11284

10375

كارشناسي ارشد

شناسايي و انتخاب مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مهندسي مواد

1394

هشت، 79ص.: مصور

علي اشرفي، عبدالمجيد اسلامي

مرتضي شمعانيان، عباس آقاخاني

1395/03/23

مهندسي مواد

ID10375

87 Stress corrosion cracking behavior of API X70 pipeline steel weldment on a simulated soil solution Reza Sadeghi Reza sadeghi@ma iut ac ir Department of Materials Engineering Isfahan University of Technology 84156 83111 Isfahan IranDegree M Sc Language FarsiSupervisors Dr Ali Ashrafi E mail ashrafi@cc iut ac irDr Abdolmajid Eslami E mail m eslami@cc iut ac irAbstractOne of the major problems facing today s oil and gas industry is stress corrosion cracking SCC in theexternal surfaces of oil and gas buried pipeline steels In the present study the stress corrosion behavior of x 70 pipeline steel after shielded metal arc welding has been investigated For this purpose the alloy waswelded by low medium and high rates of heat input Microstructures of specimens were studied using lightand electron microscopes Stress corrosion susceptibility was evaluated using slow strain rate tests in c2simulated soil solution in the free corrosion potential and under cathodic potentials of 850 and 1200 mvwith respect to Ag AgCl 3 M KCl saturated Scanning electron microscopy was used to examine thefracture surfaces Different areas of weld HAZ and WM were evaluated using linear polarization andpotentiodynamic polarization methods The results showed that by increasing the heat input tensile strengthand hardness was reduced larger HAZ area gained and the grain size was increased SSRT results showedthat increasing the welding heat input will reduce the susceptibility to SCC Steel samples fail at decreasingelongation with increasing cathodic potentials because the role of anodic dissolution decreases and hydrogenembrittlement mechanism will be dominant SEM images obtained from samples confirm the brittle fractureof specimens tested in high cp potentials It was also observed that the cracks might grow in intergranularmode Linear polarization test showed that the susceptibility to SCC resistance is inversely related topolarization resistance Potentiodynamic polarization test showed the lowest rate of anodic dissolution ofwelded samples with higher heat input In general results showed that the susceptibility to SCC increases byreducing heat input due to the decrease of sensitive areas Keywords Weldment Pipeline Heat input API X70 Stress corrosion cracking

علي اشرفي، عبدالمجيد اسلامي

مرتضي شمعانيان، عباس آقاخاني