1。Introduetion Large diameter,high pressure gas transmissionPIPelines have been used more and more widely allover the world.In China,such PIPelines are exPandingrapidl丫With the development of the Pipeline network,safety and maintenanee beeome an imPortant task.AI-though every PIPeline 15 required for eoating and eathodieProteetion nowadays,onee the Proteetions were disabledor destroyed,the results were unPredietable. X70 steel,as new tyPe steel ProPosed by API in 1973for the first time,now has a tendeney.to expand脚 atly inthe world.In thew七st一to-East Natural Gasl丫ansmissionProjeet of China,X70 steel was seleeted as speeial ma-terial.In the Past its mechanieal Performanee had beenstudied饰some resear比ers【‘一4>,however,little has beendone about X70 steel eorrosion Performanee,50 few datahas been aceumulated before.Only from 2001 to 2003,by means of burying X70 sliees in Ku‘erle and Ge,ermuin Xinjiang Provinee and Qinghai Provinee of China,itwas found that X70 steel has a high liability to Pittingeorrosion and general eorrosion. The硫ets of anions sueh as 50遗一,oH一,NoJ ionson Pitting eorrosion had been largely studied before,se卜eral differellt metals were taken as exPerimental materi-als.Sherbini,et al.diseovered that anions ililiibit theac-tive dissolution and pitting eorrosion of Zn and the extentof inhibitionthe illhibitor电p。151己‘ends uPon the tyPe and eoneelltrationof The research of Re众屺y indieated thatthe eorrosion rate alld the nittinZ eorrosion of Sn were in-八,。。。。月‘一奋‘。。JJ;“~~八tL。“J~:~~习引~‘L~.,~。~。_。L~_,Crea名ea DV tne aQdltlon ot nallae 10llstvJ .otner researCnerSk。,,。。1。。。k奋。:~‘J从一;1。-.~。。。枯习7~101飞ITL:1。T。。刀八.。一」naVea且50 ODt山neQ 51】Illlar reSUltSL’一‘,J。Wnlle Lee tOUnd50茸一ions ean first impede pitting eorrosion,then aceel-erate the dissolution of the bare metal surfaee by formingtunnels乱tlle Dottom ot Pr任e粗Sting PltSL“,. In thisP即er,the Potentiodynamie Polarization扫口d SEM observatlons、vere used to evaluate thet Prof.,Ph.D.,towhomeorresPondeneeshouldbeaddressed, E-mall:lixiaogang99@263.net.corrosion behavior of X70 steel.The effeets of CI一alld50改一eoncentration were diseussed.In addition,elee-trochemieal resistallee was obtained from eleetroehemieal加pedance speetroseo伴(EIS).2.ExPerimental The working eleetrode was made of X70 steel with thefollowing chemieal eomposition(wt pet)C 0.061,51 0.24,Mn 1.53,P 0.011,5 0.0009 and balanee Fe.The sheetwas eut into test Pieces 10 mm in length,10 mm in widthand 5 nun in thiekness.Before measurements,each sPee-而en wa名mechanieally Polished with emery Paper uP tograde 1000,degreased with acetone,and then rinsed withdistilled water.The exPosed eleetrode surfaee area was1 em2. The eleetrolytes were NaCI and NaZSO4 solutionsmade uP with analytical grade reagents and distilled wa-ter.All exPeriments were Performed at 25OC,PH vajueof 9.Potentials reeorded in this PaPer were referred tothe saturated ealomel eleetrode(SCE),and a Pt sheetwas used as a eoufiter eleetrode. The Potentiodynamie me韶urements were made us-ing an EG&G model PAR 273 Potentiostat whieh waseontrolled勿a Personal eomPuter.The morPhology ofX70 steel surfaee after treatmellt in valious solutionswas examined by LEO一1450seanningeleetronmieroseope(SEM). Eleetrochemieal而Pedanee measurements were Per-formed with a Schlumberger model 1250 frequeney re-sPonse analyzer and a EG&G model PAR 273A Potentio-stat eontrolled by a Personal eomPuter.A three-eleetrodeset一uP wa￡used with imPedanee sPeetra being reeordedat the eorrosion Potential Ecorr,in the frequeney rangefrom 105 Hz to 10一2 Hz for all measurements.Beforestarting the Potentiodynamie and imPedanee measur合mellts a steady state was obtained as indieated by the dePotential in the eell being eonstant.At the beginning ofeaeh exPeriment,the eleetrode was immersed in the testsolution for 2000 5 at the oPen eireuit Potential.Cl‘concentra灯onl(rno盯L)Fig·1(a)A如die Polarization eurves for X70 steel in NaCI solutions at different eoneentrations,(b)relationshiP between the ba;value and CI一eoneent
More abstracts about the Effects of Cl- and SO_4~(2-) Ions on Corrosion Behavior of X70 Steel