Abstract:

Against the backdrop of the strategic imperative for carbon peak and carbon neutrality, the global energy infrastructure is undergoing a comprehensive restructuring toward cleaner, low-carbon, efficient, and secure energy architectures. Hydrogen energy has emerged as a critical secondary energy vector, playing an increasingly vital role in facilitating the transition to sustainable energy systems. The integration of hydrogen into natural gas pipelines represents a technologically and economically viable pathway, allowing the repurposing of existing infrastructure for large-scale, cost-efficient hydrogen transportation. However, the permeation and interaction of hydrogen with pipeline steels can induce hydrogen embrittlement, a degradation mechanism that significantly compromises structural integrity and operational safety. A fundamental understanding of hydrogen embrittlement mechanisms, along with the development of effective mitigation strategies for pipeline materials in hydrogen-blended service environments, is therefore essential to ensure the reliability and safety of energy infrastructure throughout this transitional phase. This study systematically evaluates the hydrogen embrittlement behavior of X70 pipeline steel welds in hydrogen-blended natural gas systems by means of slow strain rate tensile tests and fatigue crack propagation experiments. The experimental matrix encompasses hydrogen blending ratios of 10%, 20%, and 100%, in conjunction with hydrogen charging durations of 12 hours, 24 hours, and 48 hours, to comprehensively assess their effects on mechanical properties, fracture mechanisms, and hydrogen embrittlement susceptibility in the weld region. Results reveal that under cyclic loading, the weld zone displays markedly higher susceptibility to hydrogen embrittlement relative to the base metal. A non-monotonic dependence of embrittlement sensitivity on hydrogen concentration is observed, with a critical threshold identified at 20% hydrogen blending ratio, where the hydrogen embrittlement coefficient attains a maximum value of 15.22%. The fracture morphology transitioned from typical ductile dimples to a quasi-cleavage mixed mode. This phenomenon is attributed to the irreversible segregation of hydrogen at defects such as grain boundaries. The segregated hydrogen reduces the local interatomic cohesion through the hydrogen-enhanced decohesion mechanism, thereby inducing brittle fracture and exacerbating the material’s embrittlement tendency. Furthermore, the study identified 24 hours as the most sensitive time node for the response of X70 pipeline to the hydrogen environment. This research reveals the performance degradation mechanism and micro-damage mechanism of X70 steel welds in hydrogen-blended environments, providing an important theoretical basis and experimental data support for the safe operation control, life assessment, and integrity management of hydrogen-blended natural gas pipelines.

Key words: X70 pipeline steel, hydrogen embrittlement, slow strain rate stretching, fatigue crack propagation, fracture morphology, hydrogen-doped natural gas

摘要：

在“碳达峰、碳中和”目标引导下，能源系统正向清洁低碳、高效安全方向快速演进。氢能作为关键二次能源，其高效利用成为实现可持续发展的重要路径。掺氢天然气技术可依托现有管网设施，实现低成本、规模化输氢，但氢与钢管的相互作用易引发氢脆风险，威胁管道安全。因此，研究掺氢环境下管道材料的氢脆机理与防护策略，对保障能源基础设施安全转型具有重要意义。本文针对掺氢天然气管道输送中X70管线钢焊缝存在的氢脆风险，通过开展慢应变速率拉伸试验与疲劳裂纹扩展试验，系统研究了不同掺氢比10%、20%和100%以及不同充氢时间12 h、24 h和48 h对焊缝区域力学性能、断裂机理及氢脆敏感性的影响规律。研究结果表明，在疲劳载荷作用下，焊缝区域的氢脆敏感性显著高于本体，且氢脆敏感性随掺氢比例增加呈现非单调变化特征，其中20%掺氢比为关键脆化阈值，此时氢脆系数达到15.22%，断口形貌由典型的韧性韧窝逐渐转变为准解理混合型断裂。该现象归因于氢在晶界等缺陷处发生不可逆的偏聚。偏聚的氢原子通过氢致弱键效应显著降低了局部晶格结合力，从而诱发脆性断裂，并加剧了材料的脆化倾向。此外，研究还发现24 h是X70管道对氢环境响应最为敏感的时间节点。本研究揭示了X70钢焊缝在掺氢环境下的性能退化机制与微观损伤机理，为掺氢天然气管道的安全运行控制、寿命评估及完整性管理提供了重要的理论依据与实验数据支撑。

关键词: X70管线钢, 氢脆, 慢应变速率拉伸, 疲劳裂纹扩展, 断口形貌, 掺氢天然气