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 muaj ntau hom kev xeb thaum lawv lub neej xav tau.Qhov corrosion tuaj yeem ua rau cov pa phem, cov khoom poob thiab muaj peev xwm txaus ntshai.Offshore platform cov tswv thiab cov tswv lag luam tuaj yeem txo qhov kev pheej hmoo ntawm corrosion los ntawm kev qhia cov yeeb nkab muaj zog cov ntaub ntawv uas muab kev tiv thaiv corrosion zoo dua. Cov cuab yeej ntsuas ntsuas kom ntseeg tau tias kev xeb tsis cuam tshuam rau kev ncaj ncees ntawm cov kav dej txuas thiab cuam tshuam kev nyab xeeb.
Localized corrosion tuaj yeem pom ntawm ntau lub platforms, cov nkoj, nkoj, thiab cov kav dej hauv cov khoom siv sab nrauv.Qhov corrosion 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 dej tso tawm.
Qhov kev pheej hmoo ntawm corrosion yog ntau dua thaum qhov kev khiav hauj lwm kub ntawm daim ntawv thov tsub kom.Heat tuaj yeem ua kom puas tsuaj ntawm kev tiv thaiv sab nrauv passive oxide zaj duab xis ntawm lub raj, yog li txhawb kev tsim pitting corrosion.
Hmoov tsis zoo, thaj chaw pitting thiab crevice corrosion tsis yooj yim rau kev txheeb xyuas, ua rau cov hom corrosion nyuaj dua los txheeb xyuas, kwv yees thiab tsim qauv rau.Muab cov kev pheej hmoo no, cov tswv platform, cov tswv lag luam thiab cov neeg tsim qauv yuav tsum tau ceev faj thaum xaiv cov kav dej zoo tshaj plaws rau lawv daim ntawv thov.Cov khoom xaiv yog lawv thawj kab ntawm kev tiv thaiv corrosion, yog li tau txais nws txoj cai yog ib qho tseem ceeb heev.Ua tsaug rau kev siv cov tshuaj tiv thaiv hauv zos, hmoov zoo heev. Resistance Equivalent Number (PREN).Qhov siab dua qhov PREN tus nqi ntawm cov hlau, qhov siab dua nws cov kev tiv thaiv hauv cheeb tsam corrosion.
Kab lus no yuav tshuaj xyuas yuav ua li cas txheeb xyuas pitting thiab crevice corrosion thiab 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 kev xeb, uas yog ntau yam ntawm cov hlau nto.Pitting thiab crevice corrosion pib tsim ntawm 316 stainless hlau kav thaum hlau cov txheej chromium-nplua nuj passive oxide zaj duab xis ruptures vim raug corrosive kua, nrog rau cov ntsev dej.Chloride-nplua nuj offshore thiab onshore marine ib puag ncig, thiab txawm tias muaj peev xwm ua rau muaj kev kub nyhiab ntawm ntug dej hiav txwv. degradation ntawm no passivation zaj duab xis.
pitting.Pitting corrosion tshwm sim thaum cov yeeb yaj kiab passivation ntawm qhov ntev ntawm cov yeeb nkab raug rhuav tshem, 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, ua rau cov hlau hauv cov hlau yaj mus rau hauv cov tshuaj hauv qab ntawm lub qhov dej. Cov hlau yaj yuav tom qab ntawd diffuse mus rau sab saum toj ntawm lub qhov dej thiab oxidize cov tshuaj tiv thaiv oxides. nrawm, corrosion intensifies, thiab tuaj yeem ua rau perforation ntawm cov yeeb nkab phab ntsa thiab ua rau cov xau.
Tubing yog qhov yooj yim rau pitting corrosion thaum nws sab nrauv yog paug (Daim duab 1). Piv txwv li, kev sib kis ntawm vuam thiab kev sib tsoo ua haujlwm tuaj yeem ua rau cov txheej txheem oxide passivating ntawm cov yeeb nkab, yog li tsim thiab nrawm pitting corrosion.Tib yam mus rau qhov yooj yim cuam tshuam nrog kev sib kis los ntawm cov kav dej. Tsis tas li ntawd, raws li cov kav dej brine ua rau cov kua dej tib yam. tiv thaiv cov oxide txheej thiab tuaj yeem ua rau pitting corrosion.Txawm li cas los tiv thaiv cov kab mob no, ua kom koj cov kav dej huv los ntawm kev yaug lawv nrog dej tshiab.
Daim duab 1 - 316/316L stainless hlau yeeb nkab kis nrog acid, brine thiab lwm yam deposits yog heev raug rau pitting corrosion.
Feem ntau, pitting tuaj yeem txheeb xyuas tau yooj yim los ntawm tus neeg teb xov tooj.Txawm li cas los xij, crevice corrosion tsis yooj yim los kuaj xyuas thiab ua rau muaj kev pheej hmoo ntau dua rau cov neeg ua haujlwm thiab cov neeg ua haujlwm.Nws feem ntau tshwm sim ntawm cov kav dej uas muaj qhov chaw nruj ntawm cov khoom nyob ib puag ncig, xws li cov kav dej tuav hauv qhov chaw nrog cov clips lossis cov kav dej uas nruj nreem ntsia ntawm sab. (FeCl3) tov cov ntaub ntawv nyob rau hauv lub cheeb tsam lub sij hawm thiab ua kom ceev crevice corrosion (Daim duab 2).Vim crevices lawv tus kheej ua rau muaj kev pheej hmoo ntawm corrosion, crevice corrosion tuaj yeem tshwm sim ntawm qhov kub thiab txias ntau dua pitting corrosion.
Daim duab 2 - Crevice corrosion kuj tuaj yeem txhim kho 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 ferric chloride tov hauv qhov crevice.
Crevice corrosion feem ntau simulates pitting corrosion ua ntej nyob rau hauv lub crevice tsim ntawm ib tug ntev ntawm cov yeeb nkab thiab cov yeeb nkab txhawb clip.Txawm li cas los xij, vim qhov nce Fe ++ concentration nyob rau hauv cov kua hauv lub pob txha, qhov pib crater loj dua thiab loj dua kom txog thaum nws npog tag nrho cov pob txha. Thaum kawg, crevice corrosion tuaj yeem perforate cov yeeb nkab.
Cov kab nrib pleb yog qhov kev pheej hmoo loj tshaj plaws ntawm corrosion.Yog li ntawd, cov yeeb nkab clamps uas qhwv ib ncig ntawm feem ntau ntawm cov yeeb nkab ib ncig ntawm cov yeeb nkab yuav muaj kev pheej hmoo ntau dua li qhib clamps, uas txo qhov kev sib cuag ntawm cov yeeb nkab thiab cov clamp. Cov kws kho mob tuaj yeem pab txo qis qhov tshwm sim ntawm crevice corrosion ua kev puas tsuaj los yog tsis ua hauj lwm los ntawm kev qhib lub clamps thiab tshuaj xyuas qhov chaw ntawm cov yeeb nkab rau corrosion.
Pitting thiab crevice corrosion tuaj yeem tiv thaiv tau zoo tshaj plaws los ntawm kev xaiv cov hlau hlau zoo rau daim ntawv thov.Specifiers yuav tsum siv zog los xaiv cov khoom siv zoo tshaj plaws los txo qhov kev pheej hmoo ntawm corrosion raws li qhov chaw ua haujlwm, 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 cov hlau 'PREN qhov tseem ceeb los txiav txim siab lawv cov kev tiv thaiv hauv zos corrosion.PREN tuaj yeem xam los ntawm cov tshuaj muaj pes tsawg leeg ntawm cov 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 chromium, molybdenum thiab nitrogen nyob rau hauv lub alloy.Qhov kev sib raug zoo PREN yog raws li qhov tseem ceeb pitting kub (CPT) - qhov qis tshaj kub ntawm pitting corrosion yog pom - rau ntau yam stainless steels nyob rau hauv kev sib raug rau tshuaj muaj pes tsawg leeg.Qhov tseem ceeb, PREN yog proportional rau CPT.Yog li ntawd, me me nyob rau hauv pitting corrosion kuj. PREN tsuas yog sib npaug rau qhov me me ntawm CPT piv rau cov hlau, qhov kev nce loj hauv PREN qhia tau hais tias kev txhim kho tseem ceeb hauv kev ua tau zoo rau CPT siab dua.
Table 1 piv cov PREN qhov tseem ceeb ntawm ntau yam alloys feem ntau siv nyob rau hauv offshore roj thiab roj daim ntaub ntawv.Nws qhia tau hais tias yuav ua li cas cov specification yuav ho txhim kho corrosion los ntawm xaiv ib tug siab dua cov yeeb nkab alloy.PREN nce me ntsis thaum hloov los ntawm 316 mus rau 317 stainless hlau.Rau ib tug tseem ceeb kev ua tau zoo nce, 6 Mo super austenitic stainless hlau los yog 250 stainless hlau lub tswv yim yog super plexus.
Cov ntsiab lus ntau dua ntawm npib tsib xee (Ni) hauv stainless hlau kuj txhim khu kev tiv thaiv corrosion.Txawm li cas los xij, cov ntsiab lus npib tsib xee ntawm stainless hlau tsis yog ib feem ntawm PREN equation.Txawm li cas los xij, nws feem ntau tau txais txiaj ntsig los qhia cov hlau tsis muaj cov nickel ntau dua, vim tias lub ntsiab lus no yuav pab rov ua cov kab mob uas pom cov cim ntawm cov kab mob khaub thuas. kos 1/8 nyuaj yeeb nkab.Martensite yog ib qho tsis xav tau crystalline theem nyob rau hauv cov hlau uas txo cov hlau tsis muaj steel tsis kam rau hauv zos corrosion nrog rau cov tshuaj chloride-induced stress cracking.A cov nickel ntau dua ntawm tsawg kawg yog 12% hauv 316/316L kuj yog qhov xav tau rau cov ntawv thov uas muaj kev kub siab gaseous hydrogen.Qhov tsawg kawg nkaus 31M stainless hlau cov ntsiab lus yuav tsum tau muaj. 10%.
Localized corrosion tuaj yeem tshwm sim nyob txhua qhov chaw ntawm cov kav dej siv nyob rau hauv marine ib puag ncig.Txawm li cas los xij, pitting corrosion feem ntau yuav tshwm sim nyob rau hauv cov cheeb tsam uas twb muaj kab mob, thaum crevice corrosion yog feem ntau tshwm sim nyob rau hauv cov cheeb tsam uas nqaim qhov sib txawv ntawm cov yeeb nkab thiab cov mounting hardware.Siv PREN raws li lub hauv paus, tus specifier muaj peev xwm xaiv qhov zoo tshaj plaws yeeb nkab alloy kom txo tau qhov kev pheej hmoo ntawm txhua yam ntawm localized corrosion.
Txawm li cas los xij, nco ntsoov tias muaj lwm yam hloov pauv uas tuaj yeem cuam tshuam txog kev pheej hmoo corrosion.Piv txwv li, kub cuam tshuam rau pitting tsis kam ntawm stainless hlau.Rau cov huab cua sov marine, 6 molybdenum super austenitic los yog 2507 super duplex stainless hlau yeeb nkab yuav tsum raug txiav txim siab vim tias cov ntaub ntawv no muaj kev tiv thaiv zoo heev rau hauv cheeb tsam corrosion thiab chloride stress cracking.Rau cov huab cua txias 16 / 1L, qhov kev nyab xeeb ntawm 16 / 1L yog qhov zoo tshaj plaws. siv tau tsim.
Offshore platform cov tswv thiab cov tswv lag luam tseem tuaj yeem ua cov kauj ruam los txo qhov kev pheej hmoo ntawm kev xeb tom qab cov tubing tau teeb tsa.Lawv yuav tsum ua kom cov kav dej huv thiab yaug nrog cov dej tshiab tsis tu ncua kom tsis txhob muaj kev pheej hmoo ntawm pitting corrosion.Lawv yuav tsum muaj cov kws kho mob qhib tubing clamps thaum lub sij hawm niaj hnub tshuaj xyuas los saib xyuas qhov muaj cov kab mob corrosion.
Ua raws li cov kauj ruam uas tau teev tseg saum toj no, cov tswv platform thiab cov tswv lag luam tuaj yeem txo qhov kev pheej hmoo ntawm tubing corrosion thiab cuam tshuam txog kev xau hauv marine ib puag ncig, txhim kho kev nyab xeeb thiab kev ua haujlwm zoo, thaum txo cov khoom lag luam poob lossis kev tso tawm ntawm kev khiav tawm.
Brad Bollinger is the Oil and Gas Marketing Manager for Swagelok Company.He can be reached at bradley.bollinger@swagelok.com.
Phau ntawv Journal of Petroleum Technology yog cov ntawv xov xwm tseem ceeb ntawm Lub Koom Haum ntawm Petroleum Engineers, muab cov lus qhia luv luv thiab cov yam ntxwv ntawm kev nce qib hauv kev tshawb nrhiav thiab tsim cov thev naus laus zis, roj thiab roj teeb meem kev lag luam, thiab xov xwm hais txog SPE thiab nws cov tswv cuab.