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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.
Sulfide stress cracking (SSC) has been regarded as a source of major failures in the oil and gas industry,1,3 causing significant economic and human losses. Generally, SSC is classified into two types: Type I and Type II. Type I SSC is referred to as stressoriented 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 embrittlement.4 SOHIC is a manifestation of SSC of carbon steels, defined as cracking that consists of linked cracks of small cracks lying in the rolling or forging plane of the steel.5,6 Hydrogen-induced cracking (HIC), SSC, and SOHIC often occur because of the trapping of ? atoms generated during the corrosion of steel in hydrogen sulfide (H2S) solution.4,7 Both high stresses and severe hydrogen charging conditions can accelerate the formation of cracks.
Crolet8 points out that the combination of stress and hydrogen initiates the formation of local HIC and then the formation of SOHIC. Furthermore, many studies""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 materials." Once an initial HIC forms, the crack will be subject to the stress field caused by two primary sources - both the residual and/or applied stress and hydrogen pressure within the crack. Both analytical 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.," however, show that HIC-resistant steels arc more susceptible to SOHIC than conventional steels. Several authors16"1" have investigated the effect of inclusion and microstructure on HIC, and showed that inclusions and pearlite colonies play die part of initiation sites for HIC. Meanwhile, the effect of microstructure on SOHIC was also investigated. Studies by Amano, et al.13 show that SOHIC resistance...