A new computational framework is presented to predict the structural integrity of welds in hydrogen transmission pipelines. The framework combines: (i) a thermo-mechanical weld process model, and (ii) a coupled deformation-diffusion-fracture phase field-based model that accounts for plasticity and hydrogen trapping, considering multiple trap types, with stationary and evolving trap densities. This enables capturing, for the first time, the interplay between residual stresses, trap creation, hydrogen transport, and fracture. The computational framework is particularised and applied to the study of weld integrity in X80 pipeline steel. The focus is on girth welds, as they are more complex due to their multi-pass nature. The weld process model enables identifying the dimensions and characteristics of the three weld regions: base metal, heat-affected zone, and weld metal, and these are treated distinctively. This is followed by virtual fracture experiments, which reveal a very good agreement with laboratory studies. Then, weld pipeline integrity is assessed, estimating critical failure pressures for a wide range of scenarios. Of particular interest is to assess the structural integrity implications of welding defects present in existing natural gas pipelines under consideration for hydrogen transport: pores, lack of penetration, imperfections, lack of fusion, root contraction, and undercutting. The results obtained in hydrogen-containing environments reveal an important role of the weld microstructure and the detrimental effect of weld defects that are likely to be present in existing natural gas pipelines, as they are considered safe in gas pipeline standards.

翻译：本文提出了一种新的计算框架，用于预测氢气输送管道焊缝的结构完整性。该框架结合了：(i) 热-力学焊接过程模型，以及(ii) 基于相场的耦合变形-扩散-断裂模型，该模型考虑了塑性和氢陷阱效应，包含多种陷阱类型，并计及静态和演化的陷阱密度。这使得首次能够捕捉残余应力、陷阱产生、氢传输和断裂之间的相互作用。该计算框架被具体化并应用于X80管线钢的焊缝完整性研究。研究重点为环焊缝，由于其多道焊特性，环焊缝更为复杂。焊接过程模型能够识别三个焊缝区域（母材、热影响区和焊缝金属）的尺寸和特征，并对它们进行区别处理。随后进行的虚拟断裂实验显示出与实验室研究结果的高度一致性。在此基础上，评估了焊接管道的完整性，估算了多种工况下的临界失效压力。特别值得关注的是，评估现有天然气管道（考虑用于输氢）中存在的焊接缺陷对结构完整性的影响：气孔、未焊透、缺陷、未熔合、根部收缩和咬边。在含氢环境中获得的结果揭示了焊缝微观结构的重要作用，以及现有天然气管道中可能存在的焊接缺陷（这些缺陷在天然气管道标准中被认为是安全的）所带来的有害影响。