weld disconti

8/7/2019 weld disconti

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WELDWELD

DISCONTINUTIESDISCONTINUTIESByBy

YADAV VISHAL FULCHANDYADAV VISHAL FULCHAND

INSPECTION ENGINEERINSPECTION ENGINEERMANGALORE REFINERY AND PETROCHEMICALS LIMITEDMANGALORE REFINERY AND PETROCHEMICALS LIMITED


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WHAT IS DISCONTINUTITY?WHAT IS DISCONTINUTITY?

AWS D 1.1AWS D 1.1--9696

An interruption of the typical structure of a material such asAn interruption of the typical structure of a material such aslack of homogeneity in its mechanical ,or physicallack of homogeneity in its mechanical ,or physical

characteristics.characteristics.

A discontinuity is an objective lack of material, anA discontinuity is an objective lack of material, aninterruption in the physical consistence of a part.interruption in the physical consistence of a part.

Examples are cracks, seams, laps, porosity or inclusions.Examples are cracks, seams, laps, porosity or inclusions. It may or may not be considered a defect depending ifIt may or may not be considered a defect depending if

its presence endangers or not the integrity, the usefulnessits presence endangers or not the integrity, the usefulnessand the serviceability of the structure.and the serviceability of the structure.


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WHAT IS WELDING DEFECT?WHAT IS WELDING DEFECT?AWS D 1.1AWS D 1.1--9696

A discontinuity or discontinuities that by a nature orA discontinuity or discontinuities that by a nature oraccumulated defect (e.g. total crack length) render aaccumulated defect (e.g. total crack length) render apart or a product unable to meet the minimumpart or a product unable to meet the minimumacceptance standard or specificationsacceptance standard or specifications

They areThey are excessiveexcessive conditions, outside theconditions, outside theacceptance limits, which risks to compromise theacceptance limits, which risks to compromise thestability or the functionality of the welded structure.stability or the functionality of the welded structure.

They are also calledThey are also called rejectablerejectable discontinuities.discontinuities.

This means that the same type of discontinuity of aThis means that the same type of discontinuity of alesser degree, might be considered harmless andlesser degree, might be considered harmless and

acceptable.acceptable.


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This means DISCONTUITY is not a defect if itThis means DISCONTUITY is not a defect if itis acceptable within the limitation of applicableis acceptable within the limitation of applicablecodes and standards.codes and standards.

Whereas DEFECT is definitely discontinuityWhereas DEFECT is definitely discontinuityand defines rejectability of a part or product.and defines rejectability of a part or product.

Defects are otherwise called as Flaw or

Imperfections that are to be repaired so that thematerial is made more homogeneous as assumedin the design


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Influence of Discontinuities :Influence of Discontinuities :

They act as STRESS RAISERS.They act as STRESS RAISERS.

They reduce the cross sectional area and therebyThey reduce the cross sectional area and thereby

INCREASES STRESS CONCENTRATIONINCREASES STRESS CONCENTRATIONaround them.around them.

They provide a leak path.They provide a leak path.

They are potential site for CRACK initiation.They are potential site for CRACK initiation. They act as potential site for CORROSION &They act as potential site for CORROSION &

EROSION.EROSION.


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Characteristics of Discontinuities:Characteristics of Discontinuities:

Shape.Shape.

Acuity, sharpness or notch effect.Acuity, sharpness or notch effect.

Orientation with respect to principal workingOrientation with respect to principal workingstress and residual stress.stress and residual stress.

Location with respect to weld.Location with respect to weld.


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Production without Defects helps in:Production without Defects helps in:

Save work timeSave work time

Material repair costMaterial repair cost Decrease in ProductivityDecrease in Productivity


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Significance of defects depends on:Significance of defects depends on:

Microstructure in which defect occurs.Microstructure in which defect occurs.

Mechanical properties of the material.Mechanical properties of the material.

Type of loading (static, cyclic or shock)Type of loading (static, cyclic or shock) The environment (corrosive or non corrosive)The environment (corrosive or non corrosive)

Section thicknessSection thickness

Type and size of defectType and size of defect Stress pattern local to the defect.Stress pattern local to the defect.


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Classification of Discontinuities:Classification of Discontinuities:

Broadly classified into:Broadly classified into:

Planner defects or TwoPlanner defects or Two--dimensional defectsdimensional defects

e.g. crack, lack of fusion ,lack of penetration,e.g. crack, lack of fusion ,lack of penetration,lamination etc.lamination etc.

Voluminar defects or ThreeVoluminar defects or Three--dimensional defectsdimensional defects

e.g. Porosity, Inclusions etc.e.g. Porosity, Inclusions etc.


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Classification based on weldingClassification based on welding

process and procedure related:process and procedure related: GEMOMETRIC DISCONTINUTIESGEMOMETRIC DISCONTINUTIES

Misalignment, Undercut, Convexity & Concavity,Misalignment, Undercut, Convexity & Concavity,Excessive reinforcement, IncompleteExcessive reinforcement, Incompletereinforcement, Lack of Penetration, Lack ofreinforcement, Lack of Penetration, Lack offusion, Burn through, Overlap, Surfacefusion, Burn through, Overlap, Surfaceirregularity etc.irregularity etc.

OTHERSOTHERSArc strikes, Slag inclusions, Tungsten inclusions,Arc strikes, Slag inclusions, Tungsten inclusions,

Spatter, Arc craters, Oxide films etc.Spatter, Arc craters, Oxide films etc.


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Classification based onClassification based on

Metallurgical:Metallurgical: Cracks or fissuresCracks or fissures

Hot crack, cold crack, Lamellar tear etc.Hot crack, cold crack, Lamellar tear etc.

PorosityPorositySpherical, Elongated worm holes etc.Spherical, Elongated worm holes etc.


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POROSITYPOROSITY

It is a cavity type discontinuity (void) formed byIt is a cavity type discontinuity (void) formed by

gas entrapment during solidification.gas entrapment during solidification.

Gases present in weld environmentGases present in weld environmentHH22,N,N22,O,O2,2,CO,COCO,CO22 etc from flux coveredetc from flux coveredelectrodes.electrodes.

These gases trapped during solidification andThese gases trapped during solidification andcause porositycause porosity


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PorosityPorosity


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Classification ofPorosity:Classification ofPorosity:

According to its shape, size and location:According to its shape, size and location:

Uniformly scatteredUniformly scattered

Cause: Faulty material or poor technique usedCause: Faulty material or poor technique usedthought the weld.thought the weld.

Clustered (localized) porosity.Clustered (localized) porosity.

Cause: Improper termination/initiation of weld.Cause: Improper termination/initiation of weld.


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Classification ofPorosity:Classification ofPorosity:

Linear (aligned) porosityLinear (aligned) porosity

Porosity occur in a repetition pattern along thePorosity occur in a repetition pattern along the

weld usually associated with root or inter pass inweld usually associated with root or inter pass inconnection with LOP/LOF.connection with LOP/LOF.

CAUSE: Chemical reaction at weld jointCAUSE: Chemical reaction at weld joint

boundary,which produces unwanted gas.Thisboundary,which produces unwanted gas.Thiscan be avoided by preparing the joint properly.can be avoided by preparing the joint properly.


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Wormhole (Elongated porosity)

Elongated or tubular cavities caused by continuedElongated or tubular cavities caused by continuedentrapment of gases at the solidifying interfaceentrapment of gases at the solidifying interface

e.g. piping porosity, herringbone, solidificatione.g. piping porosity, herringbone, solidificationporosity.porosity.

It extend from weld root towards surface & is alsoIt extend from weld root towards surface & is also

evidence of the presence of surfaceevidence of the presence of surfacecontaminations.contaminations.


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Factors promoting porosity:Factors promoting porosity: Improper coating on the electrode.Improper coating on the electrode.

Longer arcs.Longer arcs.

Faster arc travel speeds.Faster arc travel speeds.

Too low and too high arc currents.Too low and too high arc currents. Incorrect welding technique (stringer beads areIncorrect welding technique (stringer beads are

more apt than moderately weaved beads.more apt than moderately weaved beads.

Unclean job surface.Unclean job surface.

Improper base metal composition (e.g. high SImproper base metal composition (e.g. high SC content will lead to porosity)C content will lead to porosity)


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POROSITY REMDIES:POROSITY REMDIES:

Use low hydrogen welding process, filler metalsUse low hydrogen welding process, filler metalshigh in deoxidizers for excessive H2,N2high in deoxidizers for excessive H2,N2atmosphere.atmosphere.

Use preheat or increase heat input to combatUse preheat or increase heat input to combathigh solidification rate.high solidification rate.

Clean joint surfaces and adjacent surfaces.Clean joint surfaces and adjacent surfaces.

For reducing excessive moisture useFor reducing excessive moisture userecommended procedure for baking and storingrecommended procedure for baking and storingelectrodeselectrodes


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POROSITYPOROSITY


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Radiograph:PorosityRadiograph:Porosity


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Radiograph:Cluster porosityRadiograph:Cluster porosity


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POROSITY SIGNIFICANCEPOROSITY SIGNIFICANCE

Less than 3 % by volume has an insignificant effect on staticLess than 3 % by volume has an insignificant effect on statictensile yield strengthtensile yield strength

Ductility is affected moreDuctility is affected more Higher the yield of the weld more isHigher the yield of the weld more isthe effectthe effect

Hydrogen Pore may act as a crack initiator in the weld.Hydrogen Pore may act as a crack initiator in the weld.

When the surface is ground the effect of surface pores becameWhen the surface is ground the effect of surface pores becamesignificantsignificant

In fillet welds, stress concentration effects of weld toes, startsIn fillet welds, stress concentration effects of weld toes, starts

and stops were significant. Internal porosity does not affect theand stops were significant. Internal porosity does not affect thefatigue strengthfatigue strength

Surface porosity indicates the loss of process control duringSurface porosity indicates the loss of process control duringweldingwelding


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CRACKSCRACKS

A CRACK is a fissure produced in a metal byA CRACK is a fissure produced in a metal by

tearing action.tearing action.

TYPES OF CRACKESTYPES OF CRACKES Hot crack/Solidification crackHot crack/Solidification crack

Cold crack.Cold crack.

Lamellar Tearing.Lamellar Tearing.


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CRACKSCRACKS


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CRACKSCRACKS


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TYPES OF CRACKING


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Cracks further classified into:Cracks further classified into:

Direction with respect to longitudinal axis of theDirection with respect to longitudinal axis of the

weld.weld.

Longitudinal crack:Longitudinal crack:Those lying in a directionThose lying in a directionparallel to the longitudinal weld axis.parallel to the longitudinal weld axis.

Transverse crack:Transverse crack:Those lying in a directionThose lying in a direction

perpendicular to the longitudinal weld axis.perpendicular to the longitudinal weld axis.


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Cracks classification:Cracks classification:

With respect to their locations:With respect to their locations:

Throat crack:Throat crack:

Root Crack:Root Crack: Toe Crack:Toe Crack:

Crater Crack.Crater Crack.

HAZ crack.HAZ crack. Base metal crack.Base metal crack.


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Hot CracksHot Cracks

Cracks formed immediately after welding.Cracks formed immediately after welding.

Also called centerline or solidification crack.Also called centerline or solidification crack.


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10 mm

Hot Crack


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Hot Cracking Causes:Hot Cracking Causes:

Imposition of excessive strains in restrainedImposition of excessive strains in restrained

weldswelds

Parent metal composition with excess sulphur,Parent metal composition with excess sulphur,PhosphorusPhosphorus

Base metal contaminationBase metal contamination

Inadequate filling of crater ( crater cracking)Inadequate filling of crater ( crater cracking)


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Hot Cracking Remedies:Hot Cracking Remedies:

Plan welding procedures which induce lessPlan welding procedures which induce less

thermal strainthermal strain

Use low sulphur, phosphorus containing baseUse low sulphur, phosphorus containing basemetal for weldingmetal for welding

Avoid contamination of base metalAvoid contamination of base metal


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COLD CRACKCOLD CRACK

Cold cracking is caused due to metal brittlenessCold cracking is caused due to metal brittleness

combined with a tensile stress exceeding thecombined with a tensile stress exceeding thefracture stress.fracture stress.

Brittleness is the result ofBrittleness is the result of

(a) Solidification of low melting constituents.(a) Solidification of low melting constituents.

(b) Phase changes (e.g. formation of martensite)(b) Phase changes (e.g. formation of martensite)during cooling.during cooling.


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Cold crack:Cold crack:

They are also called as UNDERBEAD CRACKThey are also called as UNDERBEAD CRACK

or DELAYED CRACK.or DELAYED CRACK.

Generally occurs in HAZGenerally occurs in HAZ They lie in directly adjacent to weld bead inThey lie in directly adjacent to weld bead in

HAZ area.HAZ area.

Subsurface and difficult to detect. HoweverSubsurface and difficult to detect. Howeverpropagate to surface and can be seen visually.propagate to surface and can be seen visually.


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Cold crackCold crack

Underbead crack occurs due to presence ofUnderbead crack occurs due to presence ofHydrogenHydrogen ininweld pool.weld pool.

Hydrogen comes from: Base metal,welding electrodes,Hydrogen comes from: Base metal,welding electrodes,organic surface contamination,surrounding atmosphereorganic surface contamination,surrounding atmosphere

This hydrogen may be absorbed by HAZ as H+ ions whenThis hydrogen may be absorbed by HAZ as H+ ions whenthe metal is in hot condition.the metal is in hot condition.

When solidified the metal has less capacity for theWhen solidified the metal has less capacity for thehydrogen and move though metal structure to grainhydrogen and move though metal structure to grain

boundary.boundary. At this instance individual H+ ions combines & form H2At this instance individual H+ ions combines & form H2

.This gases forms of hydrogen require more volume and.This gases forms of hydrogen require more volume andlarge enough to move though metal structure.large enough to move though metal structure.


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Factors promoting Cold crackFactors promoting Cold crack

Joint restraint and high thermal severity.Joint restraint and high thermal severity.

Hydrogen in the weld metal.Hydrogen in the weld metal.

Presence of impurities.Presence of impurities.

Embrittlement of HAZ in low alloy steels.Embrittlement of HAZ in low alloy steels.

Weld of insufficient sectional area.Weld of insufficient sectional area.

High welding speeds and low current density.High welding speeds and low current density.

Cold cracking occurs in both weld metal andCold cracking occurs in both weld metal andHAZ.HAZ.


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COLD CRAKING REMEDIES:COLD CRAKING REMEDIES:

Welding consumables must be hydrogenWelding consumables must be hydrogen

controlledcontrolled

Bake electrodes as recommended by electrodeBake electrodes as recommended by electrodemanufacturermanufacturer

Preheat as per Welding Procedure SpecificationPreheat as per Welding Procedure Specification

Heat input to be maintained even for tackHeat input to be maintained even for tackweldingwelding


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Lamellar TearingLamellar Tearing Fracture separation in heavy weldments, foundFracture separation in heavy weldments, found

within or just beneath HAZ of thick plates whichwithin or just beneath HAZ of thick plates whichwere not adequately refined by the steel mill.were not adequately refined by the steel mill.

Due to severe restraint on the joint.Due to severe restraint on the joint.

Poor ductilityPoor ductility

Presence of nonPresence of non--metallic inclusions running parallelmetallic inclusions running parallel

to the base metal surface.to the base metal surface.

Plate opens up as though it were made of stackedPlate opens up as though it were made of stackedsheets or lamellae so called Lamellar tearing.sheets or lamellae so called Lamellar tearing.

T and corner joints are more susceptible to lamellarT and corner joints are more susceptible to lamellar

tearing than others.tearing than others.


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Lamellar tearingLamellar tearing


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Radiograph showing CrackRadiograph showing Crack


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CRACKS SIGNIFICANCECRACKS SIGNIFICANCE

The most detrimental defect in weldingThe most detrimental defect in welding

They act as stress raisers for crack growth andThey act as stress raisers for crack growth and

not acceptablenot acceptable No fabrication code permits cracksNo fabrication code permits cracks


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Incomplete joint penetration:Incomplete joint penetration:

Penetration is the distance from the base metalPenetration is the distance from the base metal

top surface to the maximum extent of the weldtop surface to the maximum extent of the weldnugget.nugget.


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Incomplete penetrationIncomplete penetration


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Excessive PenetrationExcessive Penetration


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Causes of Incomplete jointCauses of Incomplete joint

penetration:penetration:

Improper Joints( U joint gives better than J buttImproper Joints( U joint gives better than J buttjoint)joint)

Too large root face.Too large root face.

Root gap too small.Root gap too small.

Less arc current.Less arc current.

Faster arc travel speed.Faster arc travel speed.

Too large electrode diameter.Too large electrode diameter. Misalignment.Misalignment.


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Radiograph:IncompleteRadiograph:Incomplete

penetrationpenetration


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Remedies of Incomplete Penetration:Remedies of Incomplete Penetration:

Use proper joint geometry.Use proper joint geometry.

Increase root opening or Use small electrode inIncrease root opening or Use small electrode in

root.root. Follow correct WPS (Welding ProcedureFollow correct WPS (Welding Procedure

Specification).Specification).


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Lack of fusionLack of fusion

Weld discontinuity in which fusion did notWeld discontinuity in which fusion did not

occur between weld metal and fusion facesoccur between weld metal and fusion facesjoining or adjoining weld beads.joining or adjoining weld beads.


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Lack of Fusion(LOF)Lack of Fusion(LOF)


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Factors promoting LOF:Factors promoting LOF:

Improper manipulation of welding electrode.Improper manipulation of welding electrode.

Weld joint design.Weld joint design.

Improper heat input.Improper heat input. Surface contamination which leads slagSurface contamination which leads slag

formation prevents fusion.formation prevents fusion.


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LOF REMEDIES:LOF REMEDIES:

Minimum heat input to be maintainedMinimum heat input to be maintained

Correct Electrode angleCorrect Electrode angle

Avoid molten pool flooding the arcAvoid molten pool flooding the arc Proper cleaning of oxides slagProper cleaning of oxides slag


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Radiograph:Lack of FusionRadiograph:Lack of Fusion


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INCLUSIONS:INCLUSIONS:

InclusionInclusion is entrapped foreign solidis entrapped foreign solid

material,such as slag,flux,tungsten or oxide.material,such as slag,flux,tungsten or oxide.

Associated with Lack of Fusion(LOF).Associated with Lack of Fusion(LOF).

Only occurs when any welding technique usesOnly occurs when any welding technique uses

Flux shielding.Flux shielding.

Due to Improper manipulation of weldingDue to Improper manipulation of welding

electrode and improper cleaning between multielectrode and improper cleaning between multirun .run .


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Radiograph:Slag InclusionRadiograph:Slag Inclusion


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INCLUSIONSINCLUSIONS

Tungsten inclusions are almost associated withTungsten inclusions are almost associated with

GTAW or TIG welding process.GTAW or TIG welding process.

Tungsten electrode makes the contact withTungsten electrode makes the contact with

molten weld puddle and remain in the final weldmolten weld puddle and remain in the final weldif not remove by grinding.if not remove by grinding.

Welding current is more than recommended.Welding current is more than recommended.


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REMEDIES FOR INCLUSIONREMEDIES FOR INCLUSION

Better interBetter inter--pass cleaningpass cleaning

Remove heavy convex beadsRemove heavy convex beads

Do not use electrodes with damaged coatingDo not use electrodes with damaged coating


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Radiograph:Tungsten inclusionRadiograph:Tungsten inclusion


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UNDERCUTUNDERCUT

Undercut is a surface discontinuity which occurs in the baseUndercut is a surface discontinuity which occurs in the basemetal directly adjacent to the weld.metal directly adjacent to the weld.

It is a condition in which the base metal has been melted awayIt is a condition in which the base metal has been melted away

during the welding operation and there was insufficient fillerduring the welding operation and there was insufficient fillermetal deposited to adequately fill the resulting depression.metal deposited to adequately fill the resulting depression.

This result is a linear groove in the base metal which may have aThis result is a linear groove in the base metal which may have arelatively sharp configuration.relatively sharp configuration.

Cause:Improper welding technique, Too high welding heatCause:Improper welding technique, Too high welding heat


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UndercutUndercut


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Radiograph: UNDERCUTRadiograph: UNDERCUT


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Radiograph: UNDERCUTRadiograph: UNDERCUT


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UnderfillUnderfill

UnderfillUnderfill A condition in which the weld face or rootA condition in which the weld face or rootsurface extends below the adjacent surface of the basesurface extends below the adjacent surface of the basemetal.metal.

Underfill at the root weld of Pipes are termed asUnderfill at the root weld of Pipes are termed as INTERNALINTERNAL

CONCAVITY or SUCK BACKCONCAVITY or SUCK BACK It can be cause by excessive heating and melting of root passIt can be cause by excessive heating and melting of root pass

during deposition of second pass.during deposition of second pass. Cause: Excessive travel speedCause: Excessive travel speed


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UnderfillUnderfill


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Radiograph:Internal concavityRadiograph:Internal concavity


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OverlapOverlap

Overlap is described as the protrusions of weld metal beyond theOverlap is described as the protrusions of weld metal beyond the

weld toe or weld root.weld toe or weld root. Also called as rolloverAlso called as rollover

Cause:Improper welding technique like slow arc travel speed.Cause:Improper welding technique like slow arc travel speed.


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OverlapOverlap


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MisalignmentMisalignment

Offset or mismatch occurs where two piecesOffset or mismatch occurs where two pieces

welded together are not properly aligned.welded together are not properly aligned.


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Inadequate weld reinforcementInadequate weld reinforcement


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Excessive weld reinforcementExcessive weld reinforcement


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SpatterSpatter

AWS A 3.0 describes spatter as metal particlesAWS A 3.0 describes spatter as metal particles

expelled during fusion welding that do not formexpelled during fusion welding that do not forma part of weld.a part of weld.

Cause: High welding current which can causeCause: High welding current which can causeexcessive turbulence in the weld zone.excessive turbulence in the weld zone.

Its presence gives difficulty in UT,MT,PTIts presence gives difficulty in UT,MT,PT

Premature failure of applied coatings.Premature failure of applied coatings.


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SpatterSpatter


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Arc StrikesArc Strikes

Arc strikes result when the arc is initiated on theArc strikes result when the arc is initiated on the

base metal surface away from the weldbase metal surface away from the weldjoint,there is a localized area of the base metaljoint,there is a localized area of the base metal

surface which melts and rapidly cooled.surface which melts and rapidly cooled.

In high alloy steel it can create localized HAZIn high alloy steel it can create localized HAZ

which leads to crack initiation.which leads to crack initiation.

Cause: Improper welding techniqueCause: Improper welding technique

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