Welding- properties of fusion welding

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PropertiesoffusionweldsVIJAYANMG

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WeldingvcastingWeldmustadheretomouldwall Heatisaddedcontinuallytoweldsq

Weldssolidifymuchfasterthancastings Inwelds,thesurfaceshapeisconstant Thereisstrongmixingofweldpools

Hightemperaturegradient

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FusionweldstructureFusionline Weldpreparation Base metal Weldmetal

HAZ

HAZ

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ThermalgradientsinHAZTemperature Fusionline Fusionline+2mm Fusionline+5mm

Time Qualmet Services4

HAZstructureHighpeaktemperature Hightemperaturegradientq

SuperimposedHAZsinmultipasswelds Weldingstressesaffecttransformation

Variablecoolingrate

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Multipassfusionweld

Lastweldrun Previousweldrun

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WeldpropertiesWeldmetalhasdifferentcomposition& thermalhistorytobasemetal Weldingheatmodifiesadjacentbasemetal (HAZ) Variationinstrength,ductility&corrosion resistanceacrosswelds

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WeldingprocedureSelectionofprocessconditions& consumablesforaweld Designedtomatchbasematerialproperties ascloselyaspossible&avoidwelddefects Needstoconsiderserviceconditionsofthe weld

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DefinitionofweldabilityThecapacityofamaterialtobewelded undertheimposedfabricationconditions intoaspecific,suitablydesignedstructure& toperformsatisfactorilyinintendedservice. (ANSI/AWSA3.0)

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FactorsaffectingweldabilityWeldabilityisoftenconsideredtobea materialproperty,howevertheeffectofother variablesshouldnotbeignored. Designofweldment Itsserviceconditions Choiceofweldingprocess

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MaterialpropertiesMelting&vaporisationtemperatures Electrical&thermalpropertiesq

AffinityofweldmetalforO,N&Hq

Conductivity,expansioncoefficient,thermal capacity,latentheat Susceptibilitytoporosity,embrittlementorwetting problems Oxide,paintormetallicsurfacecoating

Presenceofasurfacefilmonbasemetalq

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ServiceenvironmentExtremeenvironmentsq q q q

Themoreextremetheenvironmentq q

Corrosive Lowtemperature(brittlefailure) Hightemperature(oxidation,creep,embrittlement) Others(wear,fatigue,nuclear) Themoredifficultitistofindsuitablematerials Themorerestrictedtheweldingprocedurebecomesto avoidservicefailure

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WeldingDefectsCracksq

Porosityq

InweldmetalorHAZ Gasbubblesentrappedinweldmetal

Incompletefusion(interrunoratpreparationedge) Inclusionsq

Defectiveprofileq

Slagorothermatterentrappedinweld

Underweld,overweld,lackofpenetration,overlap, undercut13

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CausesofwelddefectsPoordesignofweldmentq

Mistakesbywelderq q q

Lackofaccesstomakeweld Lackofskill Poorplacementofweldmetal Inadequatecleaning

Poorweldingprocedure

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Welddefects

Slag inclusion

Wormhole porosity Incomplete fusion

Overlap

SolidificationcrackingContractionstrains causeruptureofthe weldatthepointwhere thelastmaterial solidifies.q q

Solidificationrange Weldpoolsize&shape

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Residualstress&distortionUnevenheatingleadstoconstrainedthermal expansion Atcompletionoftheweldthermalcyclethe weldmenteitherdistortsorifrestrainedwill containresidualstress Residualstressfieldsarecomplex,but stressesashighasyieldoftenoccur Stressesmayneedtoberemovedbyastress reliefheattreatmentQualmet Services17

Residualstressinabuttweldy s X x s XCompression y 0

x sTension

Tension

X

XCompression

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Welddetailing

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Weldpositionsplate

Flat (1G)

Horizontal (2G)

Vertical (3G) UporDown

Overhead (4G)20

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Weldingpositionspipe

Axisvertical 2G

Axishorizontal 5G

Axisinclined45 6G

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WelddetailsJointsArrangementsofmembersbeing joinedq

WeldsGeometryofwelddetailselectedto makethejointq

Butt,tee,lap,corner,flare

Butt,fillet,plug&slot

Jointtypes

Butt

Tee

Edge Lap Corner23

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WeldtypesButtweldq q q

Filletweldq q

Betweenmatingmembers Bestquality Highweldpreparationcost Easypreparation Asymmetricloads,lowerdesignloads Modifiedfilletweldsinlapjoints,using holesthroughonemember24

Plug&slotweldsq

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FilletweldsSimple&cheaptoassemble&weld Stressconcentrationsattoes&root Notchatroot(fatigue,toughness) Criticaldimensionisthroatthickness Rootgapaffectsthroatthickness Radiography&ultrasonictestingisof limiteduse Largefilletsusealotofweldmetal& thereforeareuneconomic

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FilletweldtermsToe Weldface

Root

Toe Gap

Throat thickness

Apparentleglength

ButtweldsTypes:q q q

Lowerstressconcentration Easierultrasonictestingorradiography ExpensivepreparationQualmet Services

Doubleweldedbutt Permanentortemporarybacking Singleweldedbutt

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Buttweldtypes

Singlevee canbesingle ordoublewelded

Singlebevel

Doublevee

Backedbutt(permanentortemporary)

ButtweldtermsFusionface Includedangle Bevelangle

Reinforcement Rootface Root gap Toe Toe

Rootrun

WeldpreparationdimensionsCompromiseq

Weldcrosssectionalarea

Standardpreparationsq

Cost Easeofwelding(riskofdefects)

Fabricatorsrisk

AS1554,AWSD1.1,ANSIB31.3

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SingleweldedbuttjointsAccesstoonesideonlyq

Rootrunformsinsidesurface Highfituptolerancesrequired Highskillrequiredq

Pipe&hollowsectionbuttjoints

Rootmaybecontaminated Insideisdifficulttoinspect

Specialwelderqualification

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J&UPreparationsUpreparation

Rootradius Land

DoubleUbutt Qualmet Services32

AS1101.2drawingsymbolsOTHERSIDE Tail ARROWSIDE Referenceline Arrowpointstoweld location

Weldtypesymbol

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TypicalAS1101.2symbols6 6mm CJP

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