weldingstainless steels
Purging gasesinclude argon, heliumand occasionallynitrogen
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Miscellaneous Defects
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Miscellaneous Defects
Arc strike
Accidental striking ofthe arc onto the parentmaterial
Faulty electrode holder
Poor cable insulation
Poor return leadclamping
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Spatter
Excessive current
Damp electrodes
Contamination
Incorrect wire feedspeed when weldingwith the MAG weldingprocess
Miscellaneous Defects
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Inclusions
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Gas Cavities
Cluster porosityGas pore
Blow holeHerringbone porosity
Root piping
Loss of gas shieldDamp electrodes
Contamination
Arc length too large
Damaged electrode flux
Moisture on parentmaterial
Welding current to low
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Gas Cavities
Root piping
Porosity
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M S Rogers 19 Sep 02 Single gas poreCluster porosity
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Solid Inclusions
Slag originates from weldingflux
MAG and TIG weldingprocess produce silicainclusions
Slag is caused byinadequate cleaning
Other inclusions includetungsten and copperinclusions from the TIG andMAG welding process
Lack of sidewallfusion with
associated slag
Slag inclusions
Parallel slag lines
Slag inclusions are defined as a non-metallic inclusion
caused by some welding process
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M S Rogers 19 Sep 02 Elongated slag linesInterpass slag inclusions
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Set-up Irregularities
Plate/pipe Linear Misalignment(Hi-Lo)
Poor fit-up
Angular Misalignment
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Linear Misalignment
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Parent Material Defects A welding inspector should also inspect the parent
material for any visible defects
Lamination
Mechanical damage Lap
Segregation line
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Plate Lamination
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Weld Repairs
W ld R i
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A weld repair may be used to improve weld profiles
or extensive metal removalRepairs to fabrication defects are generally easierthan repairs to service failures because the repairprocedure may be followedThe main problem with repairing a weld is themaintenance of mechanical properties
During the inspection of the removed area prior towelding the inspector must ensure that the defectshave been totally removed and the original jointprofile has been maintained as close as possible
Weld Repairs
W ld R i
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The specification or procedure will govern howthe defective areas are to be removed. The
method of removal may beGrinding
Chipping
Machining
Filling
Arc air gouging
Oxy-gas gouging
Weld Repairs