Welding,CuttingandBrazingIntroductionWelding,cutting,andbrazingareexceptionallydangerous.Compressedgasesareoftenusedtocreateanextremelyhotflame.Differentweldingtechniquescancauseotherhazards.Theweldercanbeinjuredorcausedamagetotheworkareainnumerouswaysincludingfire,explosion,gas,andfumehazards.Goodworkpracticesmustbefollowedinallwelding,cutting,andbrazingtechniquestopreventinjuries,fires,andexplosions.Thismodulecoversthefollowingsections:lCompressedGaseslGeneralRequirementslOxygen-FuelGasWeldingandCuttinglArcWeldingandCuttinglResistanceWelding.Introduction-ObjectivesAttheendofthisWelding,Cutting,andBrazingmodule,youshouldbeableto:lUnderstandthegeneralrequirementsconcerningcompressedgaseslIdentifythegeneralsafetyrequirementsforalltypesofweldinglUnderstandthegeneralcharacteristicsforthevarioustypesofweldinglIdentifythespecificsafetyrequirementsfor:lOxygen-fuelgasweldingandcuttinglArcweldingandcuttinglResistancewelding.CompressedGases-IntroductionManyweldingandcuttingoperationsrequiretheuseofcompressedgases.Tounderstandthesehazards,wemustunderstandthatcompressedgasesarestoresofpotentialenergy.Ittakesenergytocompressandconfinethegas.Thatenergyisstoreduntilpurposelyreleasedtoperformusefulworkoruntilaccidentallyreleasedbycontainerfailureorothercauses.Somecompressedgases,acetyleneforexample,havehighflammabilitycharacteristics.Flammablecompressedgases,therefore,haveadditionalstoredenergybesidessimplecompression-releaseenergy.Othercompressedgases,suchasnitrogen,havesimpleasphyxiatingproperties.Somecompressedgases,suchasoxygen,canaugmentorcompoundfirehazards.CompressedGases-IntroductionCompressedgasesareregulatedbymanystandards.Twoprimarystandardsare:l29CFR1910SubpartQWelding,Cutting,andBrazingcoversthehandling,storage,anduseofcompressedgases,suchasoxygen-fuelgas,whentheyareconsumedintheweldingprocess.l29CFR1910SubpartHHazardousMaterials,1910.101-1910.105coversthegeneralrequirementsforthehandling,storage,anduseofcompressedgasesotherthanthoseconsumedintheweldingprocess.TheGeneralRequirementssectionof1910.101isconcernedwith:lCylinderinspectiontoincluderequiredmarkingslHandling,storage,andutilizationlInstallationandmaintenanceofsafetyreliefdevicesCompressedGasesGeneralRequirementsInadditiontotheOccupationalSafetyandHealthAdministration(OSHA)regulationsfoundinSubpartsQandHof29CFR1910thereareotherapplicableregulationsandinformation.TheseincludetheDepartmentofTransportation(DOT)regulations,andtheCompressedGasAssociation(CGA)pamphlets.Thesesourcesprovidetherequirementsforthegeneralcategoryofcompressedgasesandcertainspecificcompressedgases.Animportantaspectoftheseregulationsisthesafetyofcompressedgasstoragecontainers.Specificrequirementsaremadeofemployersfortheinspectionofthecompressedgascylinders.Visualinspectionsarerequiredtoensurethatthecylindersaresafe.Thenextpagewillgointomoredetailregardingvisualexaminationsofcompressedgasstoragecontainersandthesafetyofthesecontainers.CompressedGasesGeneralRequirementsEmployeesshalldeterminethatcompressedgascylindersundertheircontrolareinasafeconditiontotheextentthatthiscanbedeterminedbyvisualinspection.Visualandotherinspectionsarerequired,butotherinspectionsarenotdefined.TheseinspectionsmustbeconductedasprescribedintheHazardousMaterialsRegulationsoftheDOTcontainedin49CFRParts171-179and14CFRPart103.Wheretheseregulationsarenotapplicable,theseinspectionsshallbeconductedinaccordancewithCGAPamphletsC-6andC-8.AccordingtoDOTregulations:Acylinderthatleaks,isbulged,hasdefectivevalvesorsafetydevices,bearsevidenceofphysicalabuse,fireorheatdamage,ordetrimentalrustingorcorrosion,mustnotbeusedunlessitisproperlyrepairedandrequalifiedasprescribedintheseregulations.Thetermcylinderisdefinedasapressurevesseldesignedforpressureshigherthan40psia(poundspersquareinchabsolute)andhavingacircularcrosssection.Itdoesnotincludeaportabletank,multi-unittankcartank,cargotank,ortankcar.DOTMarkingRequirementsEachDOTmarkingidentifiedonthispagemustappearonallcylindersandmustbemaintainedsothatitislegible.Thecirclednumbersonthegraphiccorrespondtothenumbereddefinitionsprovidedbelow.1.ICCorDOTmarkingmayappear:ICC:Pre-existingmarkingICC3AA20153AA-specificationfrom49CFR178.372015-markedservicepressure.DOT:newmanufacturemarkingmustreadDOT.49CFR171.14.2.A35798641:Serialnumber-noduplicationspermittedwithanyparticularsymbol-serialnumbercombinations.3.PST:Symbolofmanufacturer,user,orpurchaser.4.656:dateofmanufacture.Monthandyear.:disinterestedinspectorsofficialmark.5.+:indicatescylindermaybe10%overchargedper49CFR173.302(c).6.5-61and5-66:Retestdates.7.*(5pointedstar0:indicatestenyearretestinterval.See49CFR173.34(e)(15).CompressedGasesGeneralRequirementsInadditiontotheguidanceintheOSHAregulations,CompressedGasAssociation(CGA)pamphletsdeterminerequirementsforhandling,storing,andusingcompressedgasesincylinders,portabletanks,railtankcars,andmotorvehiclecargotanks.Theyalsoidentifyhowtoinstallandmaintainrequiredpressurereliefvalvesonthesecontainers.Thein-planthandling,storage,andutilizationofallcompressedgasesincylinders,portabletanks,railtankcars,andmotorvehiclecargotanksshallbeinaccordancewithCGAPamphletP-1.Compressedgascylinders,portabletanks,andcargotanksshallhavepressurereliefdevicesinstalledandmaintainedinaccordancewithCGAPamphletsS-1.1andS-1.2.CompressedGasesSpecificGasesTheOSHAregulationscontainsomesectionsregulatingspecificcompressedgases,including:lAcetylenelHydrogenlOxygenlNitrousoxidelAnhydrousammonialLiquefiedpetroleumgases.OthercompressedgasesareincommonuseandfallunderregulationSubpartH,1910.101.Examplesincludechlorine,vinylchloride,sulfurdioxide,methylchloride,hydrogensulfide,ethane,compressedair,andnitrogen.GeneralRequirements-IntroductionTheGeneralRequirementssection,1910.252providesinformationaboutprotectingindividualsduringwelding,cutting,orbrazingoperations.Thissectioncontainsthethreetopicslistedontheleft.Protectionoftheindividualincludesmeasurestakento:lPreventfiresfromoccurringlEliminatefiresiftheyoccurlProtectpersonnelbyprovidingappropriateclothingandequipmentlProtectpersonnelwhenweldingorcuttingcontainerslProtectpersonnelworkinginconfinedspaces.GeneralRequirementsFirePreventionandProtectionFirepreventionandprotectionincludebasicprecautions,specialprecautions,andsafetyprecautionsfortheuniquesituationsinvolvingweldingandcuttingcontainers,andweldinginconfinedspaces.Thebasicprecautionsforfirepreventioninwelding,cutting,andbrazingfocusonremovaloffirehazards.Theyincludethefollowing:lIftheobjecttobeweldedorcutcannotreadilybemoved,allmovablefirehazardsinthevicinityshallbetakentoasafeplacelIftheobjecttobeweldedorcutcannotbemovedandifallthefirehazardscannotberemoved,thenguardsshallbeusedtoconfinetheheat,sparks,andslag,andtoprotecttheimmovablefirehazardslIftheaboverequirementscannotbemet,thenweldingandcuttingshallnotbeperformed.GeneralRequirementsFirePreventionandProtectionComplyingwiththebasicprecautionsforpreventionoffiresinweldingisnotenough.Specialprecautionsmustalsobetaken.Theseincludehavingtheproperfireextinguishingequipmentavailableandhavingfirewatcherspresent,ifneeded.Suitablefireextinguishingequipmentshallbemaintainedinastateofreadinessforinstantuse.Suchequipmentmayconsistofpailsofwater,bucketsofsand,hoses,orportableextinguishersdependinguponthenatureandquantityofthecombustiblematerialexposed.Firewatchersarerequiredwheneverweldingorcuttingisperformedinlocationswheremorethanaminorfiremightdevelop,orwhereanyofthefollowingconditionsexist:lAppreciablecombustiblematerials,inbuildingconstructionorcontents,closerthan35feettothepointofoperationlAppreciablecombustiblematerialsmorethan35feetaway,butareeasilyignitedbysparks.Afirewatchshallbemaintainedforatleastahalfhouraftercompletionofweldingorcuttingoperationstodetectandextinguishpossiblesmolderingfires.GeneralRequirementsFirePreventionandProtectionEvenifallofthespecialprecautionshavebeentaken,therearestillcertainsituationsinwhichwelding,cutting,orbrazingarenotallowed.Cuttingorweldingshallnotbepermittedin:lAreasnotauthorizedbymanagementlBuildingswithimpairedsprinklersystemslThepresenceofexplosiveatmospheres(mixturesofflammablegases,vapors,liquids,ordustswithair)lLocationswhereexplosiveatmospheresmaydevelop,suchas:lInsideuncleanorimproperlypreparedtanksorequipmentwhichhavepreviouslycontainedsuchmaterials(flammablegasses,vapors,liquids,ordusts)lAreaswithanaccumulationofcombustibledusts.GeneralRequirementsFirePreventionandProtectionWeldingandcuttingcertaincontainersmayconstituteaspecialsituationthatrequiresadditionalsafetyprecautionsbeyondbasicandspecialprecautions.Nowelding,cutting,orotherhotworkshallbeperformedonuseddrums,barrels,tanks,orothercontainersuntiltheyhavebeenthoroughlycleaned.Cleaningmustremoveallflammablematerialspresentoranysubstancessuchasgreases,tars,acids,orothermaterialswhichmightproduceflammableortoxicvaporswhensubjectedtoheat.Anypipelineorconnectionstothedrumorvesselbeingweldedshallbedisconnectedorblanked.GeneralRequirementsFirePreventionandProtectionWorkinginconfinedspacesinvolvesadditionalsafetyprecautionsbeyondthebasicandspecialprecautions.Aconfinedspaceisdefinedin29CFR1910.252asarelativelysmallorrestrictedspacesuchasatank,boiler,pressurevessel,orsmallcompartmentofaship.Adequateventilationisaprerequisitetoworkinconfinedspaces.Whenweldingorcuttingisbeingperformedinanyconfinedspace,thegascylindersandweldingmachinesshallbeleftontheoutside.Whenarcweldingistobesuspendedforanysubstantialperiodoftime,suchasduringlunchorovernight,allelectrodesshallberemovedfromtheholders.Theholdersshallbecarefullylocatedsothataccidentalcontactcannotoccurandthemachineshallbedisconnectedfromthepowersource.GeneralRequirementsFirePreventionandProtectionWhensuspendinggasweldingorcuttingoperations,eliminatethepossibilityofgasescapingthroughthenozzlebyclosingthetorchvalves.Thegassupplytothetorchmustbepositivelyshutoffatsomepointoutsidetheconfinedareawheneverthetorchisnottobeusedforasubstantialperiodoftime,suchasduringlunchhourorovernight.Wherepracticable,thetorchandhoseshallalsoberemovedfromtheconfinedspace.Whereweldersmustenteraconfinedspacethroughamanholeorothersmallopening,meansshallbeprovidedforquicklyremovingthemincaseofemergency.Anattendantwithapre-plannedrescueprocedureshallbestationedoutsidetoobservethewelderatalltimesandshallbecapableofputtingrescueoperationsintoeffect.GeneralRequirementsProtectionofPersonnelProtectionofpersonnelfocusesonprotectingthewelderfromhazardsotherthangeneralfireprotection.Protectionofpersonnelinweldingorcuttingoperationscaninvolvefallprotection,eyeprotection,andprotectiveclothing.Whenworkingatheights,awelderorhelperworkingonplatforms,scaffolds,orrunwaysshallbeprotectedagainstfallingthroughtheuseof:lRailingslSafetybeltslLifelineslSomeequallyeffectivesafeguards.GeneralRequirementsProtectionofPersonnelWelding,cutting,orbrazingoperationsconductedwithoutpropereyeprotectioncreateaseriouseyeinjuryhazard.Helmetsandhandshieldsshallbearrangedtoprotecttheface,neck,andearsfromdirectradiantenergyfromthearc.Theyshallbeusedduringallarcweldingorarccuttingoperations,excludingsubmergedarcwelding.helpersorattendantsshallbeprovidedwithpropereyeprotection.Helmetsandhandshieldsshallbemadeofamaterialwhichisaninsulatorforheatandelectricity.Helmets,shields,andgogglesshallnotbereadilyflammableandshallbecapableofwithstandingsterilization.Wheretheworkpermits,theweldershouldbeenclosedinanindividualboothorinanon-combustiblescreenpaintedwithafinishoflowreflectivitysuchaszincoxide(animportantfactorforabsorbingultra-violetradiation)andlampblack.Boothsandscreensshallpermitcirculationofairatfloorlevel.Peopleadjacenttotheweldingareasshallbeprotectedfromtheraysbynon-combustibleorflameproofscreensorshieldsorshallberequiredtowearappropriategoggles.GeneralRequirementsProtectionofPersonnelBecauseofthedangerofburnsandclothingcatchingfire,employeesexposedtothehazardscreatedbywelding,cutting,orbrazingoperationsshallbeprotectedbypersonalprotectiveequipmentinaccordancewiththerequirementsof29CFR1910.132.Appropriateprotectiveclothingrequiredforanyweldingoperationwillvarywiththesize,nature,andlocationoftheworktobeperformed.Weldersshouldalwaysselectclothingmaterialswhichwillprovidemaximumprotectionfromsparksandhotmetal.Theshirtshouldhavefullsleeves,nopockets,andshouldbewornoutsidethetrouserswithcollarbuttoned.Thetrousersshouldhavenocuffsandshouldextendwelldowntothesafetyshoes.Safetyshoesandfire-resistantgauntletglovesarealsoneeded.GeneralRequirementsHealthProtectionsandVentilationRegardlessoftheprecautionarymeasurestaken,somematerialsrequirespecialventilationbecausetheyareparticularlyhazardous.Mechanicalventilationandotherspecificcontrolmeasuresarerequiredwhenweldingorcuttingisdonewiththefollowingmaterials:lFluorinecompoundslZinclLeadlBerylliumlCadmiumlMercurylCleaningcompoundslStainlesssteelOxygen-FuelGasWeldingandCutting-IntroductionInthisWelding,Cutting,andBrazingmodule,threespecifictypesofweldingarecovered.Thesearelistedbelow:lOxygen-fuelgasweldingandcuttinglArcweldingandcuttinglResistancewelding.Thissectiondealsspecificallywithoxygen-fuelgasweldingandcutting.TheOxygen-FuelGasWeldingandCuttingsectionisbasedon29CFR1910.253.Thissectionprovidesinformationaboutthefivetopicareasthatarelistedtotheleft.Eachtopicispresentedwithguidanceinformationsothatyouwillbeabletopreventaccidentsandpromoteworksafetywhenweldingorcutting.Oxygen-FuelGasWeldingandCutting-IntroductionGeneralRequirementsofOxygen-FuelGasWeldingandCutting,29CFR1910.253,focusesonusingacetylenesafely.Undernoconditionsshallacetylenebegenerated,piped(exceptinapprovedcylindermanifolds),orutilizedatapressureinexcessof15poundspersquareinchgauge(psig)or30poundspersquareinchabsolute(psia).The30psialimitisintendedtopreventunsafeuseofacetyleneinpressurizedchamberssuchascaissons,undergroundexcavations,ortunnelconstruction.Absolutepressureisequaltogaugepressureplusatmosphericpressure,whichatsealevelaverages14.7poundspersquareinch(psi).Thus,atsealevel,agaugepressurereadingof15psiisequaltoanabsolutepressureof29.7psi.ThisrequirementisnotintendedtoapplytostorageofacetylenedissolvedinasuitablesolventincylindersmanufacturedandmaintainedaccordingtoDOTrequirements,ortoacetyleneforchemicaluse.Oxygen-FuelGasWeldingandCutting-IntroductionWhenusingacetylene,experienceindicatesthat15psigisgenerallyacceptableasasafeupperpressurelimit.Usingacetyleneatpressuresinexcessof15psigpressure(orabout30psiapressure)isahazardouspractice.Freegaseousacetyleneispotentiallyunstableatpressuresabove15psigandcoulddecomposewithexplosiveviolence.ThedecompositioncharacteristicsofacetylenegasareavoidedbykeepingthegasinliquidsolutionandstoringitincylindersofuniqueconstructionOxygen-FuelGasWeldingandCutting-IntroductionInternally,acetylenecylindersarenotdesignedlikeotherkindsofcompressedgascylinders.Acetylenecylindersareneverhollow.Thesecylinderscontainaporous,calciumsilicatefillerandasuitablesolvent,usuallyacetone,because,underpressure,acetylenebyitselfisunstable.Acetoneisusedbecauseithastheabilitytoabsorbover400timesitsownvolumeofacetyleneat70F.CalciumSilicateMillionsofmicroscopicporesmakeupthecalciumsilicatefiller.Althoughitappearstofillthesteelshell,approximately90percentofthefillersvolumeconsistsofporespaceforholdingandevenlydistributingtheacetylene/acetonesolution.Whenabsorbedinthisfiller,theacetyleneisdividedintosuchsmallunitsthat,shouldacetylenedecompositiontakeplaceinonepore,theheatreleasedisnotenoughtoraisethetemperatureoftheacetyleneinsurroundingporestothepointwhereit,too,willdecompose.Acetyleneisusuallysuppliedincylinderswhichhaveacapacityofupto300cubicfeetofdissolvedgasunderpressureof250psigat70F.Oxygen-FuelGasWeldingandCutting-CylindersRegardlessoftheinteriorconstructionofthecylinders,allportablecylindersusedforthestorageandshipmentofcompressedgasesshallbeconstructedandmaintainedinaccordancewiththeregulationsoftheU.S.DepartmentofTransportation,49CFRParts171-179.Whenusingorhandlingcylindersandcontainers,itisimportanttoknowabout:lCylinderapprovalandmarkinglStorageofcylinderslOperatingprocedures.Compressedgascylindersshallbelegiblymarked,forthepurposeofidentifyingthegascontent,witheitherthechemicalortradenameofthegas.Suchmarkingshallbebymeansofstenciling,stamping,orlabeling,andshallnotbereadilyremovable.Wheneverpractical,themarkingshallbelocatedontheshoulderofthecylinder.Oxygen-FuelGasWeldingandCutting-CylindersAppropriatemarkingnotonlyenablesproperuse,butalsoassistsinproperstorage.Thefollowinginformationgenerallyappliestoallcylinders:lCylindersshallbekeptawayfromradiatorsandothersourcesofheatlInsideofbuildings,cylindersshallbestoredinawell-protected,well-ventilated,drylocation,atleast20feet(6.1m)fromhighlycombustiblematerials.Cylindersshouldbestoredinassignedplacesawayfromelevators,stairs,organgways,orotherareaswheretheymightbeknockedoverordamagedbypassingorfallingobjects,orsubjecttotamperinglEmptycylindersshallhavetheirvalvesclosedlValveprotectioncaps,wherethecylinderisdesignedtoacceptacap,shallalwaysbeinplace,hand-tight,exceptwhencylindersareinuseorconnectedforuse.Thevalveprotectioncapisdesignedtotaketheblowincasethecylinderfalls.Additionalrequirementsexistforthestorageoffuelgasandoxygencylinders.Fuel Gas Cylinders - Storage RequirementsInsideabuilding,storedcylindersshallbelimitedtoatotalgascapacityof2,000cubicfeet(56m3)or300poundsofliquefiedpetroleumgas.Thislimitationdoesnotapplytocylindersthatareinactualuseorareattachedreadyforuse.Acetylenecylindersshallbestoredvalveendup.Ifthecylinderisonitsside,acetonemayleakoutandcreateadangerouscondition.Oxygen CylindersOxygencylindersinstorageshallbeseparatedfromfuel-gascylindersorcombustiblematerials(especiallyoilorgrease),aminimumdistanceof20feet(6.1m)orbyanon-combustiblebarrieratleast5feet(1.5m)highhavingafire-resistanceratingofatleastone-halfhour.Thisrequirementisintendedtoreducethepossibilityofanyfiresupportwhenafireoccursamongthefuelgasstorage.Oxygen-FuelGasWeldingandCutting-CylindersThepotentialdangersrelatedtocylinderscontainingcompressedgasesrequirethatcylindersbestoredandoperatedproperly.Operationmustemphasizetheabsenceofoilyorgreasysubstances.Followtheserulesofoperation:lCylinders,cylindervalves,couplings,regulators,hose,andapparatusshallbekeptfreefromoilyorgreasysubstanceslOxygencylindersorapparatusshallnotbehandledwithoilyhandsorgloveslAjetofoxygenmustneverbepermittedtostrikeanoilysurface,greasyclothes,orenterafueloilorotherstoragetank.Oxygen-FuelGasWeldingandCutting-CylindersThevalveoutletandregulatoraretwocriticalcomponentsofcompressedgascylindersthatmustbeusedproperly.Valveprotectioncapsprotectthevalvefromdamageandoilandgrease.Thevalve-protectioncapshallnotbeusedforliftingcylindersfromoneverticalpositiontoanother.Thecapmayaccidentallyandsuddenlycomeloose.Shouldacylinderwithoutacapfallorbeknockedover,thevalvemaybedamagedorshearedoff,causingasuddenreleaseofpressure.Ifthevalveoutletofacylinderbecomescloggedwithice,thawwithwarmnotboilingwater.Oxygen-FuelGasWeldingandCutting-CylindersLikethevalveoutlet,theregulatormustbecarefullyprotected.Unlesscylindersaresecuredonaspecialtruck,regulatorsshallberemovedandvalve-protectioncaps,whenprovidedfor,shallbeputinplacebeforecylindersaremoved.Cylindersnothavingfixedhandwheelsshallhavekeys,handles,ornon-adjustablewrenchesonvalvestemswhilethesecylindersareinservice.Unlessconnectedtoamanifold,alwaysattacharegulatortothecompressedgascylinderbeforeuse.Makecertainthattheregulatoriscompatiblefortheparticulargasandservicepressure.Makesuretheregulatoriscleanandhasacleanfilterinstalledintheinletnipple.Oxygen-FuelGasWeldingandCutting-CylindersBeforeattachingtheregulator,removetheprotectivecapfromthecylinder.Standtoonesideofthecylinder.Openthecylindervalveslightlyforaninstant,andthencloseit.Thiscrackingofthecylindervalvewillcleanthevalveofdustordirtwhichmayhaveaccumulatedduringstorage.Dirtcandamagecriticalpartsofaregulator,andmaycauseafireorexplosion.Beforearegulatorisremovedfromacylindervalve,thevalveshallbeclosedandthegasreleasedfromtheregulator.Anacetylenecylindervalveshallnotbeopenedmorethanoneandone-halfturnsofthespindle.Thispermitsadequateflowofacetyleneandallowsreadyclosingofthevalveinanemergencysituation.Oxygen-Fuel Gas Welding and Cutting - Manifolding of CylindersSometimeswhenwelding,aportablecylinderisnotusedasthesourceofgas.Aservicepipesystemcanbeusedtoprovideamanifoldingeffect.Manifoldingisthegatheringofmultiple-linefluidinputsintoasingleintakechamber.Inotherwords,thecombiningofgasesneededforwelding.Thiscanbeaccomplishedthroughtheuseofportableoutletheaders.Eachheaderwillcontroltheflowofaparticulargas.Portableoutletheaders(showninpurple)consistofthenozzleandhosesthatcanbeconnectedtoaportablecylinderoraservicepipe.Portableoutletheadersshallnotbeusedindoorsexceptfortemporaryservicewheretheconditionsprecludeadirectsupplyfromoutletslocatedontheservicepipingsystem.Eachoutletontheservicepipingfromwhichoxygenorfuelgasiswithdrawntosupplyaportableoutletheadershallbeequippedwithareadilyaccessibleshut-offvalve(showninredinthefigure).Oxygen-Fuel Gas Welding and Cutting - Manifolding of CylindersEachserviceoutletonportableoutletheadersshallbeprovidedwithavalveassemblythatincludesadetachableoutletsealcap(showninyellow),chainedorotherwiseattachedtothebodyofthevalve.Theprimaryreasonsforusingasealcaparetoprotecttheoutletpipethreadfromdamageandtopreventthedepositofoilorgreaseonthethreads.Manytimesthecapsarenotused.Failuretousethesealcapcanresultindamagetothreadsandgroundseals.ThiscancauseleakyconnectionsOxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsServicepipingsystemsmustmeetalldesignandinstallationsafetyrequirements.PipeshallbeatleastSchedule40andfittingsshallbeatleaststandardweightinsizesuptoandincluding6-inchnominal.Schedule40pipeisstandardblackironpipewhichhasaworkingpressureofupto125psiandisalwaystestedbeforeuse.Problemsmightarisewhenlineextensionsaremadewithothertypesofpipeoraluminumtubing.Therefore,acloseinspectionisnecessary.Therearespecialrequirementsforservicepipesystemswhenusingoxygenoracetylene.lOxygenlAcetyleneorAcetyleneCompoundslOxygen Whenoxygenissuppliedtoaservicepipingsystemfromalowpressureoxygenmanifoldwithoutaninterveningpressureregulatingdevice,thepipingsystemshallhaveaminimumdesignpressureof250psig.Apressureregulatingdeviceshallbeusedateachstationoutletwhentheconnectedequipmentisforuseatpressureslessthan250psig.lAcetylene or Acetylene Compounds Pipingforacetyleneoracetyleniccompoundsshallbesteelorwroughtiron.Unalloyedcoppershallnotbeusedforacetyleneoracetyleniccompoundsexceptinlistedequipment.Undercertainconditions,acetyleneformsexplosivecompoundswithcopper(aswellassilverandmercury).Oxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsNowthatweunderstandmaterialanddesignrequirements,letsconsidertheinstallationofaservicepipesystem.Allpipingshallberunasdirectlyaspractical.Itwillbeprotectedagainstphysicaldamagewithproperallowanceforexpansion,contraction,jarring,andvibration.Pipelaidundergroundinearthshallbelocatedbelowthefrostlineandprotectedagainstcorrosion.Afterassembly,pipingshallbethoroughlyblownoutwithair,nitrogen,orcarbondioxidetoremoveforeignmaterials.Foroxygenpiping,onlyoil-freeair,oil-freenitrogen,oroil-freecarbondioxideshallbeusedOxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsLowpointsinpipingcarryingmoistgasshallbedrainedintodrippotsconstructedsoastopermitpumpingordrainingoutthecondensateatnecessaryintervals.Drainvalvesforthispurposeshallhaveoutletsclosedwithscrewcapsorplugs.Pipingfromoverheadlinesshallhavedrippotsateachstation.Thesedrippotseitherhaveaplugorpetcockonthebottom.Undergroundinstallationshavenodrainingsystem.Openendvalvesorpetcocksshallbeused.However,drippotslocatedoutofdoors,underground,andnotreadilyaccessible,maybecontrolledbyvalvesiftheyareequippedwithameanstosecurethemintheclosedposition.Pipesleadingtothesurfaceofthegroundshallbecasedorjacketedwherenecessarytopreventlooseningorbreaking.Pipesleadingtothesurfacefromundergroundlineshavetobesecuredtopreventbreakingortoavoidotherdamagetothem.Oxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsAnotherimportantconsiderationforundergroundpipingisprotectionagainstcorrosion.Undergroundpipeandtubingandoutdoorferrouspipeandtubingshallbecoveredorpaintedwithasuitablematerialforprotectionagainstcorrosion.Onceinstallationiscompleted,pipingsystemsshallbetestedandprovedgastightat1timesthemaximumoperatingpressure,andshallbethoroughlypurgedofairbeforebeingplacedinservice.Thematerialusedfortestingoxygenshallbeoilfreeandnon-combustible.Flamesshallnotbeusedtodetectleaks.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionTheentireservicepipesystemmustbeprotectedagainstbuild-upofexcessivepressureandleaks.Thisprotectionisaccomplishedwith:lProtectiveequipmentlRegulatorslProperhoseandhoseconnections.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionProtectiveequipmentisdividedintothetwocategorieslistedhere.lPressureReliefDeviceslPipingProtectiveEquipmentPressure Relief DevicesServicepipingsystemsshallbeprotectedbypressurereliefdevicessettofunctionatnotmorethanthedesignpressureofthesystems.Inaddition,thepressurereliefdeviceshoulddischargeupwardstoasafelocation.Pressurereliefvalvesarerequiredinfuel-gaspipingsystemstopreventexcessivepressurebuildupwithinthesystem.Reliefvalveswillventautomaticallyatpresetpressuresormaybemanuallyoperatedtorelievepressureinthesystem.Piping Protective EquipmentApprovedprotectiveequipmentshallbeinstalledinfuel-gaspipingtoprevent:lBackflowofoxygenintothefuel-gassupplysystemlPassageofaflashbackintothefuel-gassupplysystemlExcessivebackpressureofoxygeninthefuel-gassupplysystem.Thethreefunctionsoftheprotectiveequipmentmaybecombinedinonedeviceormaybeprovidedbyseparatedevices.Theprotectiveequipmentinfuel-gaspipingsystemsshallbelocatedeitheratthemainsupplyline,attheheadofeachbranchline,orateachlocationwherefuel-gasiswithdrawn.Protectiveequipmentplacedatthemainsupplyprovidesthebestprotection.Gotothenextpagetoseeavisualcomparisonofthethreelocationsforsafetydevices.Piping Protective EquipmentProtectiveequipmentcanbelocatedinthemainsupplylinewithonecheckvalveinstalledbeforeeachoutletforthegreatestprotection,asinFigure1,orattheheadofeachbranchlinepluscheckvalvesateachoutlet,asinFigure2,orateachlocationwherefuel-gasiswithdrawnwithcheckvalvesateachoutlet,asinFigure3.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionAnothermethodofcontrollingpressureinvolvestheuseofpressure-reducingregulators.Pressure-reducingregulatorsshallbeusedonlyforthegasandpressuresforwhichtheyareintended.Whenregulatorsorpartsofregulators,includinggages,needrepair,theworkshallbeperformedbyskilledmechanicswhohavebeenproperlyinstructed.Mostproductionshopsdonothavetheproperequipmenttomakerepairs.Foranyequipmentrepairsoriftherearequestionsaboutperformancereliability,contactthemanufacturer.GagesonoxygenregulatorsshallbemarkedUSENOOIL.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionInadditiontousingreleasedevices,thesystemmustbedesigned,usingproperhoses,toprotectagainstleaks.TheOxygenhoseisgreenandhasaright-handthreadednutforconnectingtothetorch.TheAcetylenefuelgashoseisusuallyred(sometimesblack)andhasaleft-handthreadednutforconnectingtothetorch.Hoseandhoseconnectionsshallbeclampedorotherwisesecurelyfastenedinamannerthatwillwithstand,withoutleakage,twicethepressuretowhichtheyarenormallysubjectedinservice,butinnocaselessthanapressureof300psi.Oil-freeairoranoil-freeinertgasshallbeusedforthetest.Hosesshowingleaks,burns,wornplaces,orotherdefectsrenderingitunfitforserviceshallberepairedorreplaced.Wheninspectinghoses,lookforcharredsectionsclosetothetorch.Thesemayhavebeencausedbyflash-back.Alsocheckthathosesarenottapeduptocoverleaks.Arc Welding and Cutting - IntroductionThesecondspecifictypeofweldingdiscussedinthismoduleisArcWeldingandCutting.ThisArcWeldingandCuttingsectionprovidesinformationaboutthethreetopicareasthatarelistedtotheleft.Theinformationpresentedherewillpreventaccidentsandpromoteworksafetywhenundertakingarcweldingorcuttingoperations.Arc Welding and Cutting - IntroductionInthearcweldingprocess,anelectriccurrentpassingthroughtheweldingrodorelectrodeisforcedtojumporarcacrossagap.Theresultingarcproducestheintenseheatnecessaryfortheweldingorcuttingoperation.Arcweldingisusedtofabricatenearlyalltypesofcarbonoralloysteels,thecommonnonferrousmetals,andisindispensableintherepairandreclamationofmetallicmachineparts.Arccuttingisprimarilyusedforroughcutsorforscrappingbecauseoftheunevencutthatresults.Ithasalsobeenusedforunderwatercuttinginsalvagingoperations.Whilemostprecautionsandsafepracticesarecommontooxy-fuelgaswelding,therearesomethatareuniquetoeithergasorarcwelding.Arc Welding and Cutting - IntroductionShieldingisoneoftheuniquerequirementsofarcwelding.Experiencehasshownthatweldswillhavebetterchemicalandphysicalpropertiesiftheaircanbekeptawayfromtheweldpuddle.Suchgasesasoxygen,hydrogen,andnitrogen,alongwithwatervapor(moisture)alltendtoreducethequalityoftheweld.Dirt,dust,andmetaloxides(contaminants)alsoreducetheweldquality.Shieldingofthearcpreservestheintegrityoftheweldjoint.Shieldingisprovidedeitherby:lDecompositionoftheelectrodecovering,knownasfluxlAgas(orgasmixture)whichmayormaynotbeinert.Arc Welding and Cutting - IntroductionArcweldingandcuttinginvolvesavarietyofprocesses.Someofthemorecommonprocessesarelistedbelow.lShieldedMetal-ArcWelding(SMAW)lGasMetalArcWelding(GMAW)lGasTungstenArcWelding(GTAW)lFluxCoredArcWelding(FCAW)lSubmergedArcWelding(SAW)lArcCuttinglPlasmaArcCutting(PAC)lAirCarbon-ArcCutting(AAC)lArcGougingShielded Metal-Arc Welding (SMAW)Shieldedmetal-arcweldingisthemostwidelyusedtypeofarcwelding,commonlyreferredtoasstickwelding.Inthisprocess,coalescenceisachievedbyheatingwithanelectricarcbetweenacovered(orcoated)electrodeandtheworksurface.Shieldingisprovidedbydecompositionoftheelectrodecovering,knownastheflux,whilefillermetalisobtainedfromtheelectrodesmetalcore.Gas Metal Arc Welding (GMAW) GasmetalarcweldingiscommonlyknownasMIGwelding.Inthegasmetalarcweldingprocess,coalescenceisachievedbytheheatofanelectricarcmaintainedbetweentheendofanelectrodeandtheworksurface.Shieldingofthearcisprovidedbyagas(orgasmixture)whichmayormaynotbeinert.Theelectrodeisfedcontinuouslytotheweldwhereitismeltedintheintenseheatofthearcanddepositedasweldmetal.Gas Tungsten Arc Welding (GTAW)GastungstenarcweldingiscommonlyknownasTIGwelding.Ingastungstenarcwelding,coalescenceisachievedbythearcandelectrodemethodexceptthatthetungstenelectrodeisnotconsumed.Shieldingisprovidedbyaninertgas.Thisprocessproduceshighprecisionwelds.Flux Cored Arc Welding (FCAW)Fluxcoredarcweldingisaprocesswhichproducescoalescencebymeansofanarcbetweenacontinuousconsumableelectrodeandtheworksurface.Shieldingisprovidedbyfluxcontainedwithinthetubularelectrode.Additionalshieldingmaybeobtainedfromagasorgasmixture.Submerged Arc Welding (SAW)Insubmergedarcwelding,coalescenceisproducedbytheheatofanarcbetweenabaremetalelectrodeandtheworksurface.Thearcisshieldedbyablanketofgranular,fusibleflux.Thetipoftheelectrodeandtheweldingzonearesurroundedandshieldedbythemoltenfluxandalayerofunusedfluxinthegranularstate.Inthisprocess,thereisnovisibleevidenceofthepassageofcurrentbetweentheelectrodeandtheworksurface.Thiseliminatesthesparks,spatter,andsmokeordinarilyseeninotherarcweldingprocesses.Fumesarestillproduced,butnotinquantitiesgeneratedbyotherprocesses.Arc Cutting Arccuttingisthegeneralprocessinwhichthecuttingorremovalofmetalsisdonebymeltingwiththeheatofanarcbetweenanelectrodeandthebasemetal.Plasma Arc Cutting (PAC) Inplasmaarccutting,themetaliscutbymeltingalocalizedareawithaconstrictedarcandremovingthemoltenmaterialwithahighvelocityjetofhot,ionizedgas.Air Carbon-Arc Cutting (AAC)Aircarbon-arccuttingisatypeofarccuttinginwhichthemetaliscutbymeltingwiththeheatofanarc,withuseofanairstreamtofacilitatecutting.Arc Gouging Arcgougingisanapplicationofarccuttingusedtoproduceagrooveorbevelinthemetalsurface.Arc Welding and Cutting - ApplicationWhenarcwelding,eitheralternatingordirectcurrentisused.TheACandDClimitsshownbelowshallnotbeexceeded.ForACweldingunderwetconditionsorwarmsurroundingswhereperspirationisafactor,theuseofreliableautomaticcontrolsforreducingno-loadvoltageisrecommendedtoreducetheshockhazard.SomeoftheolderACmachinesdonothaveanautomaticcontrolandareonloadallthetime.Itiseasytoreceiveanelectricshockwhentheequipmentisnothandledproperly.AlternatingCurrent(AC)DirectCurrent(DC)Manual80Volts100VoltsAutomatic100Volts100VoltsArc Welding and Cutting - InstallationArcweldingrequiresproperinstallationofequipment.Acriticalpartofinstallationisensuringthatpropergroundingiscompleted.Theframeorcaseoftheweldingmachine(exceptengine-drivenmachines)shallbegroundedundertheconditionsandaccordingtothemethodsprescribedinSubpartS,Electrical.Conduitscontainingelectricalconductorsshallnotbeusedforcompletingawork-leadcircuit.Pipelinesshallnotbeusedasapermanentpartofawork-leadcircuit,butmaybeusedduringconstruction,extension,orrepairprovidingcurrentisnotcarriedthroughthreadedjoints,flangedboltedjoints,orcaulkedjointsandthatspecialprecautionsareusedtoavoidsparkingatconnectionofthework-leadcable.Arc Welding and Cutting - Operation and MaintenanceBeforestartingoperations,allconnectionstothemachineshallbecheckedtomakecertainthattheyareproperlymade.Theworkleadshallbefirmlyattachedtothework.Magneticworkclampsshallbefreefromadherentmetalparticlesofspatteroncontactsurfaces.Coiledweldingcableshallbespreadoutbeforeusetoavoidseriousoverheatinganddamagetoinsulation.Duringweldingoperations,cableswithspliceswithin10feet(3m)oftheholdershallnotbeused.Weldersshouldnotcoilorloopweldingelectrodecablearoundpartsoftheirbody.Cableswithdamagedinsulationorexposedbareconductorsshallbereplaced.Joininglengthsofworkandelectrodecablesshallbedonebytheuseofconnectingmeansspecificallyintendedforthatpurpose.Theconnectingmeansshallhaveinsulationadequatefortheserviceconditions.Resistance WeldingThethirdweldingprocesscoveredinthismoduleisresistancewelding.Resistanceweldingutilizespressureandheatthatisgeneratedinthepiecestobeweldedbyresistancetoanelectriccurrent.Whenconductingresistancewelding,allequipmentshallbeinstalledbyaqualifiedelectricianinconformancewithSubpartS,Electrical.Ifspotandseamweldingmachinesareused,thefollowingprecautionsmustbetaken:lAlldoorsandaccesspanelsofallresistanceweldingmachinesandcontrolpanelsshallbekeptlockedandinterlockedtopreventaccesstoliveportionsoftheequipmentbyunauthorizedpersons.lInallpressweldingoperations,ifthereisapossibilityoftheoperatorsfingersbeingunderthepointofoperation,effectiveguardsmustbeused.Examplesofeffectiveguardsincludeanelectroniceyesafetycircuit,twohandcontrols,orprotectionsimilartothatprescribedforpunchpressoperations.Resistance WeldingThehazardofflyingsparksshallbe,whereverpractical,eliminatedbyinstallingashieldguardofsafetyglassorsuitablefire-resistantplasticatthepointofoperation.Additionalshieldsorcurtainsshallbeinstalledasnecessarytoprotectpassingpersonsfromflyingsparks.Allfootswitchesshallbeguardedtopreventaccidentaloperationofthemachine.Twoormoresafetyemergencystopbuttonsshallbeprovidedonallspecialmulti-spotweldingmachines,including2-postand4-postweldpresses.Additionally,allportableweldingguns,transformersandrelatedequipmentsuspendedfromoverheadstructures,eyebeams,trolleys,etc.,shallbeequippedwithsafetychainsorcables.Safetychainsorcablesshallbecapableofsupportingthetotalshockloadintheeventoffailureofanycomponentofthesupportingsystem.