Naphezu kokumelana nokugqwala okungokwemvelo kwamapayipi ensimbi engagqwali, amapayipi ensimbi engagqwali afakwe ezindaweni zasolwandle angaphansi kwezinhlobo ezihlukahlukene zokugqwala phakathi nokuphila kwawo kwesevisi okulindelekile.Lokhu kugqwala kungaholela ekukhiqizweni okungabaleki, ukulahleka kwemikhiqizo kanye nezingozi ezingaba khona.Abanikazi benkundla yasolwandle kanye nabaqhubi banganciphisa ingozi yokugqwala ngokucacisa izinto zamapayipi ezinamandla ezinikeza ukumelana nokugqwala okungcono.Ngemva kwalokho, kufanele bahlale beqaphile lapho behlola imigqa yokujova amakhemikhali, imigqa yokudonsa amanzi kanye ne-impulse, futhi bacubungule izinsimbi nezinsimbi ukuze baqinisekise ukuthi ukugqwala akuphazamisi ubuqotho bamapayipi afakiwe noma ukuphepha engozini.
Ukugqwala kwendawo kungatholakala ezinkundleni eziningi, emikhunjini, emikhunjini nakumapayipi asogwini.Lokhu kugqwala kungaba ngendlela yomgodi noma ukugqwala kwemifantu, noma yikuphi okungaguguleka udonga lwamapayipi futhi kubangele ukuthi kuphume uketshezi.
Ingozi yokugqwala iyanda njengoba izinga lokushisa lokusebenza likhuphuka.Ukushisa kungasheshisa ukuwohloka kwefilimu yeshubhu ye-passive oxide yangaphandle evikelayo, ngaleyo ndlela kuthuthukise umgodi.
Ngeshwa, i-pitting yendawo kanye nokugqwala kwemifantu kunzima ukukubona, okwenza kube nzima ukuhlonza, ukubikezela, nokuklama lezi zinhlobo zokugqwala.Uma kubhekwa lobu bungozi, abanikazi bezinkundla, opharetha nabaqokiwe kufanele baqaphele ekukhetheni okubalulekile okuhamba phambili kwamapayipi abazokusebenzisa.Ukukhetha okubalulekile kuwumugqa wabo wokuqala wokuzivikela ekugqwaleni, ngakho ukukulungisa kubaluleke kakhulu.Ngenhlanhla, bangakhetha isilinganiso esilula kodwa esisebenza kahle kakhulu sokumelana nokugqwala kwendawo, Inombolo Elinganayo Yokumelana Ne-Pitting (PREN).Uma liphakeme inani le-PREN lensimbi, liphakamisa ukumelana kwayo nokugqwala kwendawo.
Lesi sihloko sizobheka indlela yokuhlonza ukugqwala kwe-pitting kanye ne-crevice, kanye nendlela yokuthuthukisa ukukhethwa kwezinto zamashubhu ku-offshore oil ne-gas applications ngokusekelwe kunani le-PREN lempahla.
Ukugqwala kwendawo kwenzeka ezindaweni ezincane uma kuqhathaniswa nokugqwala okuvamile, okufana kakhulu endaweni yensimbi.Ukugqwala kwemigodi nokuqhekeka kuqala ukwakheka kushubhu lensimbi engagqwali engu-316 lapho ifilimu yangaphandle ye-chromium ye-passive oxide yensimbi iphuka ngenxa yokuchayeka oketshezini olubolayo, okuhlanganisa namanzi anosawoti.Izindawo zasolwandle ezicebile ngama-chloride, kanye namazinga okushisa aphezulu ngisho nokungcoliswa kwendawo yamashubhu, kwandisa amathuba okucekelwa phansi kwaleli filimu lokudlula.
I-pitting Ukugqwala kwe-pitting kwenzeka lapho ifilimu ye-passivation engxenyeni yepayipi iphuka, yakhe imigodi emincane noma imigodi ebusweni bepayipi.Imigodi enjalo ingase ikhule njengoba ukusabela kwe-electrochemical kuqhubeka, ngenxa yalokho insimbi esensimbi incibilika ibe yisixazululo ngaphansi komgodi.Insimbi encibilikisiwe izobe isisakazekela phezulu emgodini bese i-oxidize yakhe i-iron oxide noma ukugqwala.Njengoba umgodi ujula, ukusabela kwe-electrochemical kuyashesha, ukugqwala kuyanda, okungaholela ekubhobokeni kodonga lwamapayipi futhi kuholele ekuvuzeni.
Amashubhu asengozini yokubhoboza uma ingaphandle lawo lingcolile (Umfanekiso 1).Isibonelo, ukungcola okuvela ekusebenzeni kwe-welding nokugaya kungalimaza ungqimba lwe-passivation oxide yepayipi, ngaleyo ndlela kwakheka futhi kusheshise umgodi.Okufanayo kuya nangokubhekana nokungcoliswa kwamapayipi.Ngaphezu kwalokho, njengoba amaconsi kasawoti ehwamuka, amakristalu kasawoti amanzi akheka emapayipini avikela ungqimba lwe-oxide futhi angaholela emigodini.Ukuze uvimbele lezi zinhlobo zokungcola, gcina amapayipi akho ehlanzekile ngokuwageza njalo ngamanzi ahlanzekile.
Umfanekiso 1. 316/316L ipayipi lensimbi engagqwali elingcoliswe i-asidi, i-saline, nezinye izinto ezifakwayo kulula kakhulu ukuba zibe nemigodi.
ukugqwala kwe-crevice.Ezimweni eziningi, umgodi ungabonwa kalula ngu-opharetha.Kodwa-ke, ukugqwala kwemifantu akulula ukukubona futhi kubangela ingozi enkulu kubaqhubi nakubasebenzi.Lokhu kuvame ukwenzeka kumapayipi anezikhala eziwumngcingo phakathi kwezinto ezizungezile, njengamapayipi abanjwe endaweni enezinsimbi noma amapayipi ahlanganiswe ngokuqinile eduze kwelinye.Lapho amanzi anosawoti angena emfantwini, ngokuhamba kwesikhathi, kwakheka ingxube ye-acidified ferric chloride solution (FeCl3) enekhemikhali kule ndawo, edala ukugqwala kwe-crevice kusheshise (Fig. 2).Njengoba uqhekeko ngokwalo lwandisa ingozi yokugqwala, ukugqwala kwemigodi kungenzeka emazingeni okushisa aphansi kakhulu kunomgodi.
Umfanekiso wesi-2 - Ukugqwala kwe-Crevice kungakhula phakathi kwepayipi kanye nokusekela ipayipi (phezulu) futhi uma ipayipi lifakwe eduze kwezinye izindawo (ngezansi) ngenxa yokwakheka kwesisombululo esinolaka samakhemikhali se-ferric chloride esikhaleni.
Ukugqwala kwe-Crevice ngokuvamile kulingisa ukugoba kuqala esikhaleni esakhiwe phakathi kwengxenye yamapayipi nokhololo lokusekela amapayipi.Kodwa-ke, ngenxa yokwanda kokuhlushwa kwe-Fe ++ oketshezini olungaphakathi kwe-fracture, ifaneli yokuqala iba nkulu futhi ibe nkulu ize ihlanganise konke ukuphuka.Ekugcineni, ukugqwala komfantu kungaholela ekubhobokeni kwepayipi.
Imifantu eminyene imelela ingozi enkulu yokugqwala.Ngakho-ke, izinsimbi zamapayipi ezizungeza ingxenye enkulu yesiyingi sepayipi zivamise ukuba yingozi kakhulu kunezinsimbi ezivulekile, ezinciphisa indawo yokuxhumana phakathi kwepayipi ne-clamp.Ochwepheshe besevisi bangasiza ekunciphiseni amathuba okulimala kokugqwala kwemifantu noma ukwehluleka ngokuvula ama-clamp njalo futhi bahlole indawo yamapayipi ukugqwala.
Ukugqwala kwemigodi nokuqhekeka kungavinjelwa ngokukhetha ingxubevange yensimbi efanele yohlelo lokusebenza.Abacacisi kufanele basebenzise ukucophelela ekukhetheni okubalulekile kwamapayipi ukuze kuncishiswe ubungozi bokugqwala kuye ngendawo yenqubo, izimo zenqubo, nokunye okuhlukile.
Ukusiza izicacisi ukuthi zilungiselele ukukhetha kwezinto ezibonakalayo, zingaqhathanisa amanani e-PREN ezinsimbi ukuze zinqume ukumelana kwazo nokugqwala kwendawo.I-PREN ingabalwa kukhemistri yealloy, okuhlanganisa ne-chromium (Cr), i-molybdenum (Mo), ne-nitrogen (N) okuqukethwe, kanje:
I-PREN iyanda ngokuqukethwe kwezinto ezimelana nokugqwala ze-chromium, i-molybdenum ne-nitrogen ku-alloy.Isilinganiso se-PREN sisekelwe ekushiseni okubalulekile kwe-pitting (CPT) - izinga lokushisa eliphansi kakhulu lapho ukugoba kwenzeka khona - ezinsimbi ezihlukahlukene ezingenasici kuye ngokwakhiwa kwamakhemikhali.Empeleni, i-PREN ilingana ne-CPT.Ngakho-ke, amanani aphezulu e-PREN akhombisa ukumelana nokugoba okuphezulu.Ukwanda okuncane kwe-PREN kulingana kuphela nokunyuka okuncane kwe-CPT uma kuqhathaniswa ne-alloy, kuyilapho ukwanda okukhulu kwe-PREN kubonisa ukuthuthukiswa okuphawulekayo ekusebenzeni ngaphezu kwe-CPT ephakeme kakhulu.
Ithebula 1 liqhathanisa amanani e-PREN ama-alloys ahlukahlukene avame ukusetshenziswa embonini kawoyela negesi yasolwandle.Ibonisa ukuthi ukucaciswa kungathuthukisa kanjani kakhulu ukumelana nokugqwala ngokukhetha ingxubevange yepayipi yekhwalithi ephezulu.I-PREN ikhuphuka kancane isuka ku-316 SS iye ku-317 SS.I-Super Austenitic 6 Mo SS noma i-Super Duplex 2507 SS ilungele ukukhuphuka okuphawulekayo kokusebenza.
Ukugxila kwe-nickel ephakeme (Ni) kunsimbi engagqwali nakho kukhulisa ukumelana nokugqwala.Kodwa-ke, okuqukethwe kwe-nickel yensimbi engagqwali akuyona ingxenye yezibalo ze-PREN.Kunoma yikuphi, ngokuvamile kunenzuzo ukukhetha izinsimbi ezingenasici ezinokuqukethwe okuphezulu kwe-nickel, njengoba lesi sakhi sisiza ukuphinda kudlule izindawo ezibonisa izimpawu zokugqwala kwendawo.I-Nickel iqinisa i-austenite futhi ivimbela ukwakheka kwe-martensite lapho igoba noma ibanda idweba ipayipi elingu-1/8 eliqinile.I-Martensite iyisigaba sekristalu esingathandeki ezinsimbi esinciphisa ukumelana kwensimbi engagqwali ekugqwaleni kwendawo kanye nokuqhekeka kwengcindezi okubangwa yi-chloride.Okuqukethwe kwe-nickel ephakeme okungenani okungu-12% ku-316/316L yensimbi nakho kuyafiseleka ekufakweni kwegesi ye-hydrogen enengcindezi ephezulu.Isilinganiso esincane se-nickel esidingekayo ku-ASTM 316/316L yensimbi engagqwali ngu-10%.
Ukugqwala kwasendaweni kungenzeka noma kuphi kumapayipi asetshenziswa ezindaweni zasolwandle.Kodwa-ke, ukugqwala kungenzeka kakhulu ezindaweni esezingcolisiwe kakade, kuyilapho ukugqwala kwemigodi kungenzeka kakhulu ezindaweni ezinezikhala ezincane phakathi kwepayipi nempahla yokufaka.Ngokusebenzisa i-PREN njengesisekelo, isicacisi singakhetha ingxubevange yamapayipi engcono kakhulu ukuze kuncishiswe ubungozi banoma yiluphi uhlobo lokugqwala kwendawo.
Kodwa-ke, khumbula ukuthi kunezinye izinto eziguquguqukayo ezingathinta ubungozi bokugqwala.Isibonelo, izinga lokushisa lithinta ukumelana kwensimbi engagqwali emigodini.Ezimweni ezishisayo zasolwandle, i-super austenitic 6 molybdenum steel noma i-super duplex 2507 yamapayipi ensimbi engagqwali kufanele kubhekwe ngokujulile njengoba lezi zinto zikwazi ukumelana kahle nokugqwala kwendawo kanye nokuqhekeka kwe-chloride.Ezimweni ezipholile, ipayipi elingu-316/316L lingase lanele, ikakhulukazi uma kunomlando wokusetshenziswa ngempumelelo.
Abanikazi benkundla yasolwandle kanye nabaqhubi bangakwazi futhi ukuthatha izinyathelo zokunciphisa ubungozi bokugqwala ngemva kokufakwa kweshubhu.Kufanele bagcine amapayipi ehlanzekile futhi njalo egezwa ngamanzi ahlanzekile ukuze kuncishiswe ingozi yokubhoboza.Kufanele futhi babe nochwepheshe bezokulungisa abavula izinsimbi zamapayipi ngesikhathi sokuhlolwa okujwayelekile ukuze bahlole ukugqwala kwemifantu.
Ngokulandela izinyathelo ezingenhla, abanikazi benkundla nabaqhubi banganciphisa ingcuphe yokugqwala kwamapayipi nokuvuza okuhlobene endaweni yasolwandle, bathuthukise ukuphepha nokusebenza kahle, futhi banciphise ithuba lokulahleka 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 iyijenali ehamba phambili yeNhlangano Yonjiniyela Bezokwakha, enezifinyezo ezigunyaziwe nama-athikili mayelana nenqubekelaphambili kubuchwepheshe obukhuphukayo, izindaba zemboni kawoyela negesi, kanye nezindaba ezimayelana ne-SPE namalungu ayo.