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Wear Resistance of CO2 Corrosion Product Scale Formed at High Temperature

By Martin Richardson,2014-08-06 12:22
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Wear Resistance of CO2 Corrosion Product Scale Formed at High Temperatureof,at,CO2,Scale,High,Wear,scale,high

    Wear Resistance of CO2 Corrosion Product

    Scale Formed at High Temperature AvailableonlineatWWW.sciencedirect.com

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    JOURNMOFIRONANDSTEELRESEARCH,INTERNATIONAL.2006,13(5):4752

    WearResistanceofCO2CorrosionProductScale

    LINGuanfa.

    FormedatHighTemperature

    ZHENGMaosheng,BAIZhenquan,FENGYaorong

    (1.KeyLaboratoryforMechanicalandEnvironmentalBehaviorofTubularGoods,ChinaNational

    PetroleumCorporation,Xian710065,Shaanxi,China;2.SchoolofMaterialScienceand Engineering,XianJiaotongUniversity,Xian710049,Shaanxi,China)

    Abstract:rr0investigatethecorrelationbetweenstructurecharacteristicsandwearresistanceofC02corrosionproduct

    scalesathightemperatureandhighpressure,anautoclavewasusedtoprepareCO2corrosionproductscalesonNS0

    stee1incarbondioxidecorrosionenvironment.Thecorrelationbetweenwearresistanceofthescalesandmanyother

    factors,suchastemperature,pressure,morphology,structure,velocityoffluidmedium,sandgrainsize,andso

    on,wascomparativelyanalyzedbyaselfassembledweardevice,andthescalemorphologiesbeforeorafterbeing

    wornwereobservedbyscanningelectronmicroscope(SEM).Andthenthesurfacegrainsizeandthicknessofscale

    weremeasured.Theresultsshowedthatthecross

sectionofthecorrosionscalewasofadouble-layerstructure,the

    outerlayerofwhichwascomposedofregularcrystals,whereastheinnerlayerwasathinscaleoffinegrains.The

    outergrainsizeandthicknessofscalevariedwithtemperature,andtheinitia1wear1OSSwasconsistentwiththesur

    facegrainsize;atthesametime,thetota1wear1OSScorrespondedtothethicknessofscale.Comparedtowearresist

    anceindifferentdepthsofthescale,itwasfoundthatthestructureofscalewasadouble-layerstructureincrosssee

    tion,andthewearresistanceofinnerlayerwasbetterthanthatoftheouter1ayer;thecloserthescaletothematrix.

    thegreaterwasthewearresistanceofscale;andthelargerthesizeorthehighertherotaryspeedofsolidgrainin

    muhiphaseflowingmedium,themorewasthewear1OSSofscale.

    Keywords:C()2corrosion;corrosionproductscale;wear;NS0stee1;morphology;structure CO7corrosionoccurswidelyinpetroleumindus

    try,andespeciallyinboththecomponentsofoilex

    tractionandpipelinestransportingoil,whichresul

    tedina1argeamountofeconomic1ossesandcalami

    ties.SotheresearchonCO7corrosionandpreven

    tionisveryimportant.Alotofresearchesindicated

    thatCO2corrosionproductscaleformedoncarbon

    steelsurfaceinC0,corrosionmediumE3.andthis

    scaleeffectivelydecreasedthecorrosionrateofthe

    matrix.Whileundertheactualserviceconditions,

    theservicecomponentssufferedfromtheerosion

    andwearbehaviorsofflowmediumcommixedwith

    solidparticlesimpurity,andtheerosionandwear

    increasedthecorrosionofmaterialsE3.Whenthe

    corrosionmediumcontainedalittleofsolidparticles

    and/oritwasatalowrotaryspeed,thecorrosion productscaleformedonthematerialssurfaceandin awayitprotectedthematrixfromcorrosion.The corrosionrateofthematrixdependsonthephysical characteristicsofthecorrosionproductscales.some ofwhicharethemaininfluencingfactors,suchas thescaleformationcondition,morphologycharac

    teristics,hierarchystructure,chemicalcomposition ofthecorrosionscales,andsoon.Toinvestigate thecorrelationbetweenthestructurecharacteristics andwearresistanceofCO2corrosionproductathigh temperatureandhighpressure,anautoclavewas usedtoprepareCO2corrosionproductscalesonN80 FoundationItem:ltemSponsoredbyNationalNaturalScienceFoundationofChina(502310

    20),NationalBasicResearchProgramofChina (G1999065004),2001KeyLaboratoryOpeningFundofCorrosionandProtectionofTabular

    GoodsResearchCenterofChina

    NationalPetroleumCorporation(ZYT01070)

    Biography:I.INGuan-fa(1960

    ),Male,Doctor,AssociateProfessor;E-mail:lingfS08@126.com;RevisedDate:March3

    ,2006

?

    48?JournalofIronandSteelResearch,International steelincarbondioxidecorrosionenvironment;the wearresistanceofthescalesformedunderdifferent conditionsweremeasured;andthevariationoftheir wearpropertieswithhierarchicalstructures,mor

    phologycharacteristics,andconditionsthatformed

corrosionscaleswasinvestigatedbyaselfassembled

    weardeviceinmuhiphasefluidmediumunderdry wearcondition.Themicrostructureandmorphology characteristicsofscalesbeforeorafterbeingworn wereobservedwithSEM,andthesurfacegrainsize andthicknessofscaleswerealsomeasuredwith SEM.

    1ExperimentalMethod

    1-1PreparationofC02corrosionproductscales ThechemicalcompositionofN80welltubing steelis(masspercent,):CO.2O,SiO.2O,Mn 1.34,PO.O18,S0.007,Cr0.050,Mo0.014,Ni 0.029,V0.007,Ti0.024,andCu0.01.Thesteel samplesweremachinedintoslicesof30.0mm×

    26.0mm×1.8mm,andpolishedwithSiCpapers

    from12Oto1000.Acetonewasusedtoremove theoilfromthesamplessurfaces.Thesimulated oilfieldextractedoilliquidwasadoptedasthetes

    tingmedium.Theionconcentrations(g/L)areas follows:C119.0,So1.14,HCO~-0.6,Mg

    1.O5,Ca0.39,Na1.l1.99,Co;0.12,andpH

    value6.0.

    Theexperimentwasperformedina34.44M.Pa staticautoclavemanufacturedbyCortestCo(America). Agroupofninesteelsampleswasplacedintheauto

    clave;afterwardthecorrosivemediumwaspouredinto theautoclave.Afterbeingsealedandcovered,ni- trogengaswasaeratedtodriveoxygengasfor6h, andthenCO,wasaeratedfor8h.Invaryingtem

    peratureexperiments,theCO2partialpressurewas

keptwithin1.392.75MPa.Theexperimentalpe

    riodwas4d.Aftertheexperiments,thecorrosion sampleswerewashedwithwater,anddriedwithab- solutealcoho1.Finally,thesampleswerekeptinthe otherdesiccatorsforfurtheruse.

    1.2Weartestsofscales

    Thewearexperimentswerecarriedoutinwa

    ter——sanddouble——phasemediumusingaself——assem——

    bledweardevice[atroomtemperature.Themedi

    umwascommixedwithwaterandsandbythe

    weightratioof2:1.Thesamplesofweartests weremachinedintoslicesof30.0mm×8.0mm×

    1.8mm.Thesampleswereweightedwithanelec

    Vo1.13

    tronbalancewithsensitivityof0.1mgbeforebeing worn,andthenthesampleswereaffixedonthein

    nersurfaceoftheweardevicewithasiliconrubber NQ704.Afterthesamplesweresolidified.thewear mediumwasaddedtothedeviceandwasrotated. Aftereachexperiment,thesampleswerewashed withwater,driedwithalcohol,weighted,andfinal

    lyputintothedesiccatorsforthenextexperiment. Thewearingtestsateachrotaryspeedweredonefor severaltimes,andthesampleswerewornfor1heach time:theinitialandfinalrotaryspeedsweremeas

    uredwithalaserspeedometer.Thewearexperi

    mentswerefirstcarriedoutatlowerrotaryspeed, andthentherotaryspeedwasraisedstepbystepaf

    terthewearlOSSwasnotapparent.Whenthewhole ofthescalewaswornoffandthesurfaceofmatrix

    wasexposed,thewearexperimentswereover.The wearlOSSatfirstrotaryspeediscalled"initialwear lOSS",andthewholewearlOSSofthescaleiscalled "totalwearlOSS".

    Themorphologyofthesurface,crosssection,

    andwearsurfaceofthecorrosionproductscalewere observedwithanSEM,PhilipsXL-20,andthe scanningconditionsweremarkedoutintheirfig

    ures;thesurfacegrainsizeandthicknessofthescale weremeasuredwiththedividingruleroftheSEM. 2ResultsandDiscussion

    2.1Morphologycharacteristicsofcorrosionscale Throughdirectobservation,itcanbefound thatapucethinscalecomposingmainlyofFeCO3,a littleofCaCO3,Fe,andFe3Cismacroscopically formedoneachsampleaftercorrosion.TheCa comesfromthecorrosionmedium,whilealittleof bothFeandFe3Ccomesfromthematrixencapsula

    tedinthescaleL.Theouterlayerappearsasinter

    crossedregularrhombohedralcrystalsthroughSEM observation,andthegrainsizesvarywiththetem

    perature,asshowninFig.1(a)and(b).Whenthe crosssectionscalewasobserved,thecorrosionscale showsdoublelayerstructure,andtheouterlayeris ofregulargrainstructure;thesectionbetweenouter layerandmetalmatrixisathinlayer(consideredas theinnerlayer),asshowninFig.1(c).Thesur

    facecharacteristicsandhiberarchyofthecorrosion scalesareconnectedwiththeirformingmechanism andcondition.Inthebeginningofthecorrosion

    process,becausethereisnoFeinthemedium,a littleCaCOcanbeformedonthematrixsurface first.butitcannotpreventthetransmissionofcorrosion

No.5WearResistanceofCO2CorrosionProductScaleFormedatHighTemperature?49?

    (a)120C,0.62MPa;(b)90?,10.34MPa;(c)100?.0.69MPa

    Fig.1SEMimagesofsurfaceandlongitudinalcharacteristicsofN80corrosionscale

    medium.Withthecorrosionproceeding,theFe

    concentratesinthemediumquicklyandfinallyex

    ceedsthesaturatedconcentrationofFeCO,and thensmal1grainsbegintodepositonthematrixsur

    face.Asthescalelayerincreasing,thecorrosion ratedecreasessharplytil1relativestabilizationis reached,andthegrainsmainlydepositonthesur

    faceofthescaleformedpreviously.Atthefina1 step,whentheconcentrationofFeis1owandap

    proachestothesaturationconcentration,theformed grainsareregularinstructureandlargeinsize.The smal1grainsdissolve,andatthesametime,the1ar

    gergrainsgrowup,andthegrainsizeintheendofcor

    rosiondependsonthecontrolledconditionofthecorro

    sionprocess(suchastemperature,CO2pressure,etc.). Sothedoublelayerstructurewasformed,wherethe grainsoftheouter1ayerarecoarse,whereasthose oftheinner1ayerarefine.

    Theresultsofwearexperimentsshowthatthe morphologyofthewornscalebeforeandafterthe interfaceshowsobviousdifferences.Comparatively, asshowninFig.2,thereareholesformedfrom 1argegrainsinorigina1surfaceofthecorrosionscale

    EseeFig.1(a)],andtheoriginalsurfaceofthescale turnsintoeveneroneafterbeingwornfor5h,the grainsizedecreasesandthesurfaceofthescaleis moreevenEseeFig.2(a)].Withtheincreaseofthe rotaryspeedandthewearingtime,thewornsurface ofthescalebecomeseven,andthecoarsegrainsand holesoftheouterlayerdisappeargradually[see Fig.2(b)].Atthesametime,itcanbeseenfrom Fig.2(b)and(c)thatwiththeincreaseoftherota

    ryspeedornearthematrix,fuscousdistrictsofthe scaledecreasegraduallyandbrightdistrictsincrease largerandlarger.Throughenergydispersionanaly

    zerofXray(EDAX),itisfoundthatthebrightdis

    trictscontainmainlyFeandFe3C,whilethefuscous districtsincludebasicallythecorrosionproduct scale,whichresultsfromanuneveninterfaceformed betweentheinnerlayerofscaleandthematrixsur

    faceinthecorrosionprocess,andthereasonisthat therearepittingcorrosionsintheformationofthe corrosionscale.

    2.2Effectoftemperatureonmorphologycharacter- isticsofcorrosionscale

    Whenthetesttemperatureis1owerthan60?.

    thecorrosionscalecomposingmainlyofFeCOaissoft andfreeofadhesionforce,andthesurfaceofthema

    trixiSsmooth,whichisuniformcorrosion.Sothe experimenttemperatureatthebeginningis80?.

    Fig.3showsthevariationofsurfacegrainsizeand thicknessofcorrosionscalewiththeformingtem

    peraturefortheN80stee1.Itcanbeseenthatthe

    surfacegrainsizesincreasefirstwiththetemperature, thendecrease,andfinallyincreaseagain.Therearea Formingconditionofscale:180?,1.21MPa

    (a)300330r/rain,05h;(b)400440r/rain,520h;(c)650710r/rain.2937h

    Fig?2Morphologycharacteristicsofcorrosionscaleatcontinualdifferentrotaryspeeds

    ?5O?JournalofIronandSteelResearch,International 25

    15

    10

    120160200

    Temperature/?

    Fig.3Variationofsurfacegrainsize(a)and scalethickness(b)withtemperature

    maximumvalueandaminimumvalueofgrainsizes atthetemperatures120.Cand160?.respectively.A

    maximumvalueandaminimumvalueofthescalethick

    nessappearalsosimilarlyattemperatures120?and

    160?,respectively.Atthetemperaturethatthe minimumvaluesofthethicknessandgrainsizeap

    pear,theC02corrosionscaleisthetightest,the tightscalehashighadhesiveforcewiththematrix, andthetemperatureisconsistentwiththatofthe minimumcorrosionrateofcarbonsteelsinCO,cor

    rosionmediumasreportedbymanyliteratures.As thethicknessofthecorrosionscaleistheminimum andthecorrespondingcorrosionrateisalsothemin

    imumatthistemperature,thescaleisgoodforCO2 corrosionresistance,andespecially,thesmallgrains

intheinnerlayerplayanimportantroleinprohibi

    tingthetransmissionofthecorrosionmediumtothe matrixsurface.

    Generally,thethicknessofCO2corrosionscale onthematrixisconsistentwiththeaveragecorro

    sionrate,andthesurfacegrainsizesdependonthe mediumtemperature,concentrationanddissolvabili

    tyofthesoluteatthefinalcorrosionstep.Inthe CO2corrosionprocessofN80steelcoveredbycorro

    sionproductscale,theaveragecorrosionrateisre

    latedmainlywiththetightnessofcorrosionscale Vol_13

    (especiallytheinnerscale).Atlowercorrosiontern perature,theinitialcorrosionrateislower,butas thetightnessofcorrosionscaleisbad,thecorrosion ratedecreasesalittle.thustheaveragecorrosion rateishigher;whileathighertemperature,theini

    tialcorrosionrateishigher.butasthecorrosionscale isofbettertightness,thecorrosionratedecreases sharply,sotheaveragecorrosionrateislower. Accordingtocrystalchemicaltheory,whenthe crystallizingprocesshaspositivetemperatureeffect, thehigherthetemperature,thegreaterthedissolva

    bility,andthelowerthesuDersaturatedconcentra

    tion,whichishelpfulinforminglargergrainsolute. AsthetemperatureeffectofthedissolvabilityofFe

    CO3isnegative,itscrystallizingprocessismore complex.Consideringtheeffectoftemperatureand dissolvabilityinFeCO3crystallizingprocess,the

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