SUSCEPTIBILITY TO STRESS-ORIENTED HIC OF AN X65 UOE LINEPIPE EVALUATED BY FULL RING TEST AND SMALL SCALE TESTS

摘要

Linepipes have possibility to encounter three types of crack morphology: SSC, HIC/SWC, SOHIC (Stress Oriented HIC) in the sour environment. For modern linepipes, SOHIC is concerned under applied stress, particularly in softened heat-affected zone. In this study, an X65 UOE linepipe was evaluated as CAPCIS type full ring test was compared with tensile tests conforming to NACE standard TM0177-90 method A on the susceptibility to SOHIC in weld. A rectangular tensile specimen 6.4mm in thickness provided the same result as the round bar specimen specified in the NACE standard in terms of threshold stress. Ruptured specimens showed SOHIC preferably induced in the softened HAZ. In contrast, no defect indication was obtained after the completion of the full ring test performed at the applied stress of approximately 98%SMYS above the threshold stress. The rectangular tensile test in which a single wide side was exposed to the environment was also conducted. No internal SOHIC was observed at the applied stress of 100%SMYS. This study concludes that the NACE standard is severer than CAPCIS type full ring test which can be substituted with the one-side exposed rectangular specimen from the viewpoint of evaluating the susceptibility to SOHIC.