Sharing: Hydrogen embrittlement sensitivity of in-service X60 pipeline steel in a hydrogen-enriched environment

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Reaching carbon peak and carbon neutrality are major challenges facing China’s energy development. As a clean energy source with great potential, hydrogen will become an important option for achieving these \"dual carbon goals\". At present, China’s hydrogen industry has entered a phase of rapid development, with demand for hydrogen in urban areas continuing to rise. Meanwhile, technologies for the safe and economical large-scale transportation of hydrogen have become a key bottleneck restricting the industry’s growth. Among the various methods of hydrogen transportation, pipeline transport offers significant advantages for large-scale, long-distance delivery. According to the findings published by the International Hydrogen Energy Committee, the cost of building new hydrogen transport pipelines is approximately 2 to 3 times that of natural gas pipelines, whereas the cost of modifying existing pipelines for this purpose is only 10% to 30% of the cost of building new hydrogen transport pipelines. Currently, the total length of natural gas pipelines worldwide is approximately 1.35 million kilometers, of which China’s natural gas pipelines total around 124,000 kilometers. A national natural gas transmission network has been essentially established in China. Introducing hydrogen into existing natural gas pipelines for transportation can significantly reduce the costs associated with transporting hydrogen, while also increasing the utilization rate of these existing pipeline systems. When pipelines transport hydrogen or hydrogen-containing media, hydrogen enters the interior of the pipe material through adsorption and diffusion. Hydrogen atoms accumulate at grain boundaries, inclusions, and other defects, which increases the risk of hydrogen embrittlement in the pipeline ； ZHUO et al. found that even a small amount of hydrogen can significantly reduce the fatigue life of X80 pipeline steel, while Liu Fang et al. discovered that for X65 pipeline steel, at a total pressure of 9 MPa, its susceptibility to hydrogen embrittlement increases as the hydrogen content increases ； Li Tianlei et al. found that in a hydrogen-doped environment at 3% (by mass), the fracture toughness of X70 steel decreased, while the fatigue crack growth rate increased. However, existing research on the hydrogen embrittlement sensitivity of pipes in hydrogen-containing environments focuses primarily on standard pipeline steels provided by steel mills, and systematic studies on the applicability of hydrogen transport in operational pipelines are still lacking. Affected by factors such as the long-term operating environment, differences in manufacturing processes, and loads, the hydrogen embrittlement sensitivity of in-service pipelines under hydrogen transport conditions may differ significantly from that of newly built pipelines. To ensure the safety and reliability of hydrogen blending upgrades in existing natural gas pipelines, a systematic study of the hydrogen embrittlement mechanism in such pipelines under hydrogen-rich conditions is of great engineering significance for determining the critical operating parameter limits for hydrogen transportation in existing pipelines. The author systematically conducted slow strain rate tests (SSRT) on straight pipe sections, bent pipe sections, and their (ring) welds in a hydrogen-enriched environment. By comparing the mechanical properties of the base material and the welded joint in air and hydrogen-enriched environments, this study focused on investigating the influence of hydrogen enrichment on key mechanical parameters such as the tensile strength, reduction of area, and elongation after fracture of the pipe fittings, aiming to provide experimental data and engineering guidance for assessing the hydrogen compatibility and safe operation of existing natural gas pipelines.