HIC performance of heavy wall large-diameter pipes for sour-service applications under Fit-For-Service conditions

Testing of heavy wall LSAW large-diameter pipes of grade X65 to X80 for resistance to HIC (Hydrogen Induced Cracking) has been performed at test conditions representing less severe duty compared to NACE TM0284-2003 standard test conditions. The fitness of the material for intended applications (Fitness-For-Service) should be assured for in-field environmental conditions when the extent of HIC cracking is below specified limits. Test gases consisting of defined amounts of H₂S in CO₂ or N₂ representing partial pressures from 0.003 to 1 bar H₂S have been used in NACE TM0284 solution A and EFC publication no. 16 solution in a pH range from 3 to 6 for HIC testing. Pre-mixed commercially available as well as mixed in-situ test gases were utilized for the tests. Both methods of test gas generation showed comparable results. Also the effects of pH (constant and drifting) and test duration (96 h vs. 720 h) were investigated. The test specimens were evaluated by ultrasonic technique and by metallographic investigation according to NACE TM0284. The test results have been compared to SSC severity regions according to NACE MR0175 / ISO 15156-2 to define severely sour, mildly sour and non-sour test regions for the investigated steels.