Naphezu kokumelana nokugqwala okungokwemvelo kwamapayipi ensimbi engagqwali, amapayipi ensimbi engagqwali afakwe ezindaweni zasolwandle abhekene nezinhlobo ezahlukene zokugqwala ngesikhathi sokuphila kwawo okulindelekile. Lokhu kugqwala kungaholela ekukhishweni komoya okubalekayo, ukulahlekelwa kwemikhiqizo kanye nezingozi ezingaba khona. Abanikazi beplatifomu kanye nabaqhubi basogwini banganciphisa ingozi yokugqwala ngokuchaza izinto zepayipi eziqinile ezinikeza ukumelana nokugqwala okungcono. Ngemva kwalokho, kumele bahlale beqaphile lapho behlola imigqa yokujova ngamakhemikhali, imigqa ye-hydraulic kanye ne-impulse, kanye nokucubungula izinsimbi kanye nezinsimbi ukuqinisekisa ukuthi ukugqwala akusongeli ubuqotho bamapayipi afakiwe noma kubeke engcupheni ukuphepha.
Ukugqwala kwendawo kungatholakala ezinkundleni eziningi, emikhunjini, emikhunjini nasemapayipini asogwini lolwandle. Lokhu kugqwala kungaba ngesimo sokugqwala kwemigodi noma i-crevice, okungaguguleka udonga lwepayipi futhi kubangele uketshezi lukhishwe.
Ingozi yokugqwala iyanda njengoba izinga lokushisa lokusebenza kwesicelo likhuphuka. Ukushisa kungasheshisa ukuwohloka kwefilimu yangaphandle ye-passive oxide evikelayo yethubhu, ngaleyo ndlela kukhuthaze ukugoba.
Ngeshwa, ukugqwala kwemigodi yendawo kanye nemigodi kunzima ukukubona, okwenza kube nzima ukuhlonza, ukubikezela, kanye nokuklama lezi zinhlobo zokugqwala. Ngenxa yalezi zingozi, abanikazi beplatifomu, abaqhubi kanye nabaqokiwe kumele baqaphele ekukhetheni izinto zombhobho ezingcono kakhulu zokusetshenziswa kwabo. Ukukhetha izinto kuyindlela yabo yokuqala yokuzivikela ekugqwaleni, ngakho-ke ukwenza kahle kubaluleke kakhulu. Ngenhlanhla, bangakhetha isilinganiso esilula kakhulu 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 sizobheka 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 phezu kobuso bensimbi. Ukugqwala kwe-pitting kanye ne-crevice kuqala ukwakheka kumapayipi ensimbi angagqwali angu-316 lapho ifilimu yangaphandle yensimbi ecebile nge-chromium e-passive oxide iphuka ngenxa yokuchayeka kuketshezi olugqwalisayo, okuhlanganisa namanzi anosawoti. Izindawo zasolwandle ezicebile ngama-chloride, kanye namazinga okushisa aphezulu ngisho nokungcoliswa kobuso bamapayipi, kwandisa amathuba okuwohloka kwale filimu yokudlula.
ukugqwala kwemigodi Ukugqwala kwemigodi kwenzeka lapho ifilimu yokudlulisa engxenyeni yepayipi iphuka, yakha imigodi emincane noma imigodi ebusweni bepayipi. Imigodi enjalo cishe izokhula njengoba ukusabela kwe-electrochemical kuqhubeka, ngenxa yalokho insimbi ensimbini incibilika esixazululweni 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 kuyanda, okungaholela ekubhobokeni kodonga lwepayipi futhi kuholele ekuvuza.
Amapayipi asengozini enkulu yokufakwa kwemigodi uma indawo yawo yangaphandle ingcolile (Isithombe 1). Isibonelo, ukungcola okuvela emisebenzini yokushisela nokugaya kungalimaza ungqimba lwe-passivation oxide lwepayipi, ngaleyo ndlela kwakheke futhi kusheshise ukufakwa kwemigodi. Kungokufanayo nangokubhekana nokungcola okuvela emapayipini. Ngaphezu kwalokho, njengoba amaconsi kasawoti ehwamuka, amakristalu kasawoti amanzi akheka emapayipini avikela ungqimba lwe-oxide futhi angaholela ekufakweni kwemigodi. Ukuze uvimbele lolu hlobo lokungcola, gcina amapayipi akho ehlanzekile ngokuwageza njalo ngamanzi ahlanzekile.
Umfanekiso 1. Ipayipi lensimbi engagqwali elingu-316/316L elingcoliswe yi-asidi, usawoti, kanye nezinye izinto ezididayo lisengozini enkulu yokufakwa kwemigodi.
ukugqwala komchopho. Ezimweni eziningi, ukugqwala komchopho kungatholakala kalula ngumsebenzisi. Kodwa-ke, ukugqwala komchopho akulula ukukubona futhi kubeka ingozi enkulu kubasebenzi nakubasebenzi. Lokhu kuvame ukwenzeka emapayipini anezikhala ezincane phakathi kwezinto ezizungezile, njengepayipi elibanjwe endaweni enezibambo noma amapayipi ahlanganiswe ngokuqinile eduze komunye nomunye. Lapho i-brine ingena emchophoni, ngokuhamba kwesikhathi, kwakheka isixazululo se-ferric chloride (FeCl3) esinamandla ngamakhemikhali kule ndawo, okubangela ukugqwala komchopho ukuthi kusheshise (Isithombe 2). Njengoba umchopho ngokwawo ukhulisa ingozi yokugqwala, ukugqwala komchopho kungenzeka emazingeni okushisa aphansi kakhulu kune-pitting.
Umfanekiso 2 – Ukugqwala komgodi kungakheka phakathi kwepayipi kanye nokusekelwa kwepayipi (phezulu) nalapho ipayipi lifakwe eduze kwezinye izindawo (phansi) ngenxa yokwakheka kwesisombululo se-ferric chloride esinolaka ngamakhemikhali esikhaleni.
Ukugqwala kwe-crevice kuvame ukulingisa ukubhoboka kwemigodi kuqala esikhaleni esakhiwe phakathi kwesigaba sepayipi kanye nekhola yokusekela ipayipi. Kodwa-ke, ngenxa yokwanda kokuhlushwa kwe-Fe++ oketshezini olungaphakathi kwe-fracture, i-funnel yokuqala iba nkulu futhi ibe nkulu kuze kube yilapho imboza yonke i-fracture. Ekugcineni, ukugqwala kwe-crevice kungaholela ekubhobokeni kwepayipi.
Imifantu emikhulu imelela ingozi enkulu yokugqwala. Ngakho-ke, izibambo zamapayipi ezizungeze ingxenye enkulu yomjikelezo wepayipi zivame ukuba yingozi kakhulu kunezibambo ezivulekile, ezinciphisa indawo yokuxhumana phakathi kwepayipi nesibambo. Ochwepheshe bezinsizakalo bangasiza ekunciphiseni amathuba okulimala noma ukwehluleka kokugqwala ngokuvula izibambo njalo nokuhlola indawo yepayipi ukuthi ayigqwali yini.
Ukugqwala kwe-pitting kanye ne-crevice kungavinjelwa ngokukhetha i-alloy yensimbi efanele yokusetshenziswa. Abacacisi kumele basebenzise ukucophelela ekukhetheni izinto ezifanele zokufaka amapayipi ukuze banciphise ingozi yokugqwala kuye ngendawo yenqubo, izimo zenqubo, 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 kumakhemikhali e-alloy, okuhlanganisa okuqukethwe kwayo kwe-chromium (Cr), i-molybdenum (Mo), kanye ne-nitrogen (N), kanje:
I-PREN iyanda ngokuqukethwe kwezinto ezingamelani nokugqwala ze-chromium, i-molybdenum kanye ne-nitrogen ku-alloy. Isilinganiso se-PREN sisekelwe ekushiseni okubalulekile kwe-pitting (CPT) - izinga lokushisa eliphansi kakhulu lapho kwenzeka khona i-pitting - kwezinsimbi ezahlukene ezingagqwali kuye ngokwakheka kwamakhemikhali. Empeleni, 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, kuyilapho ukwanda okukhulu kwe-PREN kubonisa ukuthuthuka okukhulu ekusebenzeni ngaphezu kwe-CPT ephezulu kakhulu.
Ithebula 1 liqhathanisa amanani e-PREN ezinhlobo ezahlukene ze-alloys ezivame ukusetshenziswa embonini kawoyela negesi yasogwini. Libonisa ukuthi imininingwane ingathuthukisa kanjani ukumelana nokugqwala ngokukhetha i-alloy yepayipi esezingeni eliphezulu. I-PREN ikhula kancane kusuka ku-316 SS kuya ku-317 SS. I-Super Austenitic 6 Mo SS noma i-Super Duplex 2507 SS zilungele ukwanda okukhulu kokusebenza.
Ukugcwala okuphezulu kwe-nickel (Ni) ensimbini engagqwali nakho kwandisa ukumelana nokugqwala. Kodwa-ke, okuqukethwe kwe-nickel kwensimbi engagqwali akuyona ingxenye ye-PREN equation. Kunoma ikuphi, kuvame ukuba nenzuzo ukukhetha izinsimbi ezingagqwali ezinokuqukethwe okuphezulu kwe-nickel, njengoba lesi sakhi sisiza ukuphinda siguqule izindawo ezibonisa izimpawu zokugqwala kwendawo. I-nickel izinzisa i-austenite futhi ivimbela ukwakheka kwe-martensite lapho igoba noma idonsa ipayipi eliqinile elingu-1/8. I-Martensite iyisigaba sekristalu esingafuneki ezinsimbini esinciphisa ukumelana kwensimbi engagqwali ekugqwaleni kwendawo kanye nokuqhekeka kokucindezeleka okubangelwa yi-chloride. Okuqukethwe okuphezulu kwe-nickel okungenani okungu-12% ensimbini engu-316/316L nakho kuyathandeka ekusetshenzisweni kwegesi ye-hydrogen enomfutho ophezulu. Ukugcwala okuncane kwe-nickel okudingekayo ensimbini engagqwali ye-ASTM 316/316L 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 nemishini yokufaka. Isebenzisa i-PREN njengesisekelo, i-specifier ingakhetha i-alloy 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 ne-pitting. Ezimweni ezishisayo zasemanzini, amapayipi ensimbi angagqwali e-super austenitic 6 molybdenum noma amapayipi ensimbi angagqwali e-super duplex 2507 kufanele acatshangelwe ngokungathi sína njengoba lezi zinto zinokumelana okuhle kakhulu nokugqwala kwendawo kanye nokuqhekeka kwe-chloride. Ezimweni ezipholile, ipayipi elingu-316/316L linganele, ikakhulukazi uma kunomlando wokusetshenziswa ngempumelelo.
Abanikazi beplatifomu kanye nabaqhubi bangase bathathe izinyathelo zokunciphisa ingozi yokugqwala ngemva kokufakwa kwamapayipi. Kufanele bagcine amapayipi ehlanzekile futhi ehlanzwa njalo ngamanzi ahlanzekile ukuze banciphise ingozi yokuqhekeka kwemigodi. Kufanele futhi babe nochwepheshe bokulungisa abavula ama-clamp amapayipi ngesikhathi sokuhlolwa okuvamile ukuze bahlole ukugqwala kwemifantu.
Ngokulandela izinyathelo ezingenhla, abanikazi beplatifomu kanye nabaqhubi banganciphisa ingozi yokugqwala kwamapayipi kanye nokuvuza okuhlobene nendawo yasolwandle, bathuthukise ukuphepha nokusebenza kahle, futhi banciphise amathuba okulahleka komkhiqizo noma ukukhishwa kwegesi okubalekayo.
Brad Bollinger is the Oil and Gas Marketing Manager for Swagelok. He can be contacted at bradley.bollinger@swagelok.com.
I-Journal of Petroleum Technology iyiphephabhuku elihamba phambili le-Society of Petroleum Engineers, eliqukethe izifinyezo ezigunyaziwe kanye nezihloko mayelana nentuthuko kwezobuchwepheshe obuphezulu, izindaba zemboni kawoyela negesi, kanye nezindaba mayelana ne-SPE namalungu ayo.