The article investigates hydrogen bulk diffusion and saturation in X70 pipeline steel, crucial for the European energy transition. With a focus on the power-to-gas concept, which aims to store renewable energy as hydrogen, the study emphasizes the importance of understanding hydrogen embrittlement in steel for pipeline safety. The research delves into the interaction between hydrogen atoms and crystal defects, illustrating how this interaction affects the diffusion and saturation of hydrogen in steel materials. By utilizing high-pressure gaseous hydrogen charging, thermal desorption analysis, and numerical modeling, the study provides insights into the diffusion behavior of hydrogen in X70 steel. The findings of the study suggest that a unified diffusion model can accurately simulate hydrogen diffusion, trapping, and saturation in pipeline steel, irrespective of the hydrogen source. The implications of the research extend to the repurposing of pipelines for hydrogen transport and assessing the risk of hydrogen embrittlement in pipeline materials. Overall, the article sheds light on the critical role of hydrogen diffusion modeling in ensuring the safety and efficiency of gas pipelines as part of the energy transition strategy in Europe.