Abstract:
Objective The centralized supply of hydrogen resources and the rapid growth in market demand have made large-scale hydrogen transportation via long-distance pipelines a promising trend for future hydrogen energy supply, given its significant economic advantages. However, during pipeline operation, hydrogen atom permeation in pipeline steel may cause various forms of hydrogen-related damage, resulting in pipeline failure. Therefore, it is essential to evaluate the pipeline steel adaptability for extended hydrogen-contacting service.
Methods An X-ray diffractometer was used to analyze corrosion products on the inner surface of the pipeline in service, followed by nondestructive testing using ultrasonic waves and digital X-ray imaging. The hydrogen permeation behavior was investigated through in-situ gas phase permeation tests combined with electron backscatter diffraction analysis. Finally, slow strain rate tensile tests and fatigue crack propagation tests were conducted at varying hydrogen blending ratios to assess the impact of hydrogen on the tensile and fatigue properties of 20 steel in service.
Results Corrosion was observed on the inner surface of 20 steel in service, primarily consisting of iron oxide and ferroferric oxide. Due to minimal pressure fluctuations and the insignificant effect of alternating loads, no flaw waves were detected in the pipeline segment, and no internal surface or buried cracks were found. The grain size was small, with high-angle grain boundaries accounting for 91.7%. The uniformly distributed hydrogen traps effectively reduced the sensitivity to hydrogen embrittlement.
Conclusion The hydrogen-induced embrittlement coefficient of 20 steel at a 10% hydrogen blending ratio exceeds 25%, indicating significant degradation of plasticity and a higher likelihood of embrittlement under high-stress loading conditions. However, the fatigue crack propagation rate remains largely unaffected across different hydrogen blending ratios, indicating low sensitivity of hydrogen embrittlement to the change of hydrogen blending ratio. Consequently, the steel demonstrates a good fatigue property in hydrogen-contacting environments.
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