Experimental study on stress corrosion cracking behavior of high-strength steel in acidic marine environment

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ABSTRACT This study investigates the stress corrosion cracking (SCC) behavior of Nb–Ti microalloyed API 5L X70 high- strength low-alloy (HSLA) steel—widely deployed in marine flexible risers and subsea pipelines—under a simulated acidic sour marine environment (pH 3, 3.5 wt.% NaCl, H₂S saturation). While prior research has examined hydrogen embrittlement (HE) or anodic dissolution (AD) individually in high-strength steels, this work uniquely integrates slow strain rate tensile (SSRT) testing with in-situ potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and high-resolution fractography to concurrently assess mechanical degradation, electrochemical behavior, and fracture morphology. The results demonstrate pronounced SCC susceptibility, with a substantial reduction in ductility and time to failure in the corrosive environment compared to air. Electrochemical data revealed high corrosion rates, active dissolution, and a low-frequency inductive loop characteristic of hydrogen-related interfacial processes. Fractography confirmed predominantly brittle fracture modes, including quasi-cleavage and transgranular cracking, which directly correlate with the electrochemical signatures. This concurrent analysis provides new mechanistic insight into the synergistic operation of HE—strongly promoted by low pH and H₂S—and AD in Nb–Ti microalloyed steels, offering critical guidance for material selection and SCC mitigation strategies in aggressive marine service.

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