Nominal Pipe Size and Schedule - The Process Piping

Nominal pipe size refers to only the outside diameter (OD) of a pipe making it somewhat vague. For example, when we say pipe size is 2 NPS, it ... Skiptocontent NominalPipeSize/PipeSchedule/PipingEnginnering NominalPipeSizeandSchedule by TheProcessPiping · PublishedJuly17,2018 ·UpdatedJuly10,2018 NominalPipeSize (NPS)isaNorthAmericansetofstandardsizesforpipesusedforhighorlowpressuresandtemperatures.Nominalpipesizereferstoonlytheoutsidediameter(OD)ofapipemakingitsomewhatvague.Forexample,whenwesaypipesizeis2NPS,itreferstoallthepipeshaving2.375-inch(or60.3 mm)asoutsidediameterirrespectiveofwallthicknessandthustheinsidediameter. Specificpipeisidentifiedbypipediameterandanothernon-dimensionalnumberforwallthicknessreferredtoastheSchedule(SCH).Pipeschedulesetsthepipewallthickness.Increasingthewallthicknessofthepipeincreasesthemechanicalstrengthofthepipe,allowingittohandlehigherdesignpressures. ThetermsNominalBore(NB) and NominalDiameter(DN)arealsofrequentlyusedinterchangeablywithNominalPipeSize(NPS). NominalBore(NB)isEuropeanDesignationequivalenttoNPS.ForNPS5andlarger,theNominalDiameter(DN)isequaltotheNPSmultipliedby 25. Initiallythereareonlythreepipewallthicknessesinuse– Standard(STD) ExtraStrong(XS) DoubleExtraStrong(XXS) Howeverwiththeadvancementofindustrialageanduseofpipesinvaryingpressureandtemperatureconditions,thesethreesizesdidnotfitallapplications.Therehavebeenmanyrevisionsandadditionstothetablesofpipesizesbasedonindustryuseandonstandardsfrom API, ASTM,andothers.Todaywehavearangeofwallthicknesses,namely: SCH5,5S,10,10S,20,30,40,40S,60,80,80S,100,120,140,160,STD,XSANDXXS. Stainlesssteelpipes,duetolessriskoffailureduetonon-corrosiveproperty,permittedtheuseofpipeswiththinnerwallthickness.Initiallythinnerpipeschedules5Sand10Shadbeencreatedandafterwardsother“S”sizesfollowedlater.Stainlesssteelpipesaremostoftenavailableinstandardweightsizes(notedbythe S designation;forexample, Sch10S).Howeverstainlesssteelpipecanalsobeavailableinotherschedules.Duetotheirthinwalls,thesmaller“S”sizescannotbethreadedtogetheraccordingtoASMEcode,butmustbe fusionwelded. Innewschedulesystem, ScheduleStandard(STD)isidenticaltoSCH40S,and40Sisidenticalto40forNPS1/8toNPS10,inclusive. ScheduleExtraStrong(XS)isidenticaltoSCH80S,and80Sisidenticalto80forNPS1/8toNPS8,inclusive. ScheduleDoubleExtraStrong(XXS)wallisthickerthanschedule160fromNPS1/8 intoNPS6 ininclusive,andschedule160isthickerthanXXSwallforNPS8 inandlarger. NominalPipeSizeandSchedulecollectively setsthepipeoutsidediameter(OD)andthewallthickness(andhencetheinternaldiameter(ID)isautomaticallyfixed). Forexample,NPS14Sch40hasanODof14inches(360 mm)andawallthicknessof0.437inches(11.1 mm). HowevertheNominalPipeSize(NPS)andOutsideDiameter(OD)valuesarenotalwaysequal,whichcancreateconfusion. ForNPS⅛to12–TheNPSandODvaluesaredifferent.Forexample,theODofanNPS12pipeisactually12.75inches(324 mm).TofindtheactualODforeachNPSvalue,refertothereferencetableswhicharebasedonASMEstandardsB36.10MandB36.19M. ForNPS14andabove– TheNPSandODvaluesareequal.Inotherwords,anNPS14pipeisactually14inches(360 mm)OD. Fewgeneralrulesregardingnominalpipesize(NPS)andschedule, ForagivenNPS,theODstaysfixedandthewallthicknessincreaseswithincreaseinschedulenumber. Foragivenschedulenumber,theODincreaseswithNPSwhilethewallthicknesseitherstaysconstantorincreases. UsingequationsandrulesinASMEB31.3ProcessPiping,itcanbeshownthatpressureratingdecreaseswithincreasingNPSandconstantschedule. CalculationofPipeInternalDiameter(ID) Forprocessengineers,themostimportantinformationisthepipeInternalDiameter(ID),asthisisusedin linesizingcalculations.Asdiscussedabove,foragivenNominalPipeSize(NPS),thepipeOutsideDiameter(OD)remainsconstant.Asthepipeschedulechanges,theIDofthepipechanges. TheIDofthepipecanbeeasilycalculated,aslongasthepipeNPSandscheduleareknown.ThepipeIDisgiven bythepipeNPSminusdoublethepipewallthickness(whichcanbeobtainedfromthepipeschedule). Forexample,fora12NPS(DN300mm)pipe,schedule40,theODandwallthicknessarerespectively 12.75inches(324mm)and0.406inches(10.4mm).Thus: PipeID=12.75inches–2x0.406inches=11.94inches,or PipeID=324mm–2x10.4mm=303.2mm. Itisworthbearinginmindthatwallthicknessescomewithinaspecifiedtolerance,dependingon theengineeringstandardused.Atypicalwallthicknesstoleranceis12.5%.Thismeansthattheactual internalpipediametermayvaryslightlyfromthatquotedabove. NominalPipeSizeandPipeScheduleChart (DownloadPDFFile)   TheProcessPipingatechnicalknowledgebaseforalltheprocesspipingprofessionalsaroundtheworld… Share Tags:nominalborenominaldiameternominalpipesizeschedule TheProcessPiping atechnicalknowledgebaseforalltheprocesspipingprofessionalsaroundtheworld... 2Responses Comments2 Pingbacks0 CharlesDiestelsays: July21,2018at10:48AM Verygoodtothepointarticle. zohabsays: July17,2018at4:23PM Goodjobteamprocesspiping. However,thereisaclericalerrorinthearticleitseems. ForNPS5andlarger,theNominalDiameter(DN)isequaltotheNPSmultipliedby25. ThisstatementinthearticleshouldbeForNPS4andlarger.TheNominalDiameterequalstoNPS*25.Shouldn’tit? 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