Hydrogen serves as a fundamental energy carrier essential for achieving global carbon neutrality, with long-distance pipeline transportation recognized as the most efficient approach for large-scale hydrogen delivery. Nevertheless, hydrogen embrittlement (HE) in pipeline steels constitutes a significant safety challenge for this infrastructure. This review presents a comprehensive and systematic analysis of HE in hydrogen pipeline steels, emphasizing the microstructural fracture mechanisms under hydrogen exposure, the microstructural regulation of hydrogen diffusion and trapping, the interplay of multiple influencing factors, strategies for HE mitigation, and numerical prediction methodologies. Critical factors including microstructural features, hydrogen transport dynamics, and the coupling effects between stress and hydrogen are examined in detail. The review systematically summarizes advanced HE mitigation techniques and strategies, encompassing microstructural engineering, surface modification, alloy composition optimization, finite element modeling, and machine learning applications. Additionally, several principal challenges confronting the field are identified: the ambiguous mechanisms underlying multi-field coupling effects, the limited translation of laboratory-scale findings to practical engineering contexts, especially with regard to multi-scale mitigation of hydrogen-induced fracture, and the incomplete advancement of artificial intelligence-based pipeline integrity assessment tools. To address these issues, the review proposes key research directions and recommendations for future investigations into HE in hydrogen pipeline steels.

This investigation elucidates the elevated-temperature (650 °C) monotonic mechanical response and very-high-cycle fatigue (VHCF) characteristics of Inconel 718 superalloys additively manufactured via selective laser melting (SLM), with a comparative assessment between the as-built and post-process heat-treated states. The results indicate that mechanical performance improves after heat treatment, primarily due to the formation of γ′ and γ″ precipitates, which interact with dislocations to strengthen the alloy. Relative to the as-built specimens, the fatigue strength of the specimen after heat treatment has increased by more than twice. For the as-built specimen, fatigue cracks nucleate at the specimen surface. However, in the high stress range, crack initiation in the heat-treated specimens consistently occurs at the free surface, whereas under low stress conditions, the crack initiation site transitions to the subsurface region encompassing internal defects. Post heat treatment, the fatigue crack trajectory adopts a markedly ductile and tortuous morphology, engendered by the concerted influence of grain-boundary (Laves/δ) precipitates that enforce repeated crack deflection, matrix-strengthening phases that homogenize plastic strain and the attendant reduction in local strain accumulation under the effect of cyclic load.