Abstract: Utilizing the existing natural gas pipeline network for hydrogen-blended transportation is an effective approach to facilitate the large-scale adoption of hydrogen energy. However, hydrogen embrittlement in pipeline steel hinders the rapid development of hydrogen-blended pipelines. Urgent research on hydrogen-induced crack propagation behavior, incorporating both experiments and numerical simulations, is essential to ensure the safety of constructing and operating hydrogen-blended pipelines. Focusing on the heat-affected zone of X80 pipeline girth welds, crystal orientation and size parameters were determined through electron backscatter diffraction tests. A finite element model was developed using the crystal plasticity constitutive framework, with zero-thickness cohesive elements embedded between grains to simulate grain boundaries. This model was used to analyze the initiation and propagation of intergranular microcracks at the mesoscale for different hydrogen volume fractions. The results indicated that the cohesive element grain boundary model aligns with existing observational test outcomes. Microcracks are likely to initiate in stress concentration areas at the junction of multiple grains and propagate bidirectionally along grain boundaries toward high-stress areas. In a hydrogen environment, new cracks gradually form and expand during the initial crack propagation process, subsequently merging with the original cracks. This phenomenon results in a differing crack propagation path compared to that in a hydrogen-free environment. Additionally, hydrogen blending decreases crack initiation strain and heightens the risk of microstructural crack initiation and propagation.