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06.2003Welding ofSteel Pressure Vessels Orig.:Checked:Appr.:Total6Pages Descriptors:PressureVessel,Welding,Steel ReplacesIssue
2.1Quality ManagementSystem Thecontractor shall have anappropriate qualitymanagement system,e.g.:•in accordance with ISO9001,9002,9003or•compliance with the requirementsof EN729-2as aminimum or•manufacturer isASME U-Stamp holderLINDE reserves the right to auditthe implementationof thequality requirements.Page2Issue
06.
20032.2Subcontracting Thesubcontracting of welding andheat treatmentwork and nondestructive testing of welds shall bepermitted with the writtenapproval of the Purchaseronly.The manufacturer shall ensurethat hissubcontractors arefully informedof Purchasersrequirements;he shallconvince himselfof thecompliance with these requirements,including theobservance of the requirementsof thepresent standard.
2.3Welders andWelding ProceduresThe weldersand welding procedures to be employedfor thework shall be qualifiedin accordance with the specified code.This appliesalso torepair welds.The Purchaserreservestherighttoreview therelevant qualifications.
2.4Filler Materialsand AuxiliaryMaterials
2.
4.1For theirintended scopeof applicationthe filler materials shall be qualification-tested and/or approvedby the manufacturer offiller materialsacc.to thespecified code,i.e.in generalbase metal matching fillerswith referenceto strength,toughness and corrosion resistance,unless base metal deviatingproperties Re,Rp,creep rupturestrength have been consideredfor vesseldesign/calculation.
2.
4.2For dissimilarjoints,i.e.welds betweendifferent steelgrades,the filler material shall be suitedfor anyintended heat treatment andfor theoperating temperatureand operatingfluid.
2.
4.3Filler materials and auxiliarymaterialsand welding flux shall bestored insuch away thatthey cannot be confused,and shall be treatedproperly accordingto the manufacturers recommendations,e.g.drying ofcoated electrodesandweldingflux beforeuse.
2.5Manufacturing FacilitiesThe manufacturer shallhavesuitable facilitiesfor forminge.g.rolling of the shellcourses,weld bevel preparation,preheating,welding and-where required-heat treatment.Heat treatmentfacilities shall be inspectedfor proper function and accuracy at regular intervals.
2.6Testing FacilitiesandTestPersonnel Themanufacturershallhave qualifiedtest andsupervisory personnel,suitable testingequipment and facilities as well asworking instructionsfor theintended testing.The equipmentandfacilitiesshall bechecked forproperfunctionandaccuracyatregularintervals.
2.7Marking SystemsProcedures shall be implementedin themanufacturers works,which ensurean unambiguouscorrelation:•of componentsto the material certificates;•of welds to thewelder;•of testedweldsto the reportof nondestructive tests andto eachindividual film;•ofpressure vessels tomanufacturing documentsand acceptancedocumentation.3Design andForm
3.1General Themanufacturershallestablish thetechnical documentsrequired forthe propermanufacture and testingof a pressure vessel,by observingthespecifiedrequirements.Site weldsshall beclearly indicatedin thesedocuments.A testassembly in themanufacturersworks shallgenerally beconsidered andit shall be indicated,when the pressurevesselwill becompleted onsite.The purchaseorder specifieswhich manufacturingdocuments shall be submittedto thePurchaser orthird partiesfor reviewprior tostart ofmanufacturing.
3.2Welds inPressure-Bearing Walls
3.
2.1Butt weldsshall be welded withfull penetration.Seams accessiblefrom bothsides shall be welded from bothsides.For single-side welds,the welding procedure shall be soselected thatan integerroot weldis achieved.Permanent backingstrips shall be approvedby Linde.For both-sides weldedseams back-gouged rootshall bechecked for freedom ofdefects.
3.
2.2An accumulationof weldsshall be avoided;therefore,the followingshallapply:•Cross jointsare notpermitted;•Distance ofnozzle weldsto circumferentialor longitudinalwelds:3x ss=shell wall thickness,but notless than50mm;If theabove specifiedrequirements cannot be observedinaspecific case,a100%nondestructive volume test shall be performed.•Distance betweenparallel buttwelds:6xs,but notless than50mm.
3.
2.3Pressure-bearing weldsshould notbe coveredby attachmentse.g.saddles,reinforcement pads.If thisis unavoidable,the weldswhich willlater becovered shallfirst beground flushwith thebase metaland thefreedom ofdefects shall be verifiedby avolumetestradiographic/ultrasonic test.
3.3Attachments
3.
3.1Attachments cominginto contactwiththefluid inpressure vesselsin corrosiveservice withcorrosion allowances1mm andvessels ofstainless steelshall be welded with a continuous fillet weld.A ventingof hollow spaces shall be providedfor onthe lowestpoint of the filletweld bya shortweld interruption.Tray ringsin columnsshall beseal-welded with a continuousweld ontheir upperside;the lowerside canbeweldedwith staggering.
3.
3.2External attachmentscoming notinto contactwiththefluid shall beweldedwith acontinuousfilletweld,irrespective of their stresses,so thatrain and/or condensationwater cannotpenetrate into the gapsand leadto corrosionof thevessel wall.A ventingof hollowspaces shall be providedfor onthe lowestpoint of the filletweld bya shortweld interruption.
3.
3.3Welds inreinforcing padsof nozzlessegment welds in openingreinforcements shallnotbearranged parallelto thelongitudinal axisofthevessel.These seamsshall bewelded separatelyfrom thevessel.
3.
3.4Venting ofhollowspacesshall be performed for attachments such as saddles,block flanges,reinforcing padswithaventing bore###6mm,reinforcing padswithatapped boreper segmentfor inspectionpurposes.4Manufacturing andTesting
4.1General Manufacturingmay bestarted onlythen,when the manufacturing requirementsacc.to section2havebeenfulfilled.The documentsreviewed inaccordancewithsection
3.1shall bebinding forthe manufacturingandtestingofapressurevessel.Deviations fromthese needthe writtenapproval ofthe authorityies.In additiontothefollowing generalrequirements,the material-specific requirements as persection6shall beobserved.Page4Issue
06.
20034.2Weld BevelPreparation
4.
2.1For fine-grained steels with Re355N/mm2,high-temperature CrMo-steels andaustenitic steels,thermal cutbevels shallbe machinede.g.by grindingand testedfor freedom of scaleand cracks.
4.
2.2If thebevels arenot machined,the plasmaprocess onlyis permitted for weldbevelpreparationof austenitic steels
4.
2.3Paint coatsand othercoatings shallbe removedcompletely inan area25mm tothe weldingbevel.
4.3Preheating Inaccordancewiththe welding procedure specification,dependent onmaterial,wall thicknessand ambienttemperature.At temperatures5℃or risk of formation of condensationthe partstobewelded shallgenerally bepreheated.
4.4Tack WeldsTack welds are subject tothe same requirementspreheating,welding data,weldingprocedure qualification,welder qualificationas theweldsincomponents.Components intack-welded stateare subject to avisual inspectionmisalignment ofthe edges,axes misalignment,angularity,freedomof cracks ofthe tacks,cleanliness.
4.5Temporary AttachmentWelds Temporarywelded attachment weldsshallbe base metalmatchingand shallbeperformedwith appropriatefiller materialsacc.to section
2.4and aresubjecttothesamerequirementsascomponent welds.They shallbe removedprofessionally withoutdamage tothe pressure-bearing wall.A knockingoff ofthe temporaryattachmentweldsis notpermitted.Any seamresidues remainingshallbeground flushwiththebase metal;these locationsshallbesubjecttoa finalsurface crack inspection.
4.6Weld RepairsDefective areasshallberemoved usingprocesses suitedtothematerial.Before repairwelds arecarried out,a surfacecrackinspectionshallbemade.Repair weldsand subsequentnondestructive testingshallbecarried outby qualifiedpersonnel usingsuitable processesand shallbe recordedin thevessel documentation.
4.7Weld-and ComponentSurfaces Spattersand arc strikes shallbeavoided.Spatters occurrednevertheless andarcstrikesshallbeground.Arc strikesshall thenbe testedforfreedomofcracks.The seamcontour shallbe insuchaway thata softseam transitionis given.If necessary,seam transitionsshallbeground correspondingly.
4.8Production WeldTest Plates
4.
8.1For pressure vessels subjectto postweldheat treatment and withimpact requirementsthe production weld test plates shallbe divided;one half shallbesimulating heattreated immediatelyand then tested.If therequirements are met,the secondhalfshallbe heattreated withthepressurevessel and thentested.
4.
8.2If forpressurevesselswith siteassembly seams,object-related productionweld testplates arerequired,themanufacturerofthevessel hasto deliverthe platematerial therefore.
4.9Time ofTest Specifiednondestructivetestsand hardnesstests onthe componentshallbecarried outafter formingand/or heat treatment,i.e.in thefinal state.The resultsshallberecorded foreach seam.5Postweld HeatTreatment
5.1Heat treatmentsshallbequalified withthe weldingprocedure qualificationand shallbe definedin the weldingprocedurespecification WPSaswellas inthemanufacturingdocuments.If repairwelds necessitatea newheat treatment,the weldingprocedurequalificationshallbequalified withthe accumulatedheat treatmenttime.Pressure vesselsmade ofquenched andtempered steelse.g.CrMo-and Ni-steels shallbe stress-relieved at20to30℃below thetempering temperatureofthebase metal.
5.2Welding workon pressure-bearing componentsis notpermitted afterheattreatmenthas beencompleted.
6.Material-specific Requirements
6.1C-and C-Mn-Steels
6.
1.1At ahigh carboncontent C
0.25%or highcarbon equivalentC+Mn/
60.4there isa riskof cracking intheheat affectedzone becauseofthehigh levelof hardness.Depending onthematerialanalysis,wallthickness,weldingprocedureand ambienttemperature,sufficient preheatingis required.
6.
1.2For elevatedstrength fine-grained steelswith Re355N/mm2,the riskof hydrogen-induced coldcracks shallbe reducedby preheating,limited controlled heat inputand-for wallthicknesses30mm only-hydrogen effusiontreatment soakingat280℃-300°C for2to4hours.Fillet weldsshallbewelded inat leasttwo passes,seam lengthforattachmentsat least50mm;nondestructive testingofthewelds notearlier than48hours afterwelding,if theweldsarenot subjectto postweldheattreatment.
6.2High-Temperature Cr-Mo-Steels Hardnessof weld deposit andheat affectedzone shallnotbemore than100units abovethe hardnessofthebasemetal,but nothigher than350HV
10.Verification onthe componentrandom samplesand onproductionweld testplates,if requiredby code.
6.3Ni-Steels forLow TemperatureService
6.
3.1Filler materialsaustenitic orNi-based dissimilarto basemetal arepermittedforsteelswith Ni###5%only.For dissimilarfillermaterialit shallbe verifiedby weldingprocedure qualificationsand productionweldtestplates thatthe mechanical properties yieldstrength,tensile strengthused forthe dimensioningaremetinthewelddeposit.
6.
3.2For steelswithNi###5%:Remanent magnetismcan deflectthe arcand thuscause lackof fusion.Preventive measuresare:•no useof magneticcranes,no transportationby trainwith electricoverhead linesandnomagnetic particletest;•avoidance ofaccidential magnetizationby electricconductors such as cablesor electricalequipment;•nondestructive testingof allpressure-bearing welds100%for lackof sidefusion.
6.4Austenitic CrNi-Steels
6.
4.1Grinding discsspecially suitablefor CrNi steel andbrushes ofCrNisteelshallbeused forCrNi-steels only.Machining ofausteniticsteelsspatially separatedfrom ferriticsteels ornonferrous metals.
6.
4.2For single-side welding,root protectionargon or purging gasis required.
6.
4.3Interpass temperature###200℃,avoidance ofoverheating.
6.
4.4Delivery conditionmetallic bright,i.e.without scaleand annealingcolours,free fromoil andgrease.Page6Issue
06.
20036.5Duplex SteelsAs toferritic-austenitic duplexsteels,mechanicalpropertiessuchashardness,impact toughnessandcorrosionresistance areparticularly influencedby thewelding technique.Therefore,theweldingof duplexsteels requiresspecific experience.The followingrequirements shallalways beobserved:•Processing similarto austeniticCrNi steels;•Filler materialwith higherNi-content comparedtothebasemetal;•Arc strikesoutside theseam andfusion withoutfillermaterialshallbeavoided;•Relatively highshrinkage stressesshallbetaken intoconsideration=riskofcrackinginthin cross-sections;•Welding withlimited andcontrolledheatinput,avoidance ofoverheating,particularly forroot passesand thincross-sections;•Root protectionfor seamsweldedfromone sidewith Ar
99.996%,nitrogen
99.996%orpurginggas90%N2+10%H2,•Removal ofslag residuesand annealingcolours afterwelding bymeans ofbrushing,blasting orpickling;•Postweld heattreatmentandrepeated heatingofweldrepairs canbe criticaldue tochanges inthe ferrite/austenite distributionandtheformationofprecipitations.。