Welding Insp. - Difetti.pdf

8/13/2019 Welding Insp. - Difetti.pdf

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M S Rogers 19 Sep 02

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



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



Cap Undercut


10/46M S Rogers 19 Sep 02 M S Rogers Cap undercutRoot undercut



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



Overlap



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)



Crater Pipe

Crater pipe

Weld crater



Contour Defects



Contour Defects

Incomplete filled groove Poor cap profile

Excessive cap heightIncomplete filled groove+ Lack of sidewall fusion


17/46M S Rogers 19 Sep 02Incomplete filled grooveExcess cap reinforcement



Root Defects



Root Defects

Incomplete root fusion

Incomplete root penetration

Low Amps/voltsLarge Root face

Small Root GapFast Travel Speed

Incorrect Electrode Angle

Contamination



Root Defects

Lack of root fusion Lack of root Penetration


21/46M S Rogers 19 Sep 02 Lack of root fusionLack of root penetration



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



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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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



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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

Welding Insp. - Difetti.pdf

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