Naphezu kokumelana nokugqwala okungokwemvelo kwamapayipi ensimbi engagqwali, amapayipi ensimbi engagqwali afakwe ezindaweni zasolwandle abhekana nezinhlobo ezahlukene zokugqwala ngesikhathi sokuphila kwawo okulindelekile. Lokhu kugqwala kungaholela ekukhishweni komoya okubalekayo, ukulahlekelwa umkhiqizo kanye nezingozi ezingaba khona. Abanikazi beplatifomu yasogwini kanye nabaqhubi banganciphisa ingozi yokugqwala ngokucacisa izinto zepayipi eziqinile ezinikeza ukumelana nokugqwala okungcono. Ngemuva kwalokho, kumele bahlale beqaphile lapho behlola ukujova kwamakhemikhali, imigqa ye-hydraulic kanye ne-impulse, kanye nemishini yokucubungula kanye nemishini yokuzwa ukuqinisekisa ukuthi ukugqwala akusongeli ubuqotho bamapayipi afakiwe futhi kubeke engcupheni ukuphepha.
Ukugqwala kwendawo kungatholakala kumapulatifomu amaningi, emikhunjini, emikhunjini, kanye nasezindaweni zokufaka amapayipi ezindaweni ezingaphandle kolwandle. Lokhu kugqwala kungaba ngesimo sokugqwala kwemigodi noma i-crevice, noma yikuphi okungaguguleka udonga lwepayipi futhi kubangele ukukhishwa koketshezi.
Ingozi yokugqwala inkulu lapho izinga lokushisa lokusebenza lesicelo likhuphuka. Ukushisa kungasheshisa ukubhujiswa kwefilimu yangaphandle ye-oxide evikelayo yepayipi, ngaleyo ndlela kukhuthaze ukwakheka kokugqwala kwemigodi.
Ngeshwa, ukugqwala kwendawo kanye nokugqwala kwemigodi kungaba nzima ukukubona, okwenza lezi zinhlobo zokugqwala kube nzima ukuzibona, ukuzibikezela kanye nokuziklamela. Ngenxa yalezi zingozi, abanikazi beplatifomu, abaqhubi kanye nabaqokiwe kufanele baqaphele lapho bekhetha izinto zokufaka amapayipi ezingcono kakhulu zokusetshenziswa kwabo. Ukukhetha izinto kuyindlela yabo yokuqala yokuzivikela ekugqwaleni, ngakho-ke ukwenza kahle kubalulekile. Ngenhlanhla, bangakhetha ukusebenzisa isilinganiso esilula kodwa esisebenzayo kakhulu sokumelana nokugqwala kwendawo, i-Pitting Resistance Equivalent Number (PREN). Uma inani le-PREN lensimbi liphakeme, kulapho ukumelana kwayo nokugqwala kwendawo kuphakeme khona.
Lesi sihloko sizobuyekeza indlela yokubona ukugqwala kwemigodi kanye nemifantu kanye nendlela yokuthuthukisa ukukhethwa kwezinto zamapayipi okusetshenziswa kukawoyela negesi ogwini lolwandle ngokusekelwe enanini le-PREN yale nto.
Ukugqwala kwendawo kwenzeka ezindaweni ezincane uma kuqhathaniswa nokugqwala okuvamile, okufana kakhulu ebusweni bensimbi. Ukugqwala kwemigodi kanye nemisele kuqala ukwakheka emapayipini ensimbi angagqwali angu-316 lapho ifilimu yangaphandle yensimbi ecebile nge-chromium iqhuma ngenxa yokuchayeka eziwuketshezini ezigqwali, okuhlanganisa namanzi anosawoti. Izindawo zasolwandle ezicebile nge-chloride kanye nolwandle, kanye namazinga okushisa aphezulu ngisho nokungcoliswa kobuso bepayipi, kwandisa amathuba okuwohloka kwale filimu yokugqwala.
ukugqwala kwemigodi. Ukugqwala kwemigodi kwenzeka lapho ifilimu yokudlulisa amandla epayipini ubude ibhujiswa, kwakha imigodi emincane noma imigodi ebusweni bepayipi. Imigodi enjalo cishe izokhula njengoba kwenzeka ukusabela kwe-electrochemical, okubangela ukuthi insimbi ensimbini incibilike ibe yisisombululo phansi komgodi. Insimbi encibilikisiwe izobe isisabalala iye phezulu komgodi bese i-oxidize ukuze yakhe i-iron oxide noma ukugqwala. Njengoba umgodi ujula, ukusabela kwe-electrochemical kuyashesha, ukugqwala kuyaqina, futhi kungaholela ekubhobokeni kodonga lwepayipi futhi kuholele ekuvuzeni.
Ukufaka amapayipi kusengozini enkulu yokugqwala kwemigodi uma ubuso bawo bangaphandle bungcolisiwe (Isithombe 1). Isibonelo, ukungcola okuvela emisebenzini yokushisela nokugaya kungalimaza ungqimba lwe-oxide oludlulayo lwepayipi, ngaleyo ndlela kwakheke futhi kusheshise ukugqwala kwemigodi. Kungokufanayo nangokubhekana nokungcola okuvela emapayipini. Ngaphezu kwalokho, njengoba amaconsi e-brine ehwamuka, amakristalu kasawoti amanzi akheka emapayipini enza okufanayo ukuvikela ungqimba lwe-oxide futhi angaholela ekugqwaleni kwemigodi. Ukuze uvimbele lolu hlobo lokungcola, gcina amapayipi akho ehlanzekile ngokuwahlanza njalo ngamanzi ahlanzekile.
Umfanekiso 1 – Ipayipi lensimbi engagqwali elingu-316/316L elingcoliswe yi-asidi, i-brine kanye nezinye izinto ezisele lisengozini enkulu yokugqwala kwemigodi.
Ukugqwala kwe-crevice.Ezimweni eziningi, ukugqwala kwe-crevice kungabonakala kalula ngumqhubi.Kodwa-ke, ukugqwala kwe-crevice akulula ukukubona futhi kubeka ingozi enkulu kubaqhubi kanye nabasebenzi. Ngokuvamile kwenzeka emapayipini anezikhala eziqinile phakathi kwezinto ezizungezile, njengamapayipi abanjwe endaweni aneziqeshana noma amapayipi afakwe ngokuqinile eceleni. Lapho i-brine ingena e-crevice, isixazululo se-ferric chloride (FeCl3) esinolaka ngamakhemikhali sakha endaweni ngokuhamba kwesikhathi futhi sibangele ukugqwala kwe-crevice okusheshayo (Isithombe 2).Ngenxa yokuthi imifantu ngokwayo yandisa ingozi yokugqwala, ukugqwala kwe-crevice kungenzeka emazingeni okushisa aphansi kakhulu kunokugqwala kwe-pitting.
Umfanekiso 2 – Ukugqwala komfantu kungase kuvele phakathi kwepayipi kanye nokusekelwa kwepayipi (phezulu) nalapho ipayipi lifakwe eduze kwezinye izindawo (phansi) ngenxa yokwakheka kwesisombululo se-ferric chloride esinolaka ngamakhemikhali emfantwini.
Ukugqwala kwe-crevice kuvame ukulingisa ukugqwala kwe-pitting kuqala emngxunyeni owakhiwe phakathi kobude bepayipi kanye nesiqeshana sokusekela ipayipi. Kodwa-ke, ngenxa yokwanda kokuhlushwa kwe-Fe++ oketshezini olungaphakathi kokugqwala, i-crater yokuqala iba nkulu futhi ibe nkulu kuze kube yilapho imboza yonke i-fracture. Ekugcineni, ukugqwala kwe-crevice kungabhoboza ipayipi.
Imifantu eqinile iyingozi enkulu yokugqwala. Ngakho-ke, izibambo zamapayipi ezigoqa ingxenye enkulu yomjikelezo wepayipi zivame ukuveza ingozi enkulu kunezibambo ezivulekile, ezinciphisa indawo yokuxhumana phakathi kwepayipi nesibambo. Ochwepheshe bokulungisa bangasiza ekunciphiseni amathuba okugqwala kwemifantu okubangela umonakalo noma ukwehluleka ngokuvula njalo izibambo nokuhlola ubuso bepayipi ukuthi abugqwali yini.
Ukugqwala kwe-pitting kanye ne-crevice kungavinjelwa kangcono ngokukhetha i-alloy yensimbi efanele ukusetshenziswa. Abacacisi kufanele basebenzise ukucophelela ukuze bakhethe izinto ezifanele zokufaka amapayipi ukuze banciphise ingozi yokugqwala ngokusekelwe endaweni yokusebenza, izimo zenqubo kanye nezinye izinto eziguquguqukayo.
Ukuze kusizwe abacacisi ukuthi bathuthukise ukukhethwa kwezinto, bangaqhathanisa amanani e-PREN ezinsimbi ukuze banqume ukumelana kwazo nokugqwala kwendawo. I-PREN ingabalwa kusukela ekwakhiweni kwamakhemikhali kwe-alloy, okuhlanganisa okuqukethwe kwayo kwe-chromium (Cr), i-molybdenum (Mo), kanye ne-nitrogen (N), kanje:
I-PREN iyanda ngokuqukethwe kwezinto ezingamelani nokugqwala i-chromium, i-molybdenum kanye ne-nitrogen ku-alloy. Ubudlelwano be-PREN busekelwe ekushiseni okubalulekile kwe-pitting (CPT) - izinga lokushisa eliphansi kakhulu lapho kubonwa khona ukugqwala kwe-pitting - kwezinsimbi ezahlukene ezingagqwali maqondana nokwakheka kwamakhemikhali. Ngokuyisisekelo, i-PREN ilingana ne-CPT. Ngakho-ke, amanani aphezulu e-PREN abonisa ukumelana okuphezulu kwe-pitting. Ukwanda okuncane kwe-PREN kufana nokwanda okuncane kwe-CPT uma kuqhathaniswa ne-alloy, kanti ukwanda okukhulu kwe-PREN kubonisa ukuthuthuka okukhulu ekusebenzeni kuya ku-CPT ephezulu kakhulu.
Ithebula 1 liqhathanisa amanani e-PREN ezinhlobo ezahlukene ze-alloys ezivame ukusetshenziswa ekusetshenzisweni kukawoyela negesi ogwini lolwandle. Libonisa ukuthi imininingwane ingathuthukisa kanjani ukumelana nokugqwala ngokukhetha i-alloy yepayipi yezinga eliphezulu. I-PREN iyanda kancane kuphela uma ishintsha kusuka ku-316 kuya ku-317 insimbi engagqwali. Ukuze uthole ukwanda okukhulu kokusebenza, kungcono ukusebenzisa insimbi engagqwali engu-6 Mo super austenitic noma insimbi engagqwali engu-2507 super duplex.
Ukugxila okuphezulu kwe-nickel (Ni) ensimbini engagqwali nakho kuthuthukisa ukumelana nokugqwala. Kodwa-ke, okuqukethwe kwe-nickel ensimbini engagqwali akuyona ingxenye ye-PREN equation. Kunoma ikuphi, kuvame ukuba wusizo ukucacisa izinsimbi ezingagqwali ezinezinga eliphezulu le-nickel, njengoba lesi sakhi sisiza ukuphinda siguqule izindawo ezibonisa izimpawu zokugqwala kwendawo. I-nickel izinzisa i-austenite futhi ivimbele ukwakheka kwe-martensite lapho igoba noma idonsa ipayipi eliqinile elingu-1/8. I-Martensite iyisigaba sekristalu esingafuneki ezinsimbini esinciphisa ukumelana kwensimbi engagqwali nokugqwala kwendawo kanye nokuqhekeka kokucindezeleka okubangelwa yi-chloride. Okuqukethwe okuphezulu kwe-nickel okungenani okungu-12% ku-316/316L nakho kuyathandeka ekusetshenzisweni okubandakanya i-hydrogen yegesi enomfutho ophezulu. Ukugxila okuncane kwe-nickel okudingekayo ensimbini engagqwali engu-316/316L ku-ASTM standard specification kungu-10%.
Ukugqwala kwendawo kungenzeka noma kuphi emapayipini asetshenziswa ezindaweni zasolwandle. Kodwa-ke, ukugqwala kwemigodi kungenzeka kakhulu ezindaweni esezingcolisiwe kakade, kuyilapho ukugqwala kwemisele kungenzeka kakhulu ezindaweni ezinezikhala ezincane phakathi kwepayipi kanye nehadiwe yokufaka. Isebenzisa i-PREN njengesisekelo, isichazi singakhetha ingxube yepayipi engcono kakhulu ukunciphisa ingozi yanoma yiluphi uhlobo lokugqwala kwendawo.
Kodwa-ke, khumbula ukuthi kunezinye izinto ezingathinta ingozi yokugqwala. Isibonelo, izinga lokushisa lithinta ukumelana kwensimbi engagqwali nomgodi. Ezimweni zasemanzini ezishisayo, ipayipi lensimbi engagqwali elingu-6 molybdenum super austenitic noma ipayipi lensimbi engagqwali elingu-2507 super duplex kufanele licatshangelwe ngokungathi sína ngoba lezi zinto zinokumelana okuhle kakhulu nokugqwala kwendawo kanye nokuqhekeka kokucindezeleka kwe-chloride. Ezimweni ezipholile, ipayipi elingu-316/316L linganele, ikakhulukazi uma sekuvele umlando wokusetshenziswa ngempumelelo.
Abanikazi beplatifomu kanye nabaqhubi bangase bathathe izinyathelo zokunciphisa ingozi yokugqwala ngemva kokufakwa kwepayipi. Kufanele bagcine amapayipi ehlanzekile futhi ahlanzwe ngamanzi ahlanzekile njalo ukuze banciphise ingozi yokugqwala kwemigodi. Kufanele futhi babe nochwepheshe bokulungisa abavula ama-tube clamps ngesikhathi sokuhlolwa okuvamile ukuze babheke ukuthi kukhona ukugqwala kwemisele.
Ngokulandela izinyathelo ezichazwe ngenhla, abanikazi beplatifomu kanye nabaqhubi banganciphisa ingozi yokugqwala kwamapayipi kanye nokuvuza okuhlobene ezindaweni zasolwandle, bathuthukise ukuphepha nokusebenza kahle, ngenkathi benciphisa amathuba okulahleka komkhiqizo noma ukukhishwa kokukhishwa kwegesi okubalekayo.
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 ingumagazini ohamba phambili we-Society of Petroleum Engineers, enikeza izincazelo ezicacile nezici mayelana nentuthuko kwezobuchwepheshe bokuhlola nokukhiqiza, izindaba zemboni kawoyela negesi, kanye nezindaba mayelana ne-SPE namalungu ayo.