Txawm hais tias cov kav dej hlau tsis xeb muaj qhov tiv taus xeb, cov kav dej hlau tsis xeb uas tau teeb tsa hauv cov chaw nyob hauv dej hiav txwv raug ntau hom xeb thaum lub sijhawm ua haujlwm. Qhov xeb no tuaj yeem ua rau muaj pa phem, poob khoom thiab muaj kev pheej hmoo. Cov tswv thiab cov neeg ua haujlwm ntawm Offshore platform tuaj yeem txo qhov kev pheej hmoo ntawm kev xeb los ntawm kev teev cov khoom siv yeeb nkab muaj zog dua uas muab kev tiv taus xeb zoo dua. Tom qab ntawd, lawv yuav tsum ceev faj thaum tshuaj xyuas cov kab txhaj tshuaj, cov kab hydraulic thiab impulse, thiab cov cuab yeej ua haujlwm thiab cov cuab yeej siv kom ntseeg tau tias kev xeb tsis hem kev ncaj ncees ntawm cov kav dej uas tau teeb tsa lossis ua rau muaj kev nyab xeeb.
Kev xeb hauv zos tuaj yeem pom ntawm ntau lub platform, nkoj, thiab cov kav dej hauv hiav txwv. Qhov kev xeb no tuaj yeem yog nyob rau hauv daim ntawv ntawm kev xeb pitting lossis crevice, ob qho tib si tuaj yeem ua rau lub yeeb nkab phab ntsa thiab ua rau cov kua dej tawm.
Qhov kev pheej hmoo ntawm kev xeb nce ntxiv thaum qhov kub ua haujlwm ntawm daim ntawv thov nce ntxiv. Kub tuaj yeem ua rau lub raj xa dej puas tsuaj sai dua, yog li ua rau muaj kev puas tsuaj.
Tu siab kawg li, qhov xeb ntawm qhov chaw thiab qhov tawg ntawm qhov chaw nyuaj nrhiav pom, ua rau nws nyuaj rau txheeb xyuas, kwv yees, thiab tsim cov xeb no. Vim muaj cov kev pheej hmoo no, cov tswv platform, cov neeg ua haujlwm thiab cov neeg raug xaiv yuav tsum ceev faj thaum xaiv cov khoom siv kav dej zoo tshaj plaws rau lawv daim ntawv thov. Kev xaiv cov khoom siv yog lawv thawj kab tiv thaiv kev xeb, yog li kev ua kom raug yog qhov tseem ceeb heev. Hmoov zoo, lawv tuaj yeem xaiv qhov kev ntsuas yooj yim tab sis zoo heev ntawm kev tiv thaiv kev xeb hauv zos, tus lej Pitting Resistance Equivalent (PREN). Tus nqi PREN siab dua ntawm cov hlau, qhov siab dua nws qhov kev tiv thaiv rau kev xeb hauv zos.
Tsab xov xwm no yuav saib seb yuav ua li cas thiaj paub qhov xeb ntawm qhov pitting thiab crevice, nrog rau yuav ua li cas thiaj li ua kom zoo dua cov khoom siv raj rau kev siv roj thiab roj av hauv hiav txwv raws li tus nqi PREN ntawm cov khoom.
Kev xeb hauv zos tshwm sim hauv thaj chaw me me piv rau kev xeb dav dav, uas yog sib xws ntau dua ntawm qhov chaw hlau. Kev xeb pitting thiab crevice pib tsim ntawm 316 stainless hlau tubing thaum cov chromium-nplua nuj passive oxide zaj duab xis ntawm cov hlau tawg vim yog kev raug rau cov kua corrosive, suav nrog dej ntsev. Cov chaw nyob hauv dej hiav txwv nplua nuj hauv chlorides, nrog rau qhov kub siab thiab txawm tias muaj kuab paug ntawm qhov chaw tubing, ua rau muaj kev puas tsuaj ntawm zaj duab xis passivation no.
Kev xeb pitting tshwm sim thaum daim zaj duab xis passivation ntawm ib ntu ntawm cov yeeb nkab tawg, tsim cov qhov me me lossis qhov ntawm qhov saum npoo ntawm cov yeeb nkab. Cov qhov no yuav loj hlob thaum cov tshuaj electrochemical ua mus, vim li ntawd cov hlau hauv cov hlau yaj hauv cov tshuaj ntawm qab ntawm qhov. Cov hlau yaj ces yuav kis mus rau saum qhov thiab oxidize kom tsim cov hlau oxide lossis xeb. Thaum lub qhov tob zuj zus, cov tshuaj electrochemical ua kom nrawm dua, kev xeb nce ntxiv, uas tuaj yeem ua rau lub yeeb nkab tawg thiab ua rau xau.
Cov kav dej yuav yooj yim rau qhov pitting yog tias lawv qhov chaw sab nraud muaj kuab paug (Daim Duab 1). Piv txwv li, cov kuab paug los ntawm kev vuam thiab kev sib tsoo tuaj yeem ua rau lub txheej oxide passivation ntawm cov kav dej puas tsuaj, yog li tsim thiab ua kom cov pitting sai dua. Tib yam li ntawd rau kev daws teeb meem nrog cov kuab paug los ntawm cov kav dej. Tsis tas li ntawd, thaum cov ntsev poob ua pa, cov ntsev ntub dej uas tsim rau ntawm cov kav dej tiv thaiv cov txheej oxide thiab tuaj yeem ua rau muaj kuab paug. Txhawm rau tiv thaiv cov hom kev paug no, khaws koj cov kav dej kom huv si los ntawm kev yaug lawv tsis tu ncua nrog dej tshiab.
Daim Duab 1. Cov yeeb nkab hlau tsis xeb 316/316L uas muaj kua qaub, ntsev, thiab lwm yam khoom tso tawm yuav yooj yim rau kev tawg.
Kev xeb ntawm qhov tawg. Feem ntau, tus neeg teb xov tooj tuaj yeem pom qhov pitting yooj yim. Txawm li cas los xij, kev xeb ntawm qhov tawg tsis yooj yim pom thiab ua rau muaj kev pheej hmoo ntau dua rau cov neeg teb xov tooj thiab cov neeg ua haujlwm. Qhov no feem ntau tshwm sim rau cov kav dej uas muaj qhov sib txawv nqaim ntawm cov khoom siv ib puag ncig, xws li cov kav dej uas tuav rau hauv qhov chaw nrog cov clamps lossis cov kav dej uas tau ntim nruj nreem ib sab. Thaum cov dej ntsev nkag mus rau hauv qhov tawg, dhau sijhawm, cov tshuaj lom neeg acidified ferric chloride (FeCl3) tau tsim nyob rau hauv thaj chaw no, uas ua rau kev xeb ntawm qhov tawg sai dua (Daim Duab 2). Vim tias qhov tawg nws tus kheej ua rau muaj kev pheej hmoo ntawm kev xeb, kev xeb ntawm qhov tawg tuaj yeem tshwm sim ntawm qhov kub qis dua li qhov tawg.
Daim Duab 2 - Kev xeb tawg tuaj yeem tshwm sim ntawm cov yeeb nkab thiab cov yeeb nkab txhawb nqa (sab saud) thiab thaum cov yeeb nkab raug teeb tsa ze rau lwm qhov chaw (hauv qab) vim yog kev tsim cov tshuaj lom neeg ua kua qaub ntawm ferric chloride hauv qhov sib txawv.
Feem ntau qhov xeb ntawm qhov tawg ua tej daim me me ua rau lub qhov khoob ua ntej hauv qhov sib txawv ntawm ntu yeeb nkab thiab lub dab tshos txhawb yeeb nkab. Txawm li cas los xij, vim muaj kev nce ntxiv ntawm Fe++ hauv cov kua dej hauv qhov tawg, lub raj pib loj zuj zus mus txog thaum nws npog tag nrho qhov tawg. Thaum kawg, qhov xeb ntawm qhov tawg tuaj yeem ua rau lub yeeb nkab tawg.
Cov kab nrib pleb ntom ntom yog qhov muaj feem yuav xeb ntau tshaj plaws. Yog li ntawd, cov clamps yeeb nkab uas puag ncig ib feem loj ntawm cov yeeb nkab feem ntau muaj kev pheej hmoo ntau dua li cov clamps qhib, uas ua rau qhov chaw sib cuag ntawm cov yeeb nkab thiab clamp tsawg dua. Cov kws kho tshuab tuaj yeem pab txo qhov muaj feem yuav puas tsuaj lossis ua tsis tiav ntawm qhov tawg los ntawm kev qhib cov clamps thiab kuaj xyuas qhov chaw ntawm cov yeeb nkab kom paub meej tias puas xeb.
Kev xeb ntawm qhov pitting thiab qhov tawg tuaj yeem tiv thaiv tau los ntawm kev xaiv cov hlau sib xyaw kom raug rau daim ntawv thov. Cov neeg teev lus qhia yuav tsum ua tib zoo xaiv cov khoom siv kav dej zoo tshaj plaws kom txo qhov kev pheej hmoo ntawm kev xeb nyob ntawm qhov chaw ib puag ncig, cov xwm txheej ntawm cov txheej txheem, thiab lwm yam.
Yuav kom pab cov neeg tshwj xeeb xaiv cov khoom siv zoo tshaj plaws, lawv tuaj yeem piv cov nqi PREN ntawm cov hlau los txiav txim siab lawv qhov kev tiv thaiv rau qhov xeb hauv zos. PREN tuaj yeem suav los ntawm cov tshuaj lom neeg 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 rau cov ntsiab lus ntawm cov khoom tiv taus corrosion ntawm chromium, molybdenum thiab nitrogen hauv cov hlau alloy. Qhov piv ntawm PREN yog raws li qhov kub thiab txias tseem ceeb (CPT) - qhov kub qis tshaj plaws uas pitting tshwm sim - rau ntau yam hlau stainless nyob ntawm cov tshuaj lom neeg sib xyaw. Yeej, PREN yog proportional rau CPT. Yog li ntawd, cov nqi PREN siab dua qhia txog kev tiv thaiv pitting siab dua. Kev nce me me hauv PREN tsuas yog sib npaug rau kev nce me me hauv CPT piv rau cov hlau alloy, thaum kev nce loj hauv PREN qhia txog kev txhim kho tseem ceeb hauv kev ua tau zoo dua li CPT siab dua.
Rooj 1 piv cov nqi PREN rau ntau yam alloys feem ntau siv hauv kev lag luam roj thiab roj av hauv hiav txwv. Nws qhia tau hais tias qhov kev qhia tshwj xeeb tuaj yeem txhim kho qhov kev tiv thaiv corrosion los ntawm kev xaiv cov yeeb nkab zoo dua. PREN nce me ntsis ntawm 316 SS mus rau 317 SS. Super Austenitic 6 Mo SS lossis Super Duplex 2507 SS yog qhov zoo tagnrho rau kev nce qib tseem ceeb hauv kev ua tau zoo.
Cov nickel (Ni) ntau dua hauv cov hlau tsis xeb kuj ua rau muaj kev tiv thaiv xeb ntau dua. Txawm li cas los xij, cov ntsiab lus nickel ntawm cov hlau tsis xeb tsis yog ib feem ntawm PREN equation. Txawm li cas los xij, nws feem ntau zoo dua los xaiv cov hlau tsis xeb uas muaj cov ntsiab lus nickel ntau dua, vim tias cov khoom no pab rov ua kom cov nplaim uas qhia txog kev xeb hauv zos. Nickel ua kom ruaj khov austenite thiab tiv thaiv kev tsim martensite thaum khoov lossis kos txias 1/8 lub yeeb nkab. Martensite yog ib theem crystalline tsis xav tau hauv cov hlau uas txo qhov kev tiv thaiv ntawm cov hlau tsis xeb rau kev xeb hauv zos nrog rau chloride-induced kev ntxhov siab tawg. Cov ntsiab lus nickel ntau dua ntawm tsawg kawg 12% hauv 316/316L hlau kuj xav tau rau kev siv roj hydrogen siab. Qhov tsawg kawg nkaus nickel concentration xav tau rau ASTM 316/316L hlau tsis xeb yog 10%.
Kev xeb hauv zos tuaj yeem tshwm sim txhua qhov chaw ntawm cov kav dej siv hauv cov chaw nyob hauv dej hiav txwv. Txawm li cas los xij, qhov pitting feem ntau yuav tshwm sim hauv cov cheeb tsam uas twb muaj kuab paug lawm, thaum qhov crevice xeb feem ntau yuav tshwm sim hauv cov cheeb tsam uas muaj qhov sib txawv nqaim ntawm cov kav dej thiab cov khoom siv teeb tsa. Siv PREN ua lub hauv paus, tus neeg teev tseg tuaj yeem xaiv cov yeeb nkab alloy zoo tshaj plaws kom txo qhov kev pheej hmoo ntawm txhua yam kev xeb hauv zos.
Txawm li cas los xij, nco ntsoov tias muaj lwm yam uas tuaj yeem cuam tshuam rau qhov kev pheej hmoo ntawm kev xeb. Piv txwv li, qhov kub thiab txias cuam tshuam rau qhov tsis kam ntawm cov hlau tsis xeb rau pitting. Rau cov huab cua kub maritime, super austenitic 6 molybdenum hlau 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 heev rau kev xeb hauv zos thiab chloride tawg. Rau cov huab cua txias dua, 316/316L yeeb nkab yuav txaus, tshwj xeeb tshaj yog tias muaj keeb kwm ntawm kev siv tau zoo.
Cov tswv thiab cov neeg ua haujlwm ntawm lub platform offshore kuj tuaj yeem ua cov kauj ruam los txo qhov kev pheej hmoo ntawm kev xeb tom qab cov yeeb nkab tau teeb tsa lawm. Lawv yuav tsum khaws cov yeeb nkab kom huv si thiab ntxuav nrog dej tshiab tas li kom txo qhov kev pheej hmoo ntawm kev khawb. Lawv kuj yuav tsum muaj cov kws kho tshuab qhib cov clamps yeeb nkab thaum lub sijhawm tshuaj xyuas tas li kom paub tseeb tias puas muaj kev xeb ntawm qhov tawg.
Los ntawm kev ua raws li cov kauj ruam saum toj no, cov tswv thiab cov neeg ua haujlwm tuaj yeem txo qhov kev pheej hmoo ntawm kev xeb ntawm cov kav dej thiab cov xau hauv dej hiav txwv, txhim kho kev nyab xeeb thiab kev ua haujlwm zoo, thiab txo qhov muaj feem ntawm kev poob khoom lossis cov pa phem khiav tawm.
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 phau ntawv xov xwm tseem ceeb ntawm Society of Petroleum Engineers, uas muaj cov ntsiab lus tseem ceeb thiab cov ntawv sau txog kev nce qib hauv kev siv tshuab upstream, cov teeb meem kev lag luam roj thiab roj av, thiab xov xwm txog SPE thiab nws cov tswv cuab.