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1、Welding,CuttingandBrazingIntroductionWelding,cutting,andbrazingareexceptionallydangerous.Compressedgasesareoftenusedtocreateanextremelyhotflame.Differentweldingtechniquescancauseotherhazards.Theweldercanbeinjuredorcausedamagetotheworkareainnumerouswaysincludingfire,explosion,gas,andfumehazards.Goodw
2、orkpracticesmustbefollowedinallwelding,cutting,andbrazingtechniquestopreventinjuries,fires,andexplosions.Thismodulecoversthefollowingsections:lCompressedGaseslGeneralRequirementslOxygen-FuelGasWeldingandCuttinglArcWeldingandCuttinglResistanceWelding.Introduction-ObjectivesAttheendofthisWelding,Cutti
3、ng,andBrazingmodule,youshouldbeableto:lUnderstandthegeneralrequirementsconcerningcompressedgaseslIdentifythegeneralsafetyrequirementsforalltypesofweldinglUnderstandthegeneralcharacteristicsforthevarioustypesofweldinglIdentifythespecificsafetyrequirementsfor:lOxygen-fuelgasweldingandcuttinglArcweldin
4、gandcuttinglResistancewelding.CompressedGases-IntroductionManyweldingandcuttingoperationsrequiretheuseofcompressedgases.Tounderstandthesehazards,wemustunderstandthatcompressedgasesarestoresofpotentialenergy.Ittakesenergytocompressandconfinethegas.Thatenergyisstoreduntilpurposelyreleasedtoperformusef
5、ulworkoruntilaccidentallyreleasedbycontainerfailureorothercauses.Somecompressedgases,acetyleneforexample,havehighflammabilitycharacteristics.Flammablecompressedgases,therefore,haveadditionalstoredenergybesidessimplecompression-releaseenergy.Othercompressedgases,suchasnitrogen,havesimpleasphyxiatingp
6、roperties.Somecompressedgases,suchasoxygen,canaugmentorcompoundfirehazards.CompressedGases-IntroductionCompressedgasesareregulatedbymanystandards.Twoprimarystandardsare:l29CFR1910SubpartQWelding,Cutting,andBrazingcoversthehandling,storage,anduseofcompressedgases,suchasoxygen-fuelgas,whentheyareconsu
7、medintheweldingprocess.l29CFR1910SubpartHHazardousMaterials,1910.101-1910.105coversthegeneralrequirementsforthehandling,storage,anduseofcompressedgasesotherthanthoseconsumedintheweldingprocess.TheGeneralRequirementssectionof1910.101isconcernedwith:lCylinderinspectiontoincluderequiredmarkingslHandlin
8、g,storage,andutilizationlInstallationandmaintenanceofsafetyreliefdevicesCompressedGasesGeneralRequirementsInadditiontotheOccupationalSafetyandHealthAdministration(OSHA)regulationsfoundinSubpartsQandHof29CFR1910thereareotherapplicableregulationsandinformation.TheseincludetheDepartmentofTransportation
9、(DOT)regulations,andtheCompressedGasAssociation(CGA)pamphlets.Thesesourcesprovidetherequirementsforthegeneralcategoryofcompressedgasesandcertainspecificcompressedgases.Animportantaspectoftheseregulationsisthesafetyofcompressedgasstoragecontainers.Specificrequirementsaremadeofemployersfortheinspectio
10、nofthecompressedgascylinders.Visualinspectionsarerequiredtoensurethatthecylindersaresafe.Thenextpagewillgointomoredetailregardingvisualexaminationsofcompressedgasstoragecontainersandthesafetyofthesecontainers.CompressedGasesGeneralRequirementsEmployeesshalldeterminethatcompressedgascylindersunderthe
11、ircontrolareinasafeconditiontotheextentthatthiscanbedeterminedbyvisualinspection.Visualandotherinspectionsarerequired,butotherinspectionsarenotdefined.TheseinspectionsmustbeconductedasprescribedintheHazardousMaterialsRegulationsoftheDOTcontainedin49CFRParts171-179and14CFRPart103.Wheretheseregulation
12、sarenotapplicable,theseinspectionsshallbeconductedinaccordancewithCGAPamphletsC-6andC-8.AccordingtoDOTregulations:Acylinderthatleaks,isbulged,hasdefectivevalvesorsafetydevices,bearsevidenceofphysicalabuse,fireorheatdamage,ordetrimentalrustingorcorrosion,mustnotbeusedunlessitisproperlyrepairedandrequ
13、alifiedasprescribedintheseregulations.Thetermcylinderisdefinedasapressurevesseldesignedforpressureshigherthan40psia(poundspersquareinchabsolute)andhavingacircularcrosssection.Itdoesnotincludeaportabletank,multi-unittankcartank,cargotank,ortankcar.DOTMarkingRequirementsEachDOTmarkingidentifiedonthisp
14、agemustappearonallcylindersandmustbemaintainedsothatitislegible.Thecirclednumbersonthegraphiccorrespondtothenumbereddefinitionsprovidedbelow.1.ICCorDOTmarkingmayappear:ICC:Pre-existingmarkingICC3AA20153AA-specificationfrom49CFR178.372015-markedservicepressure.DOT:newmanufacturemarkingmustreadDOT.49C
15、FR171.14.2.A35798641:Serialnumber-noduplicationspermittedwithanyparticularsymbol-serialnumbercombinations.3.PST:Symbolofmanufacturer,user,orpurchaser.4.656:dateofmanufacture.Monthandyear.:disinterestedinspectorsofficialmark.5.+:indicatescylindermaybe10%overchargedper49CFR173.302(c).6.5-61and5-66:Ret
16、estdates.7.*(5pointedstar0:indicatestenyearretestinterval.See49CFR173.34(e)(15).CompressedGasesGeneralRequirementsInadditiontotheguidanceintheOSHAregulations,CompressedGasAssociation(CGA)pamphletsdeterminerequirementsforhandling,storing,andusingcompressedgasesincylinders,portabletanks,railtankcars,a
17、ndmotorvehiclecargotanks.Theyalsoidentifyhowtoinstallandmaintainrequiredpressurereliefvalvesonthesecontainers.Thein-planthandling,storage,andutilizationofallcompressedgasesincylinders,portabletanks,railtankcars,andmotorvehiclecargotanksshallbeinaccordancewithCGAPamphletP-1.Compressedgascylinders,por
18、tabletanks,andcargotanksshallhavepressurereliefdevicesinstalledandmaintainedinaccordancewithCGAPamphletsS-1.1andS-1.2.CompressedGasesSpecificGasesTheOSHAregulationscontainsomesectionsregulatingspecificcompressedgases,including:lAcetylenelHydrogenlOxygenlNitrousoxidelAnhydrousammonialLiquefiedpetrole
19、umgases.OthercompressedgasesareincommonuseandfallunderregulationSubpartH,1910.101.Examplesincludechlorine,vinylchloride,sulfurdioxide,methylchloride,hydrogensulfide,ethane,compressedair,andnitrogen.GeneralRequirements-IntroductionTheGeneralRequirementssection,1910.252providesinformationaboutprotecti
20、ngindividualsduringwelding,cutting,orbrazingoperations.Thissectioncontainsthethreetopicslistedontheleft.Protectionoftheindividualincludesmeasurestakento:lPreventfiresfromoccurringlEliminatefiresiftheyoccurlProtectpersonnelbyprovidingappropriateclothingandequipmentlProtectpersonnelwhenweldingorcuttin
21、gcontainerslProtectpersonnelworkinginconfinedspaces.GeneralRequirementsFirePreventionandProtectionFirepreventionandprotectionincludebasicprecautions,specialprecautions,andsafetyprecautionsfortheuniquesituationsinvolvingweldingandcuttingcontainers,andweldinginconfinedspaces.Thebasicprecautionsforfire
22、preventioninwelding,cutting,andbrazingfocusonremovaloffirehazards.Theyincludethefollowing:lIftheobjecttobeweldedorcutcannotreadilybemoved,allmovablefirehazardsinthevicinityshallbetakentoasafeplacelIftheobjecttobeweldedorcutcannotbemovedandifallthefirehazardscannotberemoved,thenguardsshallbeusedtocon
23、finetheheat,sparks,andslag,andtoprotecttheimmovablefirehazardslIftheaboverequirementscannotbemet,thenweldingandcuttingshallnotbeperformed.GeneralRequirementsFirePreventionandProtectionComplyingwiththebasicprecautionsforpreventionoffiresinweldingisnotenough.Specialprecautionsmustalsobetaken.Theseincl
24、udehavingtheproperfireextinguishingequipmentavailableandhavingfirewatcherspresent,ifneeded.Suitablefireextinguishingequipmentshallbemaintainedinastateofreadinessforinstantuse.Suchequipmentmayconsistofpailsofwater,bucketsofsand,hoses,orportableextinguishersdependinguponthenatureandquantityofthecombus
25、tiblematerialexposed.Firewatchersarerequiredwheneverweldingorcuttingisperformedinlocationswheremorethanaminorfiremightdevelop,orwhereanyofthefollowingconditionsexist:lAppreciablecombustiblematerials,inbuildingconstructionorcontents,closerthan35feettothepointofoperationlAppreciablecombustiblematerial
26、smorethan35feetaway,butareeasilyignitedbysparks.Afirewatchshallbemaintainedforatleastahalfhouraftercompletionofweldingorcuttingoperationstodetectandextinguishpossiblesmolderingfires.GeneralRequirementsFirePreventionandProtectionEvenifallofthespecialprecautionshavebeentaken,therearestillcertainsituat
27、ionsinwhichwelding,cutting,orbrazingarenotallowed.Cuttingorweldingshallnotbepermittedin:lAreasnotauthorizedbymanagementlBuildingswithimpairedsprinklersystemslThepresenceofexplosiveatmospheres(mixturesofflammablegases,vapors,liquids,ordustswithair)lLocationswhereexplosiveatmospheresmaydevelop,suchas:
28、lInsideuncleanorimproperlypreparedtanksorequipmentwhichhavepreviouslycontainedsuchmaterials(flammablegasses,vapors,liquids,ordusts)lAreaswithanaccumulationofcombustibledusts.GeneralRequirementsFirePreventionandProtectionWeldingandcuttingcertaincontainersmayconstituteaspecialsituationthatrequiresaddi
29、tionalsafetyprecautionsbeyondbasicandspecialprecautions.Nowelding,cutting,orotherhotworkshallbeperformedonuseddrums,barrels,tanks,orothercontainersuntiltheyhavebeenthoroughlycleaned.Cleaningmustremoveallflammablematerialspresentoranysubstancessuchasgreases,tars,acids,orothermaterialswhichmightproduc
30、eflammableortoxicvaporswhensubjectedtoheat.Anypipelineorconnectionstothedrumorvesselbeingweldedshallbedisconnectedorblanked.GeneralRequirementsFirePreventionandProtectionWorkinginconfinedspacesinvolvesadditionalsafetyprecautionsbeyondthebasicandspecialprecautions.Aconfinedspaceisdefinedin29CFR1910.2
31、52asarelativelysmallorrestrictedspacesuchasatank,boiler,pressurevessel,orsmallcompartmentofaship.Adequateventilationisaprerequisitetoworkinconfinedspaces.Whenweldingorcuttingisbeingperformedinanyconfinedspace,thegascylindersandweldingmachinesshallbeleftontheoutside.Whenarcweldingistobesuspendedforan
32、ysubstantialperiodoftime,suchasduringlunchorovernight,allelectrodesshallberemovedfromtheholders.Theholdersshallbecarefullylocatedsothataccidentalcontactcannotoccurandthemachineshallbedisconnectedfromthepowersource.GeneralRequirementsFirePreventionandProtectionWhensuspendinggasweldingorcuttingoperati
33、ons,eliminatethepossibilityofgasescapingthroughthenozzlebyclosingthetorchvalves.Thegassupplytothetorchmustbepositivelyshutoffatsomepointoutsidetheconfinedareawheneverthetorchisnottobeusedforasubstantialperiodoftime,suchasduringlunchhourorovernight.Wherepracticable,thetorchandhoseshallalsoberemovedfr
34、omtheconfinedspace.Whereweldersmustenteraconfinedspacethroughamanholeorothersmallopening,meansshallbeprovidedforquicklyremovingthemincaseofemergency.Anattendantwithapre-plannedrescueprocedureshallbestationedoutsidetoobservethewelderatalltimesandshallbecapableofputtingrescueoperationsintoeffect.Gener
35、alRequirementsProtectionofPersonnelProtectionofpersonnelfocusesonprotectingthewelderfromhazardsotherthangeneralfireprotection.Protectionofpersonnelinweldingorcuttingoperationscaninvolvefallprotection,eyeprotection,andprotectiveclothing.Whenworkingatheights,awelderorhelperworkingonplatforms,scaffolds
36、,orrunwaysshallbeprotectedagainstfallingthroughtheuseof:lRailingslSafetybeltslLifelineslSomeequallyeffectivesafeguards.GeneralRequirementsProtectionofPersonnelWelding,cutting,orbrazingoperationsconductedwithoutpropereyeprotectioncreateaseriouseyeinjuryhazard.Helmetsandhandshieldsshallbearrangedtopro
37、tecttheface,neck,andearsfromdirectradiantenergyfromthearc.Theyshallbeusedduringallarcweldingorarccuttingoperations,excludingsubmergedarcwelding.helpersorattendantsshallbeprovidedwithpropereyeprotection.Helmetsandhandshieldsshallbemadeofamaterialwhichisaninsulatorforheatandelectricity.Helmets,shields
38、,andgogglesshallnotbereadilyflammableandshallbecapableofwithstandingsterilization.Wheretheworkpermits,theweldershouldbeenclosedinanindividualboothorinanon-combustiblescreenpaintedwithafinishoflowreflectivitysuchaszincoxide(animportantfactorforabsorbingultra-violetradiation)andlampblack.Boothsandscre
39、ensshallpermitcirculationofairatfloorlevel.Peopleadjacenttotheweldingareasshallbeprotectedfromtheraysbynon-combustibleorflameproofscreensorshieldsorshallberequiredtowearappropriategoggles.GeneralRequirementsProtectionofPersonnelBecauseofthedangerofburnsandclothingcatchingfire,employeesexposedtotheha
40、zardscreatedbywelding,cutting,orbrazingoperationsshallbeprotectedbypersonalprotectiveequipmentinaccordancewiththerequirementsof29CFR1910.132.Appropriateprotectiveclothingrequiredforanyweldingoperationwillvarywiththesize,nature,andlocationoftheworktobeperformed.Weldersshouldalwaysselectclothingmateri
41、alswhichwillprovidemaximumprotectionfromsparksandhotmetal.Theshirtshouldhavefullsleeves,nopockets,andshouldbewornoutsidethetrouserswithcollarbuttoned.Thetrousersshouldhavenocuffsandshouldextendwelldowntothesafetyshoes.Safetyshoesandfire-resistantgauntletglovesarealsoneeded.GeneralRequirementsHealthP
42、rotectionsandVentilationRegardlessoftheprecautionarymeasurestaken,somematerialsrequirespecialventilationbecausetheyareparticularlyhazardous.Mechanicalventilationandotherspecificcontrolmeasuresarerequiredwhenweldingorcuttingisdonewiththefollowingmaterials:lFluorinecompoundslZinclLeadlBerylliumlCadmiu
43、mlMercurylCleaningcompoundslStainlesssteelOxygen-FuelGasWeldingandCutting-IntroductionInthisWelding,Cutting,andBrazingmodule,threespecifictypesofweldingarecovered.Thesearelistedbelow:lOxygen-fuelgasweldingandcuttinglArcweldingandcuttinglResistancewelding.Thissectiondealsspecificallywithoxygen-fuelga
44、sweldingandcutting.TheOxygen-FuelGasWeldingandCuttingsectionisbasedon29CFR1910.253.Thissectionprovidesinformationaboutthefivetopicareasthatarelistedtotheleft.Eachtopicispresentedwithguidanceinformationsothatyouwillbeabletopreventaccidentsandpromoteworksafetywhenweldingorcutting.Oxygen-FuelGasWelding
45、andCutting-IntroductionGeneralRequirementsofOxygen-FuelGasWeldingandCutting,29CFR1910.253,focusesonusingacetylenesafely.Undernoconditionsshallacetylenebegenerated,piped(exceptinapprovedcylindermanifolds),orutilizedatapressureinexcessof15poundspersquareinchgauge(psig)or30poundspersquareinchabsolute(p
46、sia).The30psialimitisintendedtopreventunsafeuseofacetyleneinpressurizedchamberssuchascaissons,undergroundexcavations,ortunnelconstruction.Absolutepressureisequaltogaugepressureplusatmosphericpressure,whichatsealevelaverages14.7poundspersquareinch(psi).Thus,atsealevel,agaugepressurereadingof15psiiseq
47、ualtoanabsolutepressureof29.7psi.ThisrequirementisnotintendedtoapplytostorageofacetylenedissolvedinasuitablesolventincylindersmanufacturedandmaintainedaccordingtoDOTrequirements,ortoacetyleneforchemicaluse.Oxygen-FuelGasWeldingandCutting-IntroductionWhenusingacetylene,experienceindicatesthat15psigis
48、generallyacceptableasasafeupperpressurelimit.Usingacetyleneatpressuresinexcessof15psigpressure(orabout30psiapressure)isahazardouspractice.Freegaseousacetyleneispotentiallyunstableatpressuresabove15psigandcoulddecomposewithexplosiveviolence.Thedecompositioncharacteristicsofacetylenegasareavoidedbykee
49、pingthegasinliquidsolutionandstoringitincylindersofuniqueconstructionOxygen-FuelGasWeldingandCutting-IntroductionInternally,acetylenecylindersarenotdesignedlikeotherkindsofcompressedgascylinders.Acetylenecylindersareneverhollow.Thesecylinderscontainaporous,calciumsilicatefillerandasuitablesolvent,us
50、uallyacetone,because,underpressure,acetylenebyitselfisunstable.Acetoneisusedbecauseithastheabilitytoabsorbover400timesitsownvolumeofacetyleneat70F.CalciumSilicateMillionsofmicroscopicporesmakeupthecalciumsilicatefiller.Althoughitappearstofillthesteelshell,approximately90percentofthefillersvolumecons
51、istsofporespaceforholdingandevenlydistributingtheacetylene/acetonesolution.Whenabsorbedinthisfiller,theacetyleneisdividedintosuchsmallunitsthat,shouldacetylenedecompositiontakeplaceinonepore,theheatreleasedisnotenoughtoraisethetemperatureoftheacetyleneinsurroundingporestothepointwhereit,too,willdeco
52、mpose.Acetyleneisusuallysuppliedincylinderswhichhaveacapacityofupto300cubicfeetofdissolvedgasunderpressureof250psigat70F.Oxygen-FuelGasWeldingandCutting-CylindersRegardlessoftheinteriorconstructionofthecylinders,allportablecylindersusedforthestorageandshipmentofcompressedgasesshallbeconstructedandma
53、intainedinaccordancewiththeregulationsoftheU.S.DepartmentofTransportation,49CFRParts171-179.Whenusingorhandlingcylindersandcontainers,itisimportanttoknowabout:lCylinderapprovalandmarkinglStorageofcylinderslOperatingprocedures.Compressedgascylindersshallbelegiblymarked,forthepurposeofidentifyingthega
54、scontent,witheitherthechemicalortradenameofthegas.Suchmarkingshallbebymeansofstenciling,stamping,orlabeling,andshallnotbereadilyremovable.Wheneverpractical,themarkingshallbelocatedontheshoulderofthecylinder.Oxygen-FuelGasWeldingandCutting-CylindersAppropriatemarkingnotonlyenablesproperuse,butalsoass
55、istsinproperstorage.Thefollowinginformationgenerallyappliestoallcylinders:lCylindersshallbekeptawayfromradiatorsandothersourcesofheatlInsideofbuildings,cylindersshallbestoredinawell-protected,well-ventilated,drylocation,atleast20feet(6.1m)fromhighlycombustiblematerials.Cylindersshouldbestoredinassig
56、nedplacesawayfromelevators,stairs,organgways,orotherareaswheretheymightbeknockedoverordamagedbypassingorfallingobjects,orsubjecttotamperinglEmptycylindersshallhavetheirvalvesclosedlValveprotectioncaps,wherethecylinderisdesignedtoacceptacap,shallalwaysbeinplace,hand-tight,exceptwhencylindersareinuseo
57、rconnectedforuse.Thevalveprotectioncapisdesignedtotaketheblowincasethecylinderfalls.Additionalrequirementsexistforthestorageoffuelgasandoxygencylinders.Fuel Gas Cylinders - Storage RequirementsInsideabuilding,storedcylindersshallbelimitedtoatotalgascapacityof2,000cubicfeet(56m3)or300poundsofliquefie
58、dpetroleumgas.Thislimitationdoesnotapplytocylindersthatareinactualuseorareattachedreadyforuse.Acetylenecylindersshallbestoredvalveendup.Ifthecylinderisonitsside,acetonemayleakoutandcreateadangerouscondition.Oxygen CylindersOxygencylindersinstorageshallbeseparatedfromfuel-gascylindersorcombustiblemat
59、erials(especiallyoilorgrease),aminimumdistanceof20feet(6.1m)orbyanon-combustiblebarrieratleast5feet(1.5m)highhavingafire-resistanceratingofatleastone-halfhour.Thisrequirementisintendedtoreducethepossibilityofanyfiresupportwhenafireoccursamongthefuelgasstorage.Oxygen-FuelGasWeldingandCutting-Cylinder
60、sThepotentialdangersrelatedtocylinderscontainingcompressedgasesrequirethatcylindersbestoredandoperatedproperly.Operationmustemphasizetheabsenceofoilyorgreasysubstances.Followtheserulesofoperation:lCylinders,cylindervalves,couplings,regulators,hose,andapparatusshallbekeptfreefromoilyorgreasysubstance
61、slOxygencylindersorapparatusshallnotbehandledwithoilyhandsorgloveslAjetofoxygenmustneverbepermittedtostrikeanoilysurface,greasyclothes,orenterafueloilorotherstoragetank.Oxygen-FuelGasWeldingandCutting-CylindersThevalveoutletandregulatoraretwocriticalcomponentsofcompressedgascylindersthatmustbeusedpr
62、operly.Valveprotectioncapsprotectthevalvefromdamageandoilandgrease.Thevalve-protectioncapshallnotbeusedforliftingcylindersfromoneverticalpositiontoanother.Thecapmayaccidentallyandsuddenlycomeloose.Shouldacylinderwithoutacapfallorbeknockedover,thevalvemaybedamagedorshearedoff,causingasuddenreleaseofp
63、ressure.Ifthevalveoutletofacylinderbecomescloggedwithice,thawwithwarmnotboilingwater.Oxygen-FuelGasWeldingandCutting-CylindersLikethevalveoutlet,theregulatormustbecarefullyprotected.Unlesscylindersaresecuredonaspecialtruck,regulatorsshallberemovedandvalve-protectioncaps,whenprovidedfor,shallbeputinp
64、lacebeforecylindersaremoved.Cylindersnothavingfixedhandwheelsshallhavekeys,handles,ornon-adjustablewrenchesonvalvestemswhilethesecylindersareinservice.Unlessconnectedtoamanifold,alwaysattacharegulatortothecompressedgascylinderbeforeuse.Makecertainthattheregulatoriscompatiblefortheparticulargasandser
65、vicepressure.Makesuretheregulatoriscleanandhasacleanfilterinstalledintheinletnipple.Oxygen-FuelGasWeldingandCutting-CylindersBeforeattachingtheregulator,removetheprotectivecapfromthecylinder.Standtoonesideofthecylinder.Openthecylindervalveslightlyforaninstant,andthencloseit.Thiscrackingofthecylinder
66、valvewillcleanthevalveofdustordirtwhichmayhaveaccumulatedduringstorage.Dirtcandamagecriticalpartsofaregulator,andmaycauseafireorexplosion.Beforearegulatorisremovedfromacylindervalve,thevalveshallbeclosedandthegasreleasedfromtheregulator.Anacetylenecylindervalveshallnotbeopenedmorethanoneandone-halft
67、urnsofthespindle.Thispermitsadequateflowofacetyleneandallowsreadyclosingofthevalveinanemergencysituation.Oxygen-Fuel Gas Welding and Cutting - Manifolding of CylindersSometimeswhenwelding,aportablecylinderisnotusedasthesourceofgas.Aservicepipesystemcanbeusedtoprovideamanifoldingeffect.Manifoldingist
68、hegatheringofmultiple-linefluidinputsintoasingleintakechamber.Inotherwords,thecombiningofgasesneededforwelding.Thiscanbeaccomplishedthroughtheuseofportableoutletheaders.Eachheaderwillcontroltheflowofaparticulargas.Portableoutletheaders(showninpurple)consistofthenozzleandhosesthatcanbeconnectedtoapor
69、tablecylinderoraservicepipe.Portableoutletheadersshallnotbeusedindoorsexceptfortemporaryservicewheretheconditionsprecludeadirectsupplyfromoutletslocatedontheservicepipingsystem.Eachoutletontheservicepipingfromwhichoxygenorfuelgasiswithdrawntosupplyaportableoutletheadershallbeequippedwithareadilyacce
70、ssibleshut-offvalve(showninredinthefigure).Oxygen-Fuel Gas Welding and Cutting - Manifolding of CylindersEachserviceoutletonportableoutletheadersshallbeprovidedwithavalveassemblythatincludesadetachableoutletsealcap(showninyellow),chainedorotherwiseattachedtothebodyofthevalve.Theprimaryreasonsforusin
71、gasealcaparetoprotecttheoutletpipethreadfromdamageandtopreventthedepositofoilorgreaseonthethreads.Manytimesthecapsarenotused.Failuretousethesealcapcanresultindamagetothreadsandgroundseals.ThiscancauseleakyconnectionsOxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsServicepipingsystemsmustme
72、etalldesignandinstallationsafetyrequirements.PipeshallbeatleastSchedule40andfittingsshallbeatleaststandardweightinsizesuptoandincluding6-inchnominal.Schedule40pipeisstandardblackironpipewhichhasaworkingpressureofupto125psiandisalwaystestedbeforeuse.Problemsmightarisewhenlineextensionsaremadewithothe
73、rtypesofpipeoraluminumtubing.Therefore,acloseinspectionisnecessary.Therearespecialrequirementsforservicepipesystemswhenusingoxygenoracetylene.lOxygenlAcetyleneorAcetyleneCompoundslOxygen Whenoxygenissuppliedtoaservicepipingsystemfromalowpressureoxygenmanifoldwithoutaninterveningpressureregulatingdev
74、ice,thepipingsystemshallhaveaminimumdesignpressureof250psig.Apressureregulatingdeviceshallbeusedateachstationoutletwhentheconnectedequipmentisforuseatpressureslessthan250psig.lAcetylene or Acetylene Compounds Pipingforacetyleneoracetyleniccompoundsshallbesteelorwroughtiron.Unalloyedcoppershallnotbeu
75、sedforacetyleneoracetyleniccompoundsexceptinlistedequipment.Undercertainconditions,acetyleneformsexplosivecompoundswithcopper(aswellassilverandmercury).Oxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsNowthatweunderstandmaterialanddesignrequirements,letsconsidertheinstallationofaservicepipe
76、system.Allpipingshallberunasdirectlyaspractical.Itwillbeprotectedagainstphysicaldamagewithproperallowanceforexpansion,contraction,jarring,andvibration.Pipelaidundergroundinearthshallbelocatedbelowthefrostlineandprotectedagainstcorrosion.Afterassembly,pipingshallbethoroughlyblownoutwithair,nitrogen,o
77、rcarbondioxidetoremoveforeignmaterials.Foroxygenpiping,onlyoil-freeair,oil-freenitrogen,oroil-freecarbondioxideshallbeusedOxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsLowpointsinpipingcarryingmoistgasshallbedrainedintodrippotsconstructedsoastopermitpumpingordrainingoutthecondensateatnec
78、essaryintervals.Drainvalvesforthispurposeshallhaveoutletsclosedwithscrewcapsorplugs.Pipingfromoverheadlinesshallhavedrippotsateachstation.Thesedrippotseitherhaveaplugorpetcockonthebottom.Undergroundinstallationshavenodrainingsystem.Openendvalvesorpetcocksshallbeused.However,drippotslocatedoutofdoors
79、,underground,andnotreadilyaccessible,maybecontrolledbyvalvesiftheyareequippedwithameanstosecurethemintheclosedposition.Pipesleadingtothesurfaceofthegroundshallbecasedorjacketedwherenecessarytopreventlooseningorbreaking.Pipesleadingtothesurfacefromundergroundlineshavetobesecuredtopreventbreakingortoa
80、voidotherdamagetothem.Oxygen-Fuel Gas Welding and Cutting - Service Pipe SystemsAnotherimportantconsiderationforundergroundpipingisprotectionagainstcorrosion.Undergroundpipeandtubingandoutdoorferrouspipeandtubingshallbecoveredorpaintedwithasuitablematerialforprotectionagainstcorrosion.Onceinstallati
81、oniscompleted,pipingsystemsshallbetestedandprovedgastightat1timesthemaximumoperatingpressure,andshallbethoroughlypurgedofairbeforebeingplacedinservice.Thematerialusedfortestingoxygenshallbeoilfreeandnon-combustible.Flamesshallnotbeusedtodetectleaks.Oxygen-Fuel Gas Welding and Cutting - Pipe System P
82、rotectionTheentireservicepipesystemmustbeprotectedagainstbuild-upofexcessivepressureandleaks.Thisprotectionisaccomplishedwith:lProtectiveequipmentlRegulatorslProperhoseandhoseconnections.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionProtectiveequipmentisdividedintothetwocategoriesliste
83、dhere.lPressureReliefDeviceslPipingProtectiveEquipmentPressure Relief DevicesServicepipingsystemsshallbeprotectedbypressurereliefdevicessettofunctionatnotmorethanthedesignpressureofthesystems.Inaddition,thepressurereliefdeviceshoulddischargeupwardstoasafelocation.Pressurereliefvalvesarerequiredinfue
84、l-gaspipingsystemstopreventexcessivepressurebuildupwithinthesystem.Reliefvalveswillventautomaticallyatpresetpressuresormaybemanuallyoperatedtorelievepressureinthesystem.Piping Protective EquipmentApprovedprotectiveequipmentshallbeinstalledinfuel-gaspipingtoprevent:lBackflowofoxygenintothefuel-gassup
85、plysystemlPassageofaflashbackintothefuel-gassupplysystemlExcessivebackpressureofoxygeninthefuel-gassupplysystem.Thethreefunctionsoftheprotectiveequipmentmaybecombinedinonedeviceormaybeprovidedbyseparatedevices.Theprotectiveequipmentinfuel-gaspipingsystemsshallbelocatedeitheratthemainsupplyline,atthe
86、headofeachbranchline,orateachlocationwherefuel-gasiswithdrawn.Protectiveequipmentplacedatthemainsupplyprovidesthebestprotection.Gotothenextpagetoseeavisualcomparisonofthethreelocationsforsafetydevices.Piping Protective EquipmentProtectiveequipmentcanbelocatedinthemainsupplylinewithonecheckvalveinsta
87、lledbeforeeachoutletforthegreatestprotection,asinFigure1,orattheheadofeachbranchlinepluscheckvalvesateachoutlet,asinFigure2,orateachlocationwherefuel-gasiswithdrawnwithcheckvalvesateachoutlet,asinFigure3.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionAnothermethodofcontrollingpressurein
88、volvestheuseofpressure-reducingregulators.Pressure-reducingregulatorsshallbeusedonlyforthegasandpressuresforwhichtheyareintended.Whenregulatorsorpartsofregulators,includinggages,needrepair,theworkshallbeperformedbyskilledmechanicswhohavebeenproperlyinstructed.Mostproductionshopsdonothavetheproperequ
89、ipmenttomakerepairs.Foranyequipmentrepairsoriftherearequestionsaboutperformancereliability,contactthemanufacturer.GagesonoxygenregulatorsshallbemarkedUSENOOIL.Oxygen-Fuel Gas Welding and Cutting - Pipe System ProtectionInadditiontousingreleasedevices,thesystemmustbedesigned,usingproperhoses,toprotec
90、tagainstleaks.TheOxygenhoseisgreenandhasaright-handthreadednutforconnectingtothetorch.TheAcetylenefuelgashoseisusuallyred(sometimesblack)andhasaleft-handthreadednutforconnectingtothetorch.Hoseandhoseconnectionsshallbeclampedorotherwisesecurelyfastenedinamannerthatwillwithstand,withoutleakage,twiceth
91、epressuretowhichtheyarenormallysubjectedinservice,butinnocaselessthanapressureof300psi.Oil-freeairoranoil-freeinertgasshallbeusedforthetest.Hosesshowingleaks,burns,wornplaces,orotherdefectsrenderingitunfitforserviceshallberepairedorreplaced.Wheninspectinghoses,lookforcharredsectionsclosetothetorch.T
92、hesemayhavebeencausedbyflash-back.Alsocheckthathosesarenottapeduptocoverleaks.Arc Welding and Cutting - IntroductionThesecondspecifictypeofweldingdiscussedinthismoduleisArcWeldingandCutting.ThisArcWeldingandCuttingsectionprovidesinformationaboutthethreetopicareasthatarelistedtotheleft.Theinformation
93、presentedherewillpreventaccidentsandpromoteworksafetywhenundertakingarcweldingorcuttingoperations.Arc Welding and Cutting - IntroductionInthearcweldingprocess,anelectriccurrentpassingthroughtheweldingrodorelectrodeisforcedtojumporarcacrossagap.Theresultingarcproducestheintenseheatnecessaryfortheweld
94、ingorcuttingoperation.Arcweldingisusedtofabricatenearlyalltypesofcarbonoralloysteels,thecommonnonferrousmetals,andisindispensableintherepairandreclamationofmetallicmachineparts.Arccuttingisprimarilyusedforroughcutsorforscrappingbecauseoftheunevencutthatresults.Ithasalsobeenusedforunderwatercuttingin
95、salvagingoperations.Whilemostprecautionsandsafepracticesarecommontooxy-fuelgaswelding,therearesomethatareuniquetoeithergasorarcwelding.Arc Welding and Cutting - IntroductionShieldingisoneoftheuniquerequirementsofarcwelding.Experiencehasshownthatweldswillhavebetterchemicalandphysicalpropertiesiftheai
96、rcanbekeptawayfromtheweldpuddle.Suchgasesasoxygen,hydrogen,andnitrogen,alongwithwatervapor(moisture)alltendtoreducethequalityoftheweld.Dirt,dust,andmetaloxides(contaminants)alsoreducetheweldquality.Shieldingofthearcpreservestheintegrityoftheweldjoint.Shieldingisprovidedeitherby:lDecompositionoftheel
97、ectrodecovering,knownasfluxlAgas(orgasmixture)whichmayormaynotbeinert.Arc Welding and Cutting - IntroductionArcweldingandcuttinginvolvesavarietyofprocesses.Someofthemorecommonprocessesarelistedbelow.lShieldedMetal-ArcWelding(SMAW)lGasMetalArcWelding(GMAW)lGasTungstenArcWelding(GTAW)lFluxCoredArcWeld
98、ing(FCAW)lSubmergedArcWelding(SAW)lArcCuttinglPlasmaArcCutting(PAC)lAirCarbon-ArcCutting(AAC)lArcGougingShielded Metal-Arc Welding (SMAW)Shieldedmetal-arcweldingisthemostwidelyusedtypeofarcwelding,commonlyreferredtoasstickwelding.Inthisprocess,coalescenceisachievedbyheatingwithanelectricarcbetweenac
99、overed(orcoated)electrodeandtheworksurface.Shieldingisprovidedbydecompositionoftheelectrodecovering,knownastheflux,whilefillermetalisobtainedfromtheelectrodesmetalcore.Gas Metal Arc Welding (GMAW) GasmetalarcweldingiscommonlyknownasMIGwelding.Inthegasmetalarcweldingprocess,coalescenceisachievedbythe
100、heatofanelectricarcmaintainedbetweentheendofanelectrodeandtheworksurface.Shieldingofthearcisprovidedbyagas(orgasmixture)whichmayormaynotbeinert.Theelectrodeisfedcontinuouslytotheweldwhereitismeltedintheintenseheatofthearcanddepositedasweldmetal.Gas Tungsten Arc Welding (GTAW)Gastungstenarcweldingisc
101、ommonlyknownasTIGwelding.Ingastungstenarcwelding,coalescenceisachievedbythearcandelectrodemethodexceptthatthetungstenelectrodeisnotconsumed.Shieldingisprovidedbyaninertgas.Thisprocessproduceshighprecisionwelds.Flux Cored Arc Welding (FCAW)Fluxcoredarcweldingisaprocesswhichproducescoalescencebymeanso
102、fanarcbetweenacontinuousconsumableelectrodeandtheworksurface.Shieldingisprovidedbyfluxcontainedwithinthetubularelectrode.Additionalshieldingmaybeobtainedfromagasorgasmixture.Submerged Arc Welding (SAW)Insubmergedarcwelding,coalescenceisproducedbytheheatofanarcbetweenabaremetalelectrodeandtheworksurf
103、ace.Thearcisshieldedbyablanketofgranular,fusibleflux.Thetipoftheelectrodeandtheweldingzonearesurroundedandshieldedbythemoltenfluxandalayerofunusedfluxinthegranularstate.Inthisprocess,thereisnovisibleevidenceofthepassageofcurrentbetweentheelectrodeandtheworksurface.Thiseliminatesthesparks,spatter,and
104、smokeordinarilyseeninotherarcweldingprocesses.Fumesarestillproduced,butnotinquantitiesgeneratedbyotherprocesses.Arc Cutting Arccuttingisthegeneralprocessinwhichthecuttingorremovalofmetalsisdonebymeltingwiththeheatofanarcbetweenanelectrodeandthebasemetal.Plasma Arc Cutting (PAC) Inplasmaarccutting,th
105、emetaliscutbymeltingalocalizedareawithaconstrictedarcandremovingthemoltenmaterialwithahighvelocityjetofhot,ionizedgas.Air Carbon-Arc Cutting (AAC)Aircarbon-arccuttingisatypeofarccuttinginwhichthemetaliscutbymeltingwiththeheatofanarc,withuseofanairstreamtofacilitatecutting.Arc Gouging Arcgougingisana
106、pplicationofarccuttingusedtoproduceagrooveorbevelinthemetalsurface.Arc Welding and Cutting - ApplicationWhenarcwelding,eitheralternatingordirectcurrentisused.TheACandDClimitsshownbelowshallnotbeexceeded.ForACweldingunderwetconditionsorwarmsurroundingswhereperspirationisafactor,theuseofreliableautoma
107、ticcontrolsforreducingno-loadvoltageisrecommendedtoreducetheshockhazard.SomeoftheolderACmachinesdonothaveanautomaticcontrolandareonloadallthetime.Itiseasytoreceiveanelectricshockwhentheequipmentisnothandledproperly.AlternatingCurrent(AC)DirectCurrent(DC)Manual80Volts100VoltsAutomatic100Volts100Volts
108、Arc Welding and Cutting - InstallationArcweldingrequiresproperinstallationofequipment.Acriticalpartofinstallationisensuringthatpropergroundingiscompleted.Theframeorcaseoftheweldingmachine(exceptengine-drivenmachines)shallbegroundedundertheconditionsandaccordingtothemethodsprescribedinSubpartS,Electr
109、ical.Conduitscontainingelectricalconductorsshallnotbeusedforcompletingawork-leadcircuit.Pipelinesshallnotbeusedasapermanentpartofawork-leadcircuit,butmaybeusedduringconstruction,extension,orrepairprovidingcurrentisnotcarriedthroughthreadedjoints,flangedboltedjoints,orcaulkedjointsandthatspecialpreca
110、utionsareusedtoavoidsparkingatconnectionofthework-leadcable.Arc Welding and Cutting - Operation and MaintenanceBeforestartingoperations,allconnectionstothemachineshallbecheckedtomakecertainthattheyareproperlymade.Theworkleadshallbefirmlyattachedtothework.Magneticworkclampsshallbefreefromadherentmeta
111、lparticlesofspatteroncontactsurfaces.Coiledweldingcableshallbespreadoutbeforeusetoavoidseriousoverheatinganddamagetoinsulation.Duringweldingoperations,cableswithspliceswithin10feet(3m)oftheholdershallnotbeused.Weldersshouldnotcoilorloopweldingelectrodecablearoundpartsoftheirbody.Cableswithdamagedins
112、ulationorexposedbareconductorsshallbereplaced.Joininglengthsofworkandelectrodecablesshallbedonebytheuseofconnectingmeansspecificallyintendedforthatpurpose.Theconnectingmeansshallhaveinsulationadequatefortheserviceconditions.Resistance WeldingThethirdweldingprocesscoveredinthismoduleisresistanceweldi
113、ng.Resistanceweldingutilizespressureandheatthatisgeneratedinthepiecestobeweldedbyresistancetoanelectriccurrent.Whenconductingresistancewelding,allequipmentshallbeinstalledbyaqualifiedelectricianinconformancewithSubpartS,Electrical.Ifspotandseamweldingmachinesareused,thefollowingprecautionsmustbetake
114、n:lAlldoorsandaccesspanelsofallresistanceweldingmachinesandcontrolpanelsshallbekeptlockedandinterlockedtopreventaccesstoliveportionsoftheequipmentbyunauthorizedpersons.lInallpressweldingoperations,ifthereisapossibilityoftheoperatorsfingersbeingunderthepointofoperation,effectiveguardsmustbeused.Examp
115、lesofeffectiveguardsincludeanelectroniceyesafetycircuit,twohandcontrols,orprotectionsimilartothatprescribedforpunchpressoperations.Resistance WeldingThehazardofflyingsparksshallbe,whereverpractical,eliminatedbyinstallingashieldguardofsafetyglassorsuitablefire-resistantplasticatthepointofoperation.Ad
116、ditionalshieldsorcurtainsshallbeinstalledasnecessarytoprotectpassingpersonsfromflyingsparks.Allfootswitchesshallbeguardedtopreventaccidentaloperationofthemachine.Twoormoresafetyemergencystopbuttonsshallbeprovidedonallspecialmulti-spotweldingmachines,including2-postand4-postweldpresses.Additionally,allportableweldingguns,transformersandrelatedequipmentsuspendedfromoverheadstructures,eyebeams,trolleys,etc.,shallbeequippedwithsafetychainsorcables.Safetychainsorcablesshallbecapableofsupportingthetotalshockloadintheeventoffailureofanycomponentofthesupportingsystem.
