Nangona imibhobho yentsimbi engagqwaliyo inamandla okugqwala, imibhobho yentsimbi engagqwaliyo efakwe kwiindawo zaselwandle ichaphazeleka ziintlobo ezahlukeneyo zokugqwala ngexesha lomsebenzi wayo olindelekileyo. Oku kugqwala kunokukhokelela ekukhutshweni komoya okubalekayo, ukulahleka kwemveliso kunye neengozi ezinokubakho. Abanini beplatifomu zangaphandle kunye nabaqhubi banokunciphisa umngcipheko wokugqwala ngokuchaza izixhobo zepayipi ezinamandla kwasekuqaleni ukuze bamelane nokugqwala ngcono. Emva koko, kufuneka bahlale bephaphile xa behlola imigca yokufaka iikhemikhali, imigca ye-hydraulic kunye ne-impulse, kunye nezixhobo zokusebenza kunye nezixhobo ukuqinisekisa ukuba ukugqwala akusongeli ukuthembeka kwemibhobho efakiweyo okanye kubeke emngciphekweni ukhuseleko.
Ukugqwala kwendawo ethile kunokufumaneka kumaqonga amaninzi, kwiinqanawa, kwiinqanawa nakwiipayipi zaselwandle. Oku kugqwala kunokuba ngendlela yokugqwala kwemingxuma okanye imingxuma, nokuba yeyiphi na kwezi enokonakalisa udonga lombhobho kwaye ibangele ukuba kukhutshwe ulwelo.
Umngcipheko wokugqwala uyanda njengoko ubushushu bokusebenza kwesicelo busanda. Ubushushu bunokukhawulezisa ukuwohloka kwefilimu ye-oxide yangaphandle ekhuselayo yombhobho, ngaloo ndlela ikhuthaza ukuqhekeka.
Ngelishwa, ukugqwala kwemigodi kunye nemingxuma kwindawo ethile kunzima ukukubona, okwenza kube nzima ukuchonga, ukuqikelela, kunye nokuyila olu hlobo lokugqwala. Ngenxa yezi ngozi, abanini beqonga, abaqhubi kunye nabakhethiweyo kufuneka baqaphele ekukhetheni izinto zepayipi ezifanelekileyo zokusetyenziswa kwabo. Ukukhetha izinto yindlela yabo yokuqala yokuzikhusela ekugqwaleni, ngoko ke ukuyilungisa kubaluleke kakhulu. Ngethamsanqa, banokusebenzisa umlinganiselo olula kodwa osebenzayo kakhulu wokuxhathisa ukugqwala kwindawo ethile, iPitting Resistance Equivalent Number (PREN). Okukhona ixabiso lePREN lesinyithi liphezulu, kokukhona ukuxhathisa kwayo ukugqwala kwindawo ethile.
Eli nqaku liza kujonga indlela yokuchonga ukubola kwemingxuma kunye nemingxunya kunye nendlela yokuphucula ukukhethwa kwezinto zetyhubhu kwiindlela zeoyile kunye negesi ezisetyenziswa elwandle ngokusekelwe kwixabiso le-PREN yezixhobo.
Ukubola kwendawo kwenzeka kwiindawo ezincinci xa kuthelekiswa nokubola okuqhelekileyo, okufana ngakumbi phezu komphezulu wesinyithi. Ukubola kwe-pitting kunye ne-cravice kuqala ukwenzeka kwi-316 stainless steel tube xa ifilimu yangaphandle ye-chromium-rich passive oxide yesinyithi iqhekeka ngokuchatshazelwa zizinto ezibolayo, kuquka namanzi anetyuwa. Iindawo zaselwandle ezityebileyo kwiikloride, kunye namaqondo obushushu aphezulu kunye nongcoliseko lomphezulu wetyhubhu, kwandisa amathuba okuwohloka kwale filimu yokungaphazamisi.
ukugqwala kwemigodi Ukugqwala kwemigodi kwenzeka xa ifilimu yokuphambuka kwicandelo lombhobho iqhekeka, yenze imingxunya emincinci okanye imingxunya kumphezulu wombhobho. Imingxunya enjalo inokukhula njengoko ii-electrochemical reactions ziqhubeka, ngenxa yoko isinyithi esikwisinyithi sinyibilika kwisisombululo ezantsi komngxuma. Isinyithi esinyibilikisiweyo siya kuthi emva koko sisasazeke siye phezulu komngxuma size sinyibilike ukuze senze i-iron oxide okanye umhlwa. Njengoko umngxuma usiba nzulu, ii-electrochemical reactions ziyakhawuleza, ukugqwala kuyanda, okunokukhokelela ekugqobhozeni kodonga lombhobho kwaye kukhokelele ekuvuzeni.
Iityhubhu zisengozini enkulu yokutsalwa yimingxuma ukuba umphezulu wazo wangaphandle ungcolisiwe (Umfanekiso 1). Umzekelo, izinto ezingcolisayo ezivela kwimisebenzi yokudibanisa kunye nokugaya zingonakalisa umaleko we-passivation oxide wombhobho, ngaloo ndlela zenze kwaye zikhawulezise ukutsalwa kwemingxuma. Oku kuyafana nangokujongana nongcoliseko oluvela kwiipayipi. Ukongeza, njengoko amathontsi etyuwa ephuma, iikristale zetyuwa ezimanzi ezikwiipayipi zikhusela umaleko we-oxide kwaye zinokubangela ukutsalwa kwemingxuma. Ukuthintela olu hlobo longcoliseko, gcina iipayipi zakho zicocekile ngokuzihlamba rhoqo ngamanzi amatsha.
Umfanekiso 1. Umbhobho wentsimbi engagqwaliyo oyi-316/316L ongcoliswe yi-asidi, ityuwa, kunye nezinye izinto ezidityanisiweyo usengozini enkulu yokuhlaselwa yimingxuma.
ukubola kwe-crevice. Kwiimeko ezininzi, ukubola kwe-crevice kunokubonwa lula ngumsebenzisi. Nangona kunjalo, ukubola kwe-crevice akulula ukukubona kwaye kubeka umngcipheko omkhulu kubasebenzi nakubasebenzi. Oku kudla ngokuvela kwimibhobho enezikhewu ezincinci phakathi kwezinto ezijikelezileyo, njengemibhobho ebanjwe endaweni enezikhonkwane okanye imibhobho ehlanganiswe ngokuqinileyo ecaleni komnye nomnye. Xa i-brine ingena kwi-gap, ngokuhamba kwexesha, isisombululo se-ferric chloride esine-acidified acidified (FeCl3) senziwa kule ndawo, nto leyo ebangela ukubola okukhawulezileyo kwe-gap (Umzobo 2). Ekubeni ukubola kwe-crevice ngokwemvelo yayo kwandisa umngcipheko wokubola, ukubola kwe-crevice kunokwenzeka kumaqondo obushushu aphantsi kakhulu kune-pitting.
Umfanekiso 2 – Ukubola komngxuma kungakhula phakathi kombhobho kunye nenkxaso yombhobho (phezulu) kwaye xa umbhobho ufakwe kufutshane nezinye iindawo (ezantsi) ngenxa yokwenziwa kwesisombululo se-asidi esinoburhalarhume se-ferric chloride kwisikhewu.
Ukubola kwe-crevice kudla ngokufana nokugrumba kwe-pipe kuqala kwindawo ephakathi kwecandelo lombhobho kunye nekhola yokuxhasa umbhobho. Nangona kunjalo, ngenxa yokwanda koxinzelelo lwe-Fe++ kulwelo olungaphakathi kwe-fracture, i-funnel yokuqala iba nkulu kwaye ibe nkulu ide igubungele yonke i-fracture. Ekugqibeleni, ukubola kwe-crevice kunokukhokelela ekugqobhokeni kombhobho.
Iimfanta ezixineneyo zingumngcipheko omkhulu wokugqwala. Ke ngoko, ii-clamps zepayipi ezijikeleza inxalenye enkulu yomjikelezo wombhobho zihlala zinobungozi ngaphezu kwee-clamps ezivulekileyo, ezinciphisa umphezulu wokudibana phakathi kombhobho kunye ne-clamp. Iingcali zenkonzo zinokunceda ukunciphisa amathuba okonakala okanye ukungaphumeleli kokugqwala ngokuvula rhoqo izixhobo kunye nokuhlola iindawo zepayipi ukuba azigqwali na.
Ukugqwala kwe-pitting kunye ne-cravice kunokuthintelwa ngokukhetha i-alloy yesinyithi efanelekileyo yokusetyenziswa kwayo. Abachazi-magama kufuneka basebenzise unonophelo olufanelekileyo ekukhetheni izixhobo ezifanelekileyo zombhobho ukunciphisa umngcipheko wokugqwala, kuxhomekeke kwindawo yokusebenza, iimeko zenkqubo, kunye nezinye izinto eziguquguqukayo.
Ukunceda abachazi-magama baphucule ukhetho lwabo lwezinto, banokuthelekisa amaxabiso e-PREN eentsimbi ukuze babone ukumelana kwazo nokugqwala kwendawo. I-PREN ingabalwa kwikhemistri ye-alloy, kuquka i-chromium (Cr) yayo, i-molybdenum (Mo), kunye nomxholo we-nitrogen (N), ngolu hlobo lulandelayo:
I-PREN iyanda ngomxholo wezinto ezimelana nokugqwala ze-chromium, i-molybdenum kunye ne-nitrogen kwi-alloy. Umlinganiselo we-PREN usekelwe kubushushu obubalulekileyo be-pitting (CPT) - ubushushu obuphantsi apho i-pitting yenzeka khona - kwiintsimbi ezahlukeneyo ezingenasici kuxhomekeke kulwakhiwo lweekhemikhali. Ngokusisiseko, 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 kune-CPT ephezulu kakhulu.
Itheyibhile 1 ithelekisa amaxabiso e-PREN kwii-alloys ezahlukeneyo ezisetyenziswa rhoqo kushishino lweoyile negesi oluselunxwemeni. Ibonisa indlela iinkcukacha ezinokuphucula ngayo ukumelana nokugqwala ngokukhetha i-alloy yombhobho ekumgangatho ophezulu. I-PREN inyuka kancinci ukusuka kwi-316 SS ukuya kwi-317 SS. I-Super Austenitic 6 Mo SS okanye i-Super Duplex 2507 SS zilungele ukuzuza okukhulu kokusebenza.
Amanqanaba aphezulu e-nickel (Ni) kwintsimbi engagqwaliyo nawo anyusa ukumelana nokugqwala. Nangona kunjalo, umxholo we-nickel kwintsimbi engagqwaliyo awuyonxalenye ye-PREN equation. Nokuba kunjalo, kudla ngokuba luncedo ukukhetha iintsimbi ezingagqwaliyo ezinomxholo ophezulu we-nickel, njengoko le nto inceda ekubuyiseleni imiphezulu ebonisa iimpawu zokugqwala kwendawo. I-nickel izinzisa i-austenite kwaye ithintela ukwakheka kwe-martensite xa igoba okanye itsala umbhobho oqinileyo we-1/8. I-Martensite sisigaba sekristale esingafunekiyo kwiintsimbi esinciphisa ukumelana kwentsimbi engagqwaliyo ekugqwaleni kwendawo kunye nokuqhekeka koxinzelelo olubangelwa yi-chloride. Umxholo ophezulu we-nickel ubuncinane we-12% kwintsimbi ye-316/316L ukwayimfuneko kwizicelo zegesi ye-hydrogen enoxinzelelo oluphezulu. Uxinzelelo oluncinci lwe-nickel olufunekayo kwintsimbi engagqwaliyo ye-ASTM 316/316L yi-10%.
Ukugqwala kwendawo kunokwenzeka naphi na kumbhobho osetyenziswa kwindawo yaselwandle. Nangona kunjalo, ukugqwala kwendawo kunokwenzeka kakhulu kwiindawo ezisele zingcolisiwe, ngelixa ukugqwala kwemingxuma kunokwenzeka kakhulu kwiindawo ezinezikhewu ezincinci phakathi kombhobho nezixhobo zokufakela. Isebenzisa i-PREN njengesiseko, i-specifier inokukhetha umgangatho olungileyo wombhobho ukunciphisa umngcipheko walo naluphi na uhlobo lokugqwala kwendawo.
Nangona kunjalo, khumbula ukuba kukho ezinye izinto ezinokuthi zichaphazele umngcipheko wokugqwala. Umzekelo, ubushushu buchaphazela ukumelana kwentsimbi engagqwaliyo nemingxuma. Kwiimozulu ezishushu zaselwandle, iipayipi zentsimbi engagqwaliyo ze-super austenitic 6 molybdenum okanye ze-super duplex 2507 kufuneka ziqwalaselwe nzulu kuba ezi zinto zinokumelana okuhle kakhulu nokugqwala kwendawo kunye nokuqhekeka kwe-chloride. Kwiimozulu ezipholileyo, ipayipi ye-316/316L inokwanela, ingakumbi ukuba kukho imbali yokusetyenziswa ngempumelelo.
Abanini beeplatifomu zamanzi angaphandle kunye nabaqhubi bangathatha amanyathelo okunciphisa umngcipheko wokugqwala emva kokuba iityhubhu zifakiwe. Bafanele bagcine imibhobho icocekile kwaye ihlanjwe rhoqo ngamanzi acocekileyo ukunciphisa umngcipheko wokugqwala. Bafanele babe neengcali zokulungisa ezivula ii-clamps ngexesha lokuhlolwa rhoqo ukujonga ukugqwala kwemiqolo.
Ngokulandela la manyathelo angasentla, abanini beqonga kunye nabaqhubi banokunciphisa umngcipheko wokugqwala kwemibhobho kunye nokuvuza okunxulumene noko kwindawo yolwandle, baphucule ukhuseleko kunye nokusebenza kakuhle, kwaye banciphise amathuba okulahleka kwemveliso okanye ukukhutshwa komoya ongcolileyo.
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, ijenali ephambili ye-Society of Petroleum Engineers, inika amagqabaza asemthethweni kunye namanqaku malunga nokuqhubela phambili kwezobuchwepheshe obuphezulu, imiba yeshishini leoyile negesi, kunye neendaba malunga ne-SPE kunye namalungu ayo.