Txawm hais tias muaj kev tiv thaiv corrosion ntawm cov kav hlau stainless, cov kav hlau tsis muaj steel ntsia tau rau hauv marine ib puag ncig yog raug rau ntau hom kev xeb thaum lawv xav tau kev pab cuam lub neej.Qhov kev xeb no tuaj yeem ua rau muaj kev tawm tsam tawm, cov khoom lag luam poob thiab muaj peev xwm txaus ntshai.Offshore platform cov tswv thiab cov tswv lag luam tuaj yeem txo qhov kev pheej hmoo ntawm kev xeb los ntawm kev qhia cov khoom siv yeeb nkab uas muaj zog dua uas muab kev tiv thaiv corrosion zoo dua.Tom qab ntawd, lawv yuav tsum tau ceev faj thaum tshuaj xyuas cov kab tshuaj txhaj tshuaj, cov kab hydraulic thiab impulse, thiab cov txheej txheem kev ntsuas thiab ntsuas kom ntseeg tau tias kev xeb tsis cuam tshuam rau kev ncaj ncees ntawm cov kav dej los yog kev cuam tshuam kev nyab xeeb.
Localized corrosion tuaj yeem pom ntawm ntau lub platforms, nkoj, nkoj thiab cov kav dej tawm sab nraud.Qhov corrosion no tuaj yeem ua rau pitting lossis crevice corrosion, ob qho tib si tuaj yeem ua rau cov yeeb nkab phab ntsa thiab ua rau cov kua tso tawm.
Qhov kev pheej hmoo ntawm corrosion nce raws li kev khiav hauj lwm kub ntawm daim ntawv thov nce.Thaum tshav kub kub tuaj yeem ua kom lub cev degradation ntawm lub raj tiv thaiv sab nrauv passive oxide zaj duab xis, yog li txhawb pitting.
Hmoov tsis zoo, thaj chaw pitting thiab crevice corrosion yog qhov nyuaj rau kev kuaj xyuas, ua rau nws nyuaj rau txheeb xyuas, kwv yees, thiab tsim cov hom kev xeb.Muab cov kev pheej hmoo no, cov tswv platform, cov tswv lag luam thiab cov neeg tsim khoom yuav tsum tau ceev faj hauv kev xaiv cov khoom siv kav dej zoo tshaj plaws rau lawv daim ntawv thov.Kev xaiv cov khoom siv yog lawv thawj kab ntawm kev tiv thaiv corrosion, yog li kom tau txais nws txoj cai yog qhov tseem ceeb heev.Hmoov zoo, lawv tuaj yeem xaiv qhov yooj yim tab sis muaj txiaj ntsig zoo ntawm thaj chaw tiv thaiv corrosion, Pitting Resistance Equivalent Number (PREN).Qhov siab dua qhov PREN tus nqi ntawm cov hlau, qhov siab dua nws cov kev tiv thaiv rau hauv cheeb tsam corrosion.
Tsab ntawv xov xwm no yuav saib yuav ua li cas txheeb xyuas pitting thiab crevice corrosion, nrog rau yuav ua li cas txhawm rau txhim kho cov khoom siv tubing rau kev siv cov roj thiab cov roj offshore raws li cov khoom siv tus nqi PREN.
Localized corrosion tshwm sim nyob rau hauv cov cheeb tsam me me piv rau cov kev xeb dav dav, uas yog ntau yam sib xws ntawm cov hlau nto.Pitting thiab crevice corrosion pib ua rau ntawm 316 stainless hlau tubing thaum lub txheej chromium-nplua nuj passive oxide zaj duab xis ntawm cov hlau tawg vim raug cov kua dej corrosive, nrog rau cov dej ntsev.Marine ib puag ncig nplua nuj nyob rau hauv chlorides, nrog rau qhov kub thiab txias thiab txawm tias muaj kab mob ntawm cov tubing nto, ua rau kom muaj kev degradation ntawm no passivation zaj duab xis.
pitting Pitting corrosion tshwm sim thaum cov zaj duab xis passivation ntawm ib feem ntawm cov yeeb nkab tawg, tsim cov kab noj hniav me me los yog qhov pits ntawm qhov chaw ntawm cov yeeb nkab.Cov pits zoo li no yuav loj hlob raws li cov tshuaj electrochemical tshwm sim, vim tias cov hlau hauv cov hlau yog yaj hauv cov tshuaj hauv qab ntawm lub qhov.Cov hlau yaj tom qab ntawd yuav ya mus rau sab saum toj ntawm lub qhov thiab oxidize los ua hlau oxide los yog xeb.Raws li lub qhov tob tob, electrochemical kev cuam tshuam nrawm, corrosion tsub kom, uas tuaj yeem ua rau perforation ntawm cov yeeb nkab phab ntsa thiab ua rau xau.
Cov raj muaj qhov cuam tshuam rau pitting yog tias lawv qhov chaw sab nrauv muaj kab mob (Daim duab 1).Piv txwv li, cov kab mob sib kis los ntawm kev sib tsoo thiab kev sib tsoo tuaj yeem ua rau cov txheej txheem passivation oxide ntawm cov yeeb nkab, yog li tsim thiab nrawm pitting.Tib yam mus rau qhov tsuas yog cuam tshuam nrog cov pa phem los ntawm cov kav dej.Tsis tas li ntawd, raws li cov kua ntsev evaporate, cov kua ntsev ntub dej uas tsim rau ntawm cov kav dej tiv thaiv txheej oxide thiab tuaj yeem ua rau pitting.Txhawm rau tiv thaiv cov kab mob no, khaws koj cov kav dej kom huv los ntawm kev yaug lawv nrog dej tshiab.
Daim duab 1. 316/316L stainless hlau yeeb nkab uas muaj cov kua qaub, saline, thiab lwm yam deposits yog heev raug rau pitting.
corrosion kuj.Feem ntau, pitting tuaj yeem pom tau yooj yim los ntawm tus neeg teb xov tooj.Txawm li cas los xij, crevice corrosion tsis yooj yim los kuaj thiab ua rau muaj kev pheej hmoo ntau dua rau cov neeg ua haujlwm thiab cov neeg ua haujlwm.Qhov no feem ntau tshwm sim ntawm cov kav dej uas muaj qhov nqaim ntawm cov khoom nyob ib puag ncig, xws li cov kav dej tuav hauv qhov chaw nrog cov clamps lossis cov kav dej uas tau ntim nruj ntawm ib sab.Thaum cov brine nkag mus rau hauv qhov crevice, dhau sij hawm, cov tshuaj lom neeg aggressive acidified ferric chloride tov (FeCl3) yog tsim nyob rau hauv cheeb tsam no, uas ua rau crevice corrosion kom ceev (Daim duab 2).Txij li thaum crevice nws tus kheej ua rau muaj kev pheej hmoo ntawm corrosion, crevice corrosion tuaj yeem tshwm sim ntawm qhov kub thiab txias qis dua pitting.
Daim duab 2 - Crevice corrosion tuaj yeem tsim nruab nrab ntawm cov yeeb nkab thiab cov yeeb nkab txhawb nqa (sab saum toj) thiab thaum cov yeeb nkab tau teeb tsa ze rau lwm qhov chaw (hauv qab) vim yog kev tsim cov tshuaj lom neeg acidified tshuaj ntawm ferric chloride hauv qhov sib txawv.
Crevice corrosion feem ntau simulates pitting ua ntej nyob rau hauv qhov sib txawv ntawm cov yeeb nkab seem thiab cov yeeb nkab txhawb dab tshos.Txawm li cas los xij, vim qhov nce hauv qhov concentration ntawm Fe ++ hauv cov kua dej hauv cov pob txha, qhov pib funnel yuav loj dua thiab loj dua kom txog thaum nws npog tag nrho cov pob txha.Thaum kawg, crevice corrosion tuaj yeem ua rau perforation ntawm cov yeeb nkab.
Cov kab nrib pleb ntom ntom sawv cev qhov kev pheej hmoo loj tshaj plaws ntawm corrosion.Yog li ntawd, cov yeeb nkab clamps uas nyob ib puag ncig ib feem loj ntawm cov yeeb nkab qhov ncig yuav muaj kev pheej hmoo ntau dua li qhib clamps, uas txo qhov kev sib cuag ntawm cov yeeb nkab thiab clamp.Cov kws tshaj lij kev pabcuam tuaj yeem pab txo qis kev pheej hmoo ntawm crevice corrosion puas lossis tsis ua haujlwm los ntawm kev qhib clamps tsis tu ncua thiab xyuas cov yeeb nkab nto rau corrosion.
Pitting thiab crevice corrosion tuaj yeem tiv thaiv tau los ntawm kev xaiv cov hlau zoo rau daim ntawv thov.Cov neeg tshwj xeeb yuav tsum tau ua tib zoo saib xyuas hauv kev xaiv cov khoom siv zoo tshaj plaws los txo qhov kev pheej hmoo ntawm corrosion nyob ntawm tus txheej txheem ib puag ncig, txheej txheem txheej txheem, thiab lwm yam hloov pauv.
Txhawm rau pab cov kws tshaj lij txhim kho kev xaiv cov khoom siv, lawv tuaj yeem sib piv PREN qhov tseem ceeb ntawm cov hlau los txiav txim siab lawv cov kev tiv thaiv rau hauv zos corrosion.PREN tuaj yeem xam los ntawm cov khoom siv hlau, suav nrog nws cov chromium (Cr), molybdenum (Mo), thiab nitrogen (N) cov ntsiab lus, raws li hauv qab no:
PREN nce nrog cov ntsiab lus ntawm corrosion-resistant ntsiab ntawm chromium, molybdenum thiab nitrogen nyob rau hauv lub alloy.PREN piv yog raws li qhov tseem ceeb pitting kub (CPT) - qhov qis tshaj kub ntawm pitting tshwm sim - rau ntau yam stainless hlau nyob ntawm seb cov tshuaj muaj pes tsawg leeg.Qhov tseem ceeb, PREN yog proportional rau CPT.Yog li ntawd, ntau dua PREN qhov tseem ceeb qhia tau hais tias ntau dua pitting kuj.Ib qho kev nce me me hauv PREN tsuas yog sib npaug me me hauv CPT piv rau cov hlau, thaum qhov loj ntawm PREN qhia tau tias muaj kev txhim kho tseem ceeb hauv kev ua tau zoo tshaj qhov CPT siab dua.
Table 1 piv PREN qhov tseem ceeb rau ntau yam alloys feem ntau siv hauv kev lag luam offshore roj thiab roj.Nws qhia tau hais tias yuav ua li cas specification tuaj yeem txhim kho corrosion zoo los ntawm kev xaiv cov yeeb nkab zoo dua.PREN nce me ntsis ntawm 316 SS rau 317 SS.Super Austenitic 6 Mo SS lossis Super Duplex 2507 SS yog qhov zoo tagnrho rau kev nce qib hauv kev ua haujlwm.
Ntau nickel (Ni) concentrations nyob rau hauv stainless hlau kuj nce corrosion kuj.Txawm li cas los xij, cov ntsiab lus nickel ntawm stainless hlau tsis yog ib feem ntawm PREN kab zauv.Nyob rau hauv txhua rooj plaub, nws yog qhov zoo dua los xaiv cov hlau tsis muaj hlau nrog cov ntsiab lus nickel ntau dua, vim tias lub ntsiab lus no yuav pab rov ua dua qhov chaw uas pom cov cim ntawm qhov chaw corrosion.Nickel stabilizes austenite thiab tiv thaiv kev tsim martensite thaum khoov lossis kos duab txias 1/8 rigid yeeb nkab.Martensite yog ib qho tsis xav tau crystalline theem nyob rau hauv cov hlau uas txo qhov tsis kam ntawm cov hlau tsis muaj steel rau hauv zos corrosion nrog rau cov tshuaj chloride-induced kev ntxhov siab tawg.Cov ntsiab lus nickel ntau dua ntawm tsawg kawg yog 12% hauv 316/316L steel kuj yog qhov tsim nyog rau kev siv roj hydrogen siab.Qhov tsawg kawg nkaus nickel concentration xav tau rau ASTM 316/316L stainless hlau yog 10%.
Localized corrosion tuaj yeem tshwm sim nyob qhov twg ntawm cov kav dej siv nyob rau hauv marine ib puag ncig.Txawm li cas los xij, pitting feem ntau yuav tshwm sim nyob rau hauv cov cheeb tsam uas twb muaj kab mob, thaum crevice corrosion yuav tshwm sim nyob rau hauv cov cheeb tsam uas nqaim qhov sib txawv ntawm cov yeeb nkab thiab cov khoom siv installation.Siv PREN raws li lub hauv paus, tus specifier tuaj yeem xaiv cov yeeb nkab zoo tshaj plaws kom txo tau qhov kev pheej hmoo ntawm txhua yam hauv zos corrosion.
Txawm li cas los xij, nco ntsoov tias muaj lwm yam hloov pauv uas tuaj yeem cuam tshuam qhov kev pheej hmoo ntawm corrosion.Piv txwv li, qhov kub thiab txias cuam tshuam qhov tsis kam ntawm stainless hlau rau pitting.Rau cov huab cua hauv hiav txwv kub, super austenitic 6 molybdenum steel lossis super duplex 2507 stainless hlau kav yuav tsum tau txiav txim siab tiag tiag vim tias cov ntaub ntawv no muaj kev tiv thaiv zoo rau hauv cheeb tsam corrosion thiab chloride cracking.Rau cov huab cua txias, 316/316L yeeb nkab yuav txaus, tshwj xeeb tshaj yog muaj keeb kwm ntawm kev siv tau zoo.
Offshore platform cov tswv thiab cov tswv lag luam tseem tuaj yeem ua cov kauj ruam los txo qhov kev pheej hmoo ntawm corrosion tom qab tubing tau teeb tsa.Lawv yuav tsum khaws cov kav dej kom huv thiab tsis tu ncua nrog dej tshiab kom txo tau qhov kev pheej hmoo ntawm pitting.Lawv kuj yuav tsum muaj cov kws kho mob qhib cov yeeb nkab clamps thaum lub sij hawm niaj hnub tshuaj xyuas los xyuas qhov crevice corrosion.
Los ntawm kev ua raws li cov kauj ruam saum toj no, cov tswv platform thiab cov tswv lag luam tuaj yeem txo qhov kev pheej hmoo ntawm cov yeeb nkab corrosion thiab cuam tshuam txog kev xau hauv hiav txwv ib puag ncig, txhim kho kev nyab xeeb thiab kev ua haujlwm zoo, thiab txo qis cov khoom lag luam poob lossis kev tawm mus deb.
Brad Bollinger is the Oil and Gas Marketing Manager for Swagelok. He can be contacted at bradley.bollinger@swagelok.com.
Phau ntawv Journal of Petroleum Technology yog thawj phau ntawv xov xwm ntawm Lub Koom Haum ntawm Petroleum Engineers, muaj cov ntsiab lus tso cai thiab cov lus hais txog kev nce qib hauv kev siv thev naus laus zis, roj thiab roj teeb meem kev lag luam, thiab xov xwm txog SPE thiab nws cov tswv cuab.