Nangona kukho ukuxhathisa kwemvelo kwimibhobho yensimbi engenasici, imibhobho yensimbi engenasici efakwe kwiindawo zaselwandle ixhomekeke kwiindidi ezahlukeneyo zokubola ngexesha lokuphila kwabo okulindelweyo.Lo mhlwa unokukhokelela ekukhutshweni kwezinto ezikhutshwayo, ilahleko yemveliso kunye nemingcipheko enokubakho.Abanini beqonga le-Offshore kunye nabaqhubi banokunciphisa umngcipheko wokuduka ngokucacisa izixhobo zombhobho ezomeleleyo kwasekuqaleni ukwenzela ukumelana nokudumba okungcono.Emva koko, kufuneka bahlale bephaphile xa behlola imigca yokutofa kweekhemikhali, imigca ye-hydraulic kunye ne-impulse, kunye nenkqubo ye-instrumentation kunye ne-instrumentation ukuqinisekisa ukuba i-corrosion ayisongeli isidima sombhobho ofakelweyo okanye ukhuseleko oluhambelanayo.
Ukonakala kwendawo kunokufumaneka kumaqonga amaninzi, iinqanawa, iinqanawa kunye nemibhobho engaselunxwemeni.Lo mhlwa unokuba kwimo yemingxuma okanye kwimingxuma, nokuba yeyiphi enokukhukulisa udonga lombhobho kwaye ibangele ukuba kukhululwe ulwelo.
Umngcipheko wokubola uyanda njengoko ubushushu bokusebenza kwesicelo sanda.Ubushushu bunokukhawulezisa ukuthotywa kwefilimu yetyhubhu ekhuselayo ye-passive oxide yangaphandle, ngaloo ndlela ikhuthaza ukugqobhoza.
Ngelishwa, i-pitting yendawo kunye ne-corrosion ye-crevice kunzima ukuyibona, okwenza kube nzima ukuchonga, ukuqikelela, kunye nokuyila ezi ntlobo zomhlwa.Ngenxa yale mingcipheko, abanini bamaqonga, abaqhubi kunye nabatyunjiweyo kufuneka balumke xa bekhetha ezona mathiriyeli zibalaseleyo zombhobho kwisicelo sabo.Ukukhethwa kwezinto eziphathekayo ngumgca wabo wokuqala wokukhusela kwi-corrosion, ngoko ukuyilungisa kubaluleke kakhulu.Ngethamsanqa, banokusebenzisa umlinganiselo olula kakhulu kodwa osebenzayo kakhulu wokumelana ne-corrosion yendawo, i-Pitting Resistance Equivalent Number (PREN).Ukuphakama kwexabiso le-PREN lesinyithi, liphezulu ukuchasana kwayo kwi-corrosion yendawo.
Eli nqaku liza kujonga indlela yokuchonga i-pitting kunye ne-crevice corrosion kunye nendlela yokuphucula ukhetho lwe-tubing ye-oyile ye-offshore kunye ne-gas applications ngokusekelwe kwixabiso le-PREN.
I-corrosion yendawo yenzeke kwiindawo ezincinci xa kuthelekiswa ne-corrosion jikelele, eyona nto ifanayo ngaphezu komphezulu wesinyithi.I-Pitting kunye ne-crevice corrosion iqala ukuvela kwi-316 yensimbi engenasici xa ifilimu yangaphandle ye-chromium etyebileyo ye-oxide yesinyithi igqabhuka kukuchanabeka kulwelo oludlekayo, kubandakanywa namanzi anetyuwa.Iindawo zaselwandle ezityebileyo kwiikloridi, kunye namaqondo obushushu aphezulu kunye nokungcoliseka komphezulu wetyhubhu, zonyusa amathuba okuthotywa kwale filimu yokwenziwa kwezinto.
i-pitting I-Pitting corrosion yenzeke xa ifilimu yokugqithisa kwicandelo lombhobho idilika, yenze imingxuma emincinci okanye imingxuma kumphezulu wombhobho.Imigodi enjalo inokuthi ikhule njengoko i-electrochemical reactions iqhubeka, ngenxa yoko isinyithi esinesinyithi sichithwa kwisisombululo esisezantsi emhadini.Intsimbi enyibilikisiweyo iya kuthi ke isasazeke iye phezulu emhadini ize ifake i-oxidize yenze i-iron oxide okanye irusi.Njengoko umngxuma uya usiba nzulu, ukusabela kwe-electrochemical ngokukhawuleza, i-corrosion iyanda, nto leyo inokukhokelela ekubhobhozeni udonga lombhobho kunye nokukhokelela ekuvuzeni.
Iityhubhu zichaphazeleka ngakumbi kwimingxuma ukuba indawo yazo yangaphandle ingcolisekile (Umfanekiso 1).Ngokomzekelo, ukungcola okuvela kwi-welding kunye nemisebenzi yokugaya kungonakalisa i-passivation oxide layer yombhobho, ngaloo ndlela yenze kwaye ikhawuleze i-pitting.Kukwanjalo nangokujongana nongcoliseko oluvela kwimibhobho.Ukongezelela, njengoko amathontsi etyuwa esiba ngumphunga, iikristale zetyuwa ezimanzi ezikwimibhobho zikhusela umaleko weoxide kwaye zinokukhokelela emhadini.Ukuthintela ezi ntlobo zosulelo, gcina imibhobho yakho icocekile ngokuyigungxula rhoqo ngamanzi amatsha.
Umzobo 1. I-316 / 316L ipayipi yensimbi engenasici engcolileyo nge-asidi, i-saline, kunye nezinye iidiphozithi zithinteka kakhulu kwi-pitting.
umhlwa.Kwiimeko ezininzi, i-pitting inokubonwa lula ngumsebenzisi.Nangona kunjalo, ukubola kwemingxuma akulula ukuyibhaqa kwaye ibeka umngcipheko omkhulu kubasebenzi nakubasebenzi.Oku kudla ngokwenzeka kwimibhobho enezikhewu emxinwa phakathi kwezixhobo ezijikelezileyo, njengemibhobho ebambeke endaweni eneendawo ezibambayo okanye imibhobho epakishwe ngokuqinileyo ecaleni komnye.Xa i-brine ingena kwi-gap, ekuhambeni kwexesha, isisombululo se-acidified ferric chloride (FeCl3) esinekhemikhali senziwe kule ndawo, esibangela ukukhawuleza kwe-corrosion ye-gap (Fig. 2).Njengoko umhlwa ngokwendalo yawo unyusa umngcipheko wokuhlwa, umhlwa kwimingxuma unokwenzeka kumaqondo obushushu asezantsi kakhulu kunemingxuma.
Umzobo 2 - I-Crevice corrosion ingaphuhliswa phakathi kombhobho kunye nenkxaso yombhobho (phezulu) kwaye xa umbhobho ufakwe kufuphi nezinye iindawo (ezantsi) ngenxa yokubunjwa kwesisombululo se-acidified acidified ye-ferric chloride kwi-gap.
I-Crevice corrosion idla ngokufanisa i-pitting kuqala kwi-gap eyenziwe phakathi kwecandelo lombhobho kunye nekhola yokuxhasa umbhobho.Nangona kunjalo, ngenxa yokunyuka kwe-concentration ye-Fe ++ kwi-fluid ngaphakathi kwe-fracture, i-funnel yokuqala iba nkulu kwaye ibe nkulu de igubungele yonke i-fracture.Ekugqibeleni, ukubola kombhobho kunokukhokelela ekugqobhozeni kombhobho.
Iintanda ezixineneyo zibonisa owona mngcipheko mkhulu wokudleka.Ngoko ke, izithinteli zemibhobho ezijikeleza inxalenye enkulu yomjikelezo wombhobho zivame ukuba yingozi kakhulu kunezithinteli ezivulekileyo, ezinciphisa indawo yokudibanisa phakathi kombhobho kunye ne-clamp.Abachwephesha benkonzo banokunceda ukunciphisa amathuba okonakala komhlwa okanye ukusilela ngokuvula rhoqo izilungiso kunye nokuhlola imiphezulu yemibhobho ukuze idle umhlwa.
I-Pitting kunye ne-crevice corrosion inokuthintelwa ngokukhetha i-alloy yensimbi efanelekileyo kwisicelo esithile.Abacacisi kufuneka basebenzise inkuthalo ekukhetheni eyona imathiriyeli yombhobho yokunciphisa umngcipheko wokubola, ngokuxhomekeke kwindawo yokusebenza, iimeko zenkqubo, kunye nezinye izinto eziguquguqukayo.
Ukunceda abacacisi baphucule ukhetho lwabo lwemathiriyeli, banokuthelekisa amaxabiso e-PREN esinyithi ukumisela ukuchasana kwabo kwi-corrosion yendawo.I-PREN ingabalwa kwi-chemistry ye-alloy, kuquka i-chromium (Cr), i-molybdenum (Mo), kunye nomxholo we-nitrogen (N), ngolu hlobo lulandelayo:
I-PREN iyanda kunye nomxholo we-corrosion-resistant elements of chromium, molybdenum kunye ne-nitrogen kwi-alloy.Umlinganiselo we-PREN usekelwe kwiqondo lokushisa elibalulekileyo (CPT) - elona qondo lokushisa liphantsi apho i-pitting yenzeke - kwiintsimbi ezahlukeneyo ezingenasici kuxhomekeke kwimichiza.Ngokusisiseko, i-PREN ilingana ne-CPT.Ke ngoko, amaxabiso aphezulu e-PREN abonisa ukuchasana kokugoba okuphezulu.Ukunyuka okuncinci kwi-PREN kufana nokunyuka okuncinci kuphela kwi-CPT xa kuthelekiswa ne-alloy, ngelixa ukunyuka okukhulu kwe-PREN kubonisa ukuphuculwa okukhulu kwentsebenzo kwi-CPT ephezulu kakhulu.
Itheyibhile yoku-1 ithelekisa amaxabiso e-PREN kwii-alloys ezahlukeneyo ezisetyenziswa rhoqo kwishishini leoli kunye negesi engaselunxwemeni.Ibonisa indlela ukucaciswa kunokuphucula kakhulu ukuxhathisa ukubola ngokukhetha umgangatho ophezulu we-alloy wepayipi.I-PREN inyuka kancinci ukusuka kwi-316 SS ukuya kwi-317 SS.I-Super Austenitic 6 Mo SS okanye i-Super Duplex 2507 SS ilungele iinzuzo ezibalulekileyo zokusebenza.
I-nickel ephezulu (i-Ni) igxininise kwinsimbi engenasici iphinda ikhulise ukuxhathisa ukubola.Nangona kunjalo, umxholo we-nickel wensimbi engenasici ayinxalenye ye-PREN equation.Kwimeko nayiphi na into, kudla ngokuba luncedo ukukhetha iintsimbi ezingenasici kunye nomxholo ophezulu we-nickel, njengoko le nto inceda ukubuyisela i-surfaces ebonisa iimpawu ze-corrosion yendawo.I-Nickel iyazinzisa i-austenite kwaye inqanda ukwakheka kwe-martensite xa igoba okanye ibanda i-1/8 yombhobho oqinileyo.I-Martensite sisigaba sekristale esinganqwenelekiyo kwiintsimbi ezinciphisa ukuxhathisa kwentsimbi engatyiwayo kwi-corrosion yendawo kunye nokuqhekeka kwe-chloride-induced stress.Umxholo we-nickel ophezulu ubuncinane we-12% kwi-316 / 316L yensimbi nayo iyanqweneleka kwizicelo zegesi ye-hydrogen yoxinzelelo oluphezulu.Ubuncinci be-nickel concentration efunekayo kwi-ASTM 316 / 316L insimbi engenasici yi-10%.
Ukonakala kwendawo kuyenzeka naphi na kumbhobho osetyenziswa kwindawo yaselwandle.Nangona kunjalo, ukucwiliswa kwemigodi kunokwenzeka ukuba kwenzeke kwiindawo esele zingcolisekile, ngelixa i-corrosion ye-crevice inokwenzeka kakhulu kwiindawo ezinezithuba ezimxinwa phakathi kombhobho kunye nezixhobo zokufakela.Ukusebenzisa i-PREN njengesiseko, inkcazo inokukhetha ibakala lombhobho ongcono kakhulu ukunciphisa umngcipheko walo naluphi na uhlobo lwe-corrosion yendawo.
Nangona kunjalo, khumbula ukuba kukho ezinye iinguqu ezinokuchaphazela umngcipheko wokubola.Umzekelo, ubushushu buchaphazela ukuxhathisa kwentsimbi engenastainless kwi pitting.Kwimozulu eshushu yaselwandle, i-super austenitic 6 molybdenum steel okanye i-super duplex 2507 imibhobho yensimbi engenasici kufuneka iqwalaselwe nzulu kuba ezi zixhobo zinokuchasana okugqwesileyo kwi-corrosion yendawo kunye nokuqhekeka kwekloridi.Kwiindawo ezipholileyo, umbhobho we-316/316L unokwanela, ngakumbi ukuba kukho imbali yokusetyenziswa ngempumelelo.
Abanini bamaqonga angaphandle konxweme kunye nabaqhubi banokuthatha amanyathelo okunciphisa umngcipheko wokubola emva kokufaka iityhubhu.Kufuneka bagcine imibhobho icocekile kwaye igungxulwe rhoqo ngamanzi amatsha ukunciphisa umngcipheko wokugqobhoza.Kufuneka kwakhona babe namagcisa olondolozo avula iziqhoboshi ngexesha lohlolo lwesiqhelo ukukhangela umhlwa kwimingxuma.
Ngokulandela la manyathelo angentla, abanikazi beqonga kunye nabaqhubi banokunciphisa umngcipheko wokubola kombhobho kunye nokuvuza okuhambelanayo kwimekobume yaselwandle, ukuphucula ukhuseleko kunye nokusebenza kakuhle, kunye nokunciphisa ithuba lokulahleka kwemveliso okanye ukukhutshwa kokukhutshwa.
Brad Bollinger is the Oil and Gas Marketing Manager for Swagelok. He can be contacted at bradley.bollinger@swagelok.com.
Ijenali yeTekhnoloji yePetroleum, ijenali ye-Flegship yoMbutho weeNjineli zePetroleum, ibonelela ngamagqabantshintshi agunyazisiweyo kunye namanqaku malunga nenkqubela phambili yetekhnoloji ephezulu, imiba ye-oyile negesi yeshishini, kunye neendaba malunga ne-SPE kunye namalungu ayo.