Nangona imibhobho yentsimbi engagqwaliyo inamandla okugqwala, imibhobho yentsimbi engagqwaliyo efakwe kwiindawo zaselwandle ihlangabezana neentlobo ezahlukeneyo zokugqwala ngexesha lokuphila kwayo okulindelekileyo. Oku kugqwala kunokukhokelela ekukhutshweni komoya okubalekayo, ukulahleka kwemveliso kunye neengozi ezinokubakho. Abanini beqonga langaphandle kolwandle kunye nabaqhubi banokunciphisa umngcipheko wokugqwala ngokuchaza izixhobo zepayipi ezinamandla ezibonelela ngokuxhathisa okungcono kokugqwala. Emva koko, kufuneka bahlale bephaphile xa behlola i-chemical injection, i-hydraulic kunye ne-impulse lines, kunye nezixhobo zokucubungula kunye nezixhobo zokuva ukuqinisekisa ukuba ukugqwala akusongeli ukuthembeka kwemibhobho efakiweyo kwaye kubeke emngciphekweni ukhuseleko.
Ukugqwala kwendawo ethile kunokufumaneka kumaqonga amaninzi, kwiinqanawa, kwiinqanawa, nakwiipayipi kwiindawo ezifakelwe ngaphandle kolwandle. Oku kugqwala kunokuba ngendlela yokugqwala kwemingxuma okanye imingxuma, nokuba yeyiphi na kwezi enokonakalisa udonga lombhobho kwaye ibangele ukukhutshwa kolwelo.
Umngcipheko wokugqwala mkhulu xa ubushushu bokusebenza kwesicelo busanda. Ubushushu bunokukhawulezisa ukutshatyalaliswa kwefilimu ye-oxide yangaphandle ekhuselayo yetyhubhu, ngaloo ndlela kukhuthaze ukwakheka kokugqwala kwemingxuma.
Ngelishwa, ukugqwala kwendawo kunye nokugqwala kwemingxuma kunokuba nzima ukukubona, okwenza olu hlobo lokugqwala lube nzima ukulichonga, ukuliqikelela nokuyila. Ngenxa yezi ngozi, abanini beqonga, abaqhubi kunye nabakhethiweyo kufuneka balumke xa bekhetha izixhobo zombhobho ezilungileyo zokusetyenziswa kwabo. Ukukhetha izinto yindlela yabo yokuqala yokuzikhusela ekugqwaleni, ngoko ke ukwenza okulungileyo kubalulekile. Ngethamsanqa, banokukhetha ukusebenzisa indlela elula kodwa esebenzayo yokulinganisa ukugqwala kwendawo, iPitting Resistance Equivalent Number (PREN). Okukhona ixabiso lePREN lesinyithi liphezulu, kokukhona ukuxhathisa kwayo ukugqwala kwendawo.
Eli nqaku liza kuphonononga indlela yokuchonga umhlwa ophuma kwimingxuma kunye nemingxuma kunye nendlela yokuphucula ukukhethwa kwezinto zetyhubhu kwiindlela zeoyile kunye negesi ezisetyenziswa elwandle ngokusekelwe kwixabiso le-PREN yezixhobo.
Ukugqwala kwendawo kwenzeka kwiindawo ezincinci xa kuthelekiswa nokugqwala okuqhelekileyo, okufana ngakumbi kumphezulu wesinyithi. Ukugqwala kwemingxuma kunye nemingxuma kuqala ukwenzeka kwiipayipi zentsimbi engagqwali ezingama-316 xa ifilimu yangaphandle yesinyithi ene-chromium eninzi igqabhuka ngenxa yokuvezwa kulwelo olugqwalisiweyo, kuquka amanzi anetyuwa. Iindawo zaselwandle ezityebileyo elunxwemeni naselwandle olune-chloride eninzi, kunye namaqondo obushushu aphezulu kunye nongcoliseko lomphezulu weetyhubhu, kwandisa amathuba okuwohloka kwale filimu yokugqwala.
ukugqwala kwemigodi. Ukugqwala kwemigodi kwenzeka xa ifilimu yokudlula kubude bombhobho itshatyalalisiwe, yenze imingxunya emincinci okanye imingxuma kumphezulu wombhobho. Ezo mingxuma zinokukhula njengoko kwenzeka ii-electrochemical reactions, nto leyo ebangela ukuba isinyithi esikwisinyithi sinyibilike kwisisombululo esisezantsi komngxuma. Isinyithi esinyibilikisiweyo siya kuthi emva koko sisasazeke siye phezulu komngxuma size sinyibilike senze i-iron oxide okanye i-rust. Njengoko umngxuma usiba nzulu, ii-electrochemical reactions ziyakhawuleza, ukugqwala kuyaqina, kwaye kunokukhokelela ekugqobhozeni kodonga lombhobho kwaye kukhokelele ekuvuzeni.
Ukuthuthwa kwemibhobho kuchaphazeleka lula kukubola kwemigodi xa umphezulu wayo wangaphandle ungcolisiwe (Umfanekiso 1). Umzekelo, ukungcoliswa okuvela kwimisebenzi yokuwelda kunye nokugaya kunokonakalisa umaleko we-oxide odlulayo wombhobho, ngaloo ndlela kudale kwaye kukhawulezise ukubola kwemigodi. Oku kuyafana nangokujongana nokungcoliswa yimibhobho. Ukongeza, njengoko amathontsi etyuwa ephuma, iikristale zetyuwa ezimanzi ezikwimibhobho zenza okufanayo ukukhusela umaleko we-oxide kwaye zinokukhokelela ekuboleni kwemigodi. Ukuthintela olu hlobo lokungcoliswa, gcina imibhobho yakho icocekile ngokuyihlamba rhoqo ngamanzi amatsha.
Umfanekiso 1 – Umbhobho wentsimbi engagqwaliyo oyi-316/316L ongcoliswe yi-asidi, ityuwa kunye nezinye izinto ezidityanisiweyo usengozini enkulu yokubola kwemingxuma.
Ukubola kwe-crevice. Kwiimeko ezininzi, ukubola kwe-crevice kunokubonwa lula ngumsebenzisi. Nangona kunjalo, ukubola kwe-crevice akulula ukukubona kwaye kubeka umngcipheko omkhulu kubasebenzi nakubasebenzi. Ngokuqhelekileyo kwenzeka kwiipayipi ezineendawo ezixineneyo phakathi kwezinto ezijikelezileyo, ezifana neepayipi ezibanjwe endaweni enezikliphu okanye iipayipi ezifakwe ngokuqinileyo ecaleni. Xa i-brine ingena kwi-crevice, isisombululo se-ferric chloride (FeCl3) esinoburhalarhume esinoburhalarhume sakha kuloo ndawo ngokuhamba kwexesha kwaye sibangele ukubola kwe-crevice okukhawulezileyo (Umfanekiso 2). Ngenxa yokuba ii-crevices ngokwazo zandisa umngcipheko wokubola, ukubola kwe-crevice kunokwenzeka kumaqondo obushushu aphantsi kakhulu kunokubola kwe-pitting.
Umfanekiso 2 – Ukubola komngxuma kungavela phakathi kombhobho kunye nenkxaso yombhobho (phezulu) kwaye xa umbhobho ufakwe kufutshane nezinye iindawo (ezantsi) ngenxa yokwenziwa kwesisombululo se-ferric chloride esinoburhalarhume obunamandla kwiikhemikhali kwimngxuma.
Ukubola kwe-crevice kudla ngokuxelisa ukubola kwe-pitting kuqala kwi-cravice eyenziwe phakathi kobude bombhobho kunye ne-clip yokuxhasa umbhobho. Nangona kunjalo, ngenxa yokwanda koxinzelelo lwe-Fe++ kulwelo ngaphakathi kwe-fracture, i-crater yokuqala iba nkulu kwaye ibe nkulu ide igubungele yonke i-fracture. Ekugqibeleni, ukubola kwe-crevice kunokugqobhoza umbhobho.
Iimfanta eziqinileyo zezona zinobungozi obukhulu bokugqwala. Ke ngoko, ii-clamps zepayipi ezijikeleza uninzi lomjikelezo wombhobho zidla ngokuba nomngcipheko omkhulu kunee-clamps ezivulekileyo, ezinciphisa umphezulu woqhagamshelwano phakathi kombhobho kunye ne-clamp. Iingcali zokulungisa zinokunceda ukunciphisa amathuba okuba ukugqwala okuqhekekileyo kubangele umonakalo okanye ukungaphumeleli ngokuvula rhoqo ii-clamps kunye nokuhlola umphezulu wombhobho ukuba awugqwali na.
Ukugqwala kwe-pitting kunye ne-cravice kungathintelwa ngcono ngokukhetha i-alloy yesinyithi efanelekileyo yokusetyenziswa. Abachazi-magama kufuneka basebenzise unonophelo olufanelekileyo lokukhetha izixhobo zombhobho ezifanelekileyo ukunciphisa umngcipheko wokugqwala ngokusekelwe kwindawo yokusebenza, iimeko zenkqubo kunye nezinye izinto eziguquguqukayo.
Ukunceda abachazi-magama baphucule ukukhethwa kwezinto, banokuthelekisa amaxabiso e-PREN eentsimbi ukuze bafumanise ukumelana kwazo nokugqwala kwendawo. I-PREN ingabalwa ngokweekhemikhali ze-alloy, kuquka i-chromium (Cr), i-molybdenum (Mo), kunye nomxholo we-nitrogen (N), ngolu hlobo lulandelayo:
I-PREN iyanda ngomxholo we-chromium, i-molybdenum kunye ne-nitrogen kwi-alloy. Ubudlelwane be-PREN busekelwe kubushushu obubalulekileyo be-pitting (CPT) - ubushushu obuphantsi apho i-pitting corrosion ibonwa khona - kwiintsimbi ezahlukeneyo ezingenasici ngokumalunga nokwakheka kweekhemikhali. Ngokuyintloko, i-PREN ilingana ne-CPT. Ke ngoko, amaxabiso aphezulu e-PREN abonisa ukumelana okuphezulu kwe-pitting. Ukunyuka okuncinci kwe-PREN kufana nokunyuka okuncinci kwe-CPT xa kuthelekiswa ne-alloy, ngelixa ukunyuka okukhulu kwe-PREN kubonisa ukuphucuka okukhulu ekusebenzeni ukuya kwi-CPT ephezulu kakhulu.
Itheyibhile 1 ithelekisa amaxabiso e-PREN ee-alloys ezahlukeneyo ezisetyenziswa rhoqo kwizicelo zeoyile kunye negesi ezikude nolwandle. Ibonisa indlela iinkcukacha ezinokuphucula ngayo kakhulu ukumelana nokugqwala ngokukhetha i-alloy yombhobho yodidi oluphezulu. I-PREN inyuka kancinci kuphela xa itshintsha ukusuka kwi-316 ukuya kwi-317 yentsimbi engagqwali. Ukunyusa ukusebenza okubonakalayo, i-6 Mo super austenitic stainless steel okanye i-2507 super duplex stainless steel ifanelekile ukusetyenziswa.
Ubuninzi be-nickel (Ni) kwintsimbi engagqwaliyo bukwaphucula ukumelana nokugqwala. Nangona kunjalo, umxholo we-nickel kwintsimbi engagqwaliyo awuyonxalenye ye-PREN equation. Nokuba kunjalo, kudla ngokuba luncedo ukuchaza iintsimbi ezingagqwaliyo ezinezinga eliphezulu ze-nickel, njengoko le nto inceda ukuphinda itshintshe indawo ezibonisa iimpawu zokugqwala kwendawo. I-nickel izinzisa i-austenite kwaye ithintele ukwakheka kwe-martensite xa igoba okanye itsala umbhobho oqinileyo we-1/8. I-Martensite sisigaba sekristale esingafunekiyo kwiintsimbi esinciphisa ukumelana kwentsimbi engagqwaliyo kwi-corrosion yendawo kunye nokuqhekeka koxinzelelo olubangelwa yi-chloride. Ubungakanani be-nickel obuphezulu obuyi-12% kwi-316/316L bukwafanelekile kwizicelo ezibandakanya i-hydrogen yegesi enoxinzelelo oluphezulu. Ubungakanani obuncinci be-nickel obufunekayo kwintsimbi engagqwali ye-316/316L kwi-ASTM standard specification yi-10%.
Ukugqwala kwendawo ethile kunokwenzeka naphi na kwiipayipi ezisetyenziswa kwiindawo zaselwandle. Nangona kunjalo, ukugqwala kwemigodi kunokwenzeka kakhulu kwiindawo esele zingcolisiwe, ngelixa ukugqwala kwemingxuma kunokwenzeka kakhulu kwiindawo ezinezikhewu ezincinci phakathi kombhobho kunye nezixhobo zokufakela. Isebenzisa i-PREN njengesiseko, i-specifier inokukhetha i-alloy yombhobho efanelekileyo ukunciphisa umngcipheko walo naluphi na uhlobo lokugqwala kwendawo ethile.
Nangona kunjalo, khumbula ukuba kukho ezinye izinto ezinokuchaphazela umngcipheko wokugqwala. Umzekelo, ubushushu buchaphazela ukumelana kwentsimbi engagqwaliyo. Kwimozulu eshushu yaselwandle, umbhobho wentsimbi engagqwaliyo oyi-6 molybdenum super austenitic okanye i-2507 super duplex kufuneka uqwalaselwe nzulu kuba ezi zinto zinokumelana okuhle kakhulu nokugqwala kwendawo kunye nokuqhekeka koxinzelelo lwe-chloride. Kwimozulu epholileyo, umbhobho we-316/316L unokwanela, ingakumbi ukuba imbali yokusetyenziswa ngempumelelo sele imiselwe.
Abanini beeplatifomu zangaphandle kunye nabaqhubi banokuthatha amanyathelo okunciphisa umngcipheko wokugqwala emva kokuba iityhubhu zifakiwe. Bafanele bagcine iipayipi zicocekile kwaye zihlanjwe ngamanzi acocekileyo rhoqo ukunciphisa umngcipheko wokugqwala kwemingxuma. Bafanele babe neengcali zokulungisa ezivula ii-tubing clamps ngexesha lokuhlolwa rhoqo ukujonga ubukho bokugqwala kwemingxuma.
Ukulandela amanyathelo achaziweyo apha ngasentla, abanini beqonga kunye nabaqhubi banokunciphisa umngcipheko wokugqwala kweetyhubhu kunye nokuvuza okunxulumene noko kwiindawo zaselwandle, baphucule ukhuseleko kunye nokusebenza kakuhle, ngelixa benciphisa amathuba okulahleka kwemveliso okanye ukukhutshwa komoya ophumayo.
Brad Bollinger is the Oil and Gas Marketing Manager for Swagelok Company.He can be reached at bradley.bollinger@swagelok.com.
I-Journal of Petroleum Technology yimagazini ephambili ye-Society of Petroleum Engineers, enika iingxelo ezichanekileyo kunye neempawu malunga nokuqhubela phambili kubuchwepheshe bokuhlola nokuvelisa, imiba yeshishini leoyile negesi, kunye neendaba malunga ne-SPE kunye namalungu ayo.