Boiler Grade DMV 310 N

DMV 310 NDMV 310 N

1 Introduction ___________________________________________________________________4 1.1 Salzgitter Mannesmann Stainless Tubes ________________________________________4 1.2 DMV 310 N _________________________________________________________________5 1.3 Trend ______________________________________________________________________5 1.4 Specifications(Standards) ____________________________________________________6 1.5 Available Sizes ______________________________________________________________6 1.6 Special Features _____________________________________________________________6

2 Material Properties _____________________________________________________________8 2.1 Microstructure ______________________________________________________________8 2.2 MaterialpropertiesaccordingtoASME _________________________________________9 2.2.1 Chemicalcomposition ___________________________________________________9 2.2.2 Mechanicalproperties _________________________________________________ 10 2.3 MaterialpropertiesaccordingtoVdTV ______________________________________ 12 2.3.1 Chemicalcomposition _________________________________________________ 12 2.3.2 Tensileproperties ______________________________________________________ 12 2.3.3 Creep strength ________________________________________________________ 14 2.3.4 Impact resistance _____________________________________________________ 15 2.3.5 Physicalproperties ____________________________________________________ 15 2.4 HightemperaturepropertiesMechanism ____________________________________ 17 2.4.1 High temperature and creep rupture strength _____________________________ 17 2.4.2 Microstructurestability _________________________________________________ 18 2.5 Corrosionresistance _______________________________________________________ 19

3 Fabrication __________________________________________________________________ 20 3.1 Tube bending _____________________________________________________________ 20 3.2 Welding __________________________________________________________________ 20

4 References __________________________________________________________________ 22

Content

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1.1 Salzgitter Mannesmann Stainless TubesSalzgitter Mannesmann Stainless Tubes is oneoftheleadingmanufacturersofseam-lessstainlesssteelandnickelalloytubesandpipes.Ourcompanyhasoneofthelarg-estproductportfoliosinthissector.Ourtopqualityproductsandefficientservicecontributetothelong-termsuccessofourcustomers.Ourtoppriorityistoestablishandmaintainpositivelong-termrelationshipswithourbusinesspartners.Inordertosupportyouinthestockistandprojectbusiness,withgoodquality,innova-tivematerialsandmodernproductiontech-nologies,ourexpertsareconstantlyworking

tokeepupwiththelatesttrends.Asacompanyoperatingsuccessfullyonaninternationallevel,weunitemanynation-alitiesandculturesunderonebanner.Ournetworkcollaboratescloselyinallaspectsofprocurement,sales,productionandlogistics.Sinceourfoundationasajointventure,weholdourpositioninthetopleagueofcompa-niesinthissector.WeareamemberofthepowerfulSalzgit-terGroupandourstainlesssteelandnickelbaseproductsareanimportantadditiontotheGroupsoverallproductrange.Thankstoourimpressiveproductportfolio,wecanopenupattractivegrowthprospects.

1 Introduction

Headquarters Mlheim an der Ruhr, Germany

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1.2 DMV 310 NOurtubesandpipesareprimarilyusedforboilersinthermalpowerplantsandtheenergysector.Thetrendistowardshighersteamtemperaturestoincreasetheefficien-cyofpowerplantsontheonehandandtheuseofhighchlorineandsulphurcontainingcoalontheotherhand.Conventional18-8stainless steels such as grades 304 and 347 donotshowsufficientcorrosionresistanceinthesecases.ThehigherCrcontainingstainlesssteelsoftype310(25Cr-20Ni)ex-hibitahighercorrosionresistance.Thistypehasbeenconsideredasacandidatematerialincaseswherehighercorrosionresistanceisrequiredandthehighermaterialcostsareacceptable.However,thecreeprupturestrengthofconventional310stainlesssteelisratherlow.Thus,thesesteelscannotbeusedtoproducesuperheatertubesutilisedabove600C(1110F).Tofindaremedy,compositetubeshavebeenproducedcladwithtype310stainlesssteelasthefire-sidecomponentonacoresteeltubewhichpro-videssatisfactorycreepresistance.WithDMV310N,thedisadvantageoflowstrengthandcreepresistanceisovercome,whileretainingthehighcorrosionresistance.Theadditionofniobiumandnitrogenresultsin increased elevated temperature strength andcreepresistance.Theeffectsofsolidsolutionstrengtheningbynitrogentogetherwiththeprecipitationhardeningbyfineandstable NbCrN are used. 310 stainless steels canbepronetotheformationofcoarse

secondaryphasessuchassigmaphaseandCr2Nresultinginanembrittlementofthema-terial(reducedtoughness).Anoptimisationofthecomposition(mainlynickel,niobiumandnitrogencontent)wasnecessarytoin-creasethemicrostructuralstability.Thereforethealloycompositionisdesignedtofindtheoptimumbalancebetweenthevariousproperties.Inthisway,tubinginDMV310Nisnowsuitableforuseinsuperheaterboilersabove600C(1110F).

1.3 Trend Efficiencyisamajorperformancecriterionforpowerplantsandboilers.Increasingef-ficiencyessentiallyresultsinareductionofthefuelconsumptionandthusCO2emis-sions,whichisabigchallengeatthepresenttime.Higherefficiencyofsuchequipmentis reached by higher steam temperatures andpressures.Targetserviceconditionsarecurrentlysteamtemperaturesabove600Cor1110Fandpressuresofmorethan300baror4,350psi.Thematerialsmustwith-standtheseconditionsthroughoutthewholeservicelifeofthecomponent.Thisresultsinhigherdemandsoncreepresistance,elevated temperature strength and high temperaturecorrosionresistance.Theuseofcoalwithahighchlorineandsulphurcontentfurtherincreasestheneedforfire-sidecor-rosionresistance.ThesechallengesaremetbyDMV310N,inwhichthehighcorrosionresistanceoftype310materialsiscombinedwith increased high temperature strength

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and creep resistance. Infuture,steeldevelopmentmustcontinuetofollowthenewdemandsandchallengesofboilerapplications.Itiswidelyexpectedthatnewpowerplantswillrunatevenhighertemperatures and pressures. Nickel based alloysinparticularwillbeabletomeetfuturerequirements,suchasDMV617(fordesigntemperatures>700C).However,theseal-loyshavehighnickelandchromiumcontentandarethusmoreexpensive.

1.4 Specifications (Standards)DMV310Nfulfilstherequirementsaccord-ingtothefollowingspecifications: 1.4952(X6CrNiNbN2520),accordingtoEN10216-5,EuropeanStandard

TP310HCbN(25Cr-20Ni-Nb-N)accordingtoASMESA-213,USStandard

ASMECodeCase2115-1(02.2000),UnitedStates

VdTVmaterialdatasheet546(03.2007),FederalRepublicofGermany

1.5 Available SizesDMV 310 N austenitic stainless steel is used tomanufactureseamlessausteniticreheaterandsuperheaterboilertubes.Thisgradeissuitableforallcommonlyusedausteniticreheaterandsuperheaterboilertubesizesinthemostadvancedcoalfiredpowerstationswithsteamtemperaturesupto620C (1150F)andsupercriticalorultrasupercriti-

calboilerdesign.VdTVmaterialdatasheet546(03.2007)allowsamaximumouterdiameterof65mmandamaximumwallthicknessof12.5mm.ThestandardsizerangeaccordingtoEN-ISO1127aswellasothersizesarealsoavailableuponrequest.

1.6 Special Features DMV310Nisanoptimisedausteniticstainlesssteeloftype310,suitableforuseas tubes in severe conditionsofmodernboilers(e.g.ultrasupercriticalboilers)withanappropriatecombinationofhighcorro-sionresistanceandhighelevatedtempera-ture strength.

Production route of DMV 310 N: The materialisfirstsubjectedtoahotformingprocess(hotextrusion).Subsequently,coldfinishingiscarriedoutonthematerial,fol-lowedbysolutionannealingatatempera-turebetween1180Cand1270C (2155Fand2320F)accordingtoVdTVdatasheet546(03.2007).

Ahighfire-sidehotcorrosion resistance andsteam-sideoxidationresistanceisen-suredbyahighchromiumcontentof25%.

Satisfactoryelevated temperature strength and creep resistance is achievedbythecontrolledadditionsofnitrogenandniobium:solidsolutionstrengtheningandprecipitationhardeningareemployed.

1 Introduction

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TheoptimisedcompositionofDMV310N results in a microstructural stability reducingthetendencytowardsformationofcoarsesigmaandCr2Nphase,andthusreducingembrittlementofthematerial.

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2.1 MicrostructureThe material DMV 310 N is a type 310 austeniticstainlesssteelwithhighcorrosionresistance.Improvementsintheelevatedtemperature strength and creep resistance comparedtotheconventional310typesare mainly achieved by a balanced addi-tionofniobiumandnitrogen.Inparticularthenitrogencontentisincreasedcomparedtothe310typeausteniticsteelsaswellascomparedtootherboilertubegradessuchasDMV347HFGandDMV304HCu.Toincreasethestrengthofthematerial,primar-ilytheeffectofsolidsolution-strengtheningbynitrogenisused.Thecreepresistanceisfurtherincreasedduringservicebythefineprecipitationofcarbonitrides,Zphase(com-plexnitride)andM23C6 carbides. Neverthe-less,ahighamountofnitrogenremainsinsolutionintheausteniticmatrix[1]. Theproductionofboilertubesisdividedintothreemainprocessingsteps.Afirstthermaltreatmentisperformedduringthehotextru-sionofthematerial.Thisisfollowedbycolddeformationtoproducethefinaldimensionsofthetube(coldpilgeringorcolddrawing).Afinalheattreatmentcompletestheproduc-tionroute.Duringthissolutiontreatment,theprecipitatesaremainlydissolvedintheausteniticmatrix.Ahighsolutionrateisnecessarytoachievegoodcreepproperties.However,acertainamountofprecipitatesremains,restrictingthegraincoarseningbypinningthegrainboundaries.Thesetwoaims are achieved by using a thermal treat-

mentwhichisoptimisedintemperatureandtime.ThemicrostructureofDMV310Ninas-deliveredconditionisshowninFigure1.

Inthesolution-annealedconditionthedis-solvednitrogenincreasesthetensilestrengthatroomtemperatureandelevatedtempera-turesbythesolidsolution-strengtheningeffect.Undercreepconditionsinservice,precipitationofdifferentphasesbegins.Aswellasthewell-knownphasessuchasniobiumcarbonitr