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S ulfide stress cracking (SSC) has been regarded as a source of major failures in the oil and gas indus- try,1-3 KI][QVO [QOVQÅKIV\ MKWVWUQK and human losses. Generally, SSC is KTI[[QÅML QV\o two types: Type I and Type II. Type I SSC is referred to as stress- oriented hydrogen-induced cracking (SOHIC) in which a hydrogen-induced blister crack forms parallel to the applied stress. Type II SSC is considered to be cracking from typical hydrogen embrit- tlement.4 SOHIC is a manifestation of ;;+ WN KIZJWV [\MMT[ LMÅVML I[ KZIKSQVO that consists of linked cracks of small cracks lying in the rolling or forging plane of the steel.5-6 Hydrogen-induced crack- ing (HIC), SSC, and SOHIC often occur because of the trapping of H atoms gener- ated during the corrosion of steel in hy- LZWOMV []TÅLM 02 S) solution.4,7 stresses and severe hydrogen charging conditions can accelerate the formation of cracks. Crolet8 Both high Stress-Oriented Hydrogen- Induced Cracking of L360QS Steel points out that the combina- tion of stress and hydrogen initiates the formation of local HIC and then the formation of SOHIC. Furthermore, many studies9-10 reveal that the initiation of small HIC cracks is a necessary step in the formation of SOHIC, though SOHIC can occur in HIC-resistant ma- terials.11 Once an initial HIC forms, the KZIKS _QTT JM []JRMK\ \W \PM [\ZM[[ ÅMTL caused by two primary sources—both the residual and/or applied stress and hydro- gen pressure within the crack. Both ana- lytical and experimental evidence show that internal pressure alone can cause the linking of cracks, leading to stepwise cracking (SWC).12-15 Because of the correlation between HIC and SOHIC, HIC-resistant steels for many years have been considered to be the solution for restraint of SOHIC. Studies by Cayard, et al.,11 NACE International, Vol. 51, No. 11 however, show that HIC-resistant steels are more suscep- tible to SOHIC than conventional steels. Stress-oriented hydrogen-induced cracking (SOHIC) behaviors of L360QS steel were investigated using standard SOHIC tests. Results indicated that L360QS steel was susceptible to SOHIC. Besides severe hydrogen charging conditions and high stresses, microstructural inhomogeneity plays an important role in the formation of SOHIC. November 2012 MATERIALS PERFORMANCE 71 SHUQI ZHENG, CHUNYU LI, CHANGFENG CHEN, AND MING YANG, China University of Petroleum, Beijing, P.R. China YAMENG QI, Beijing University of Aeronautics and Astronautics, Beijing, P.R. China