EFFECTS OF FERRITE/PEARLITE STRUCTURE ON HYDROGEN DIFFUSION IN PIPELINE STEELS

Long-distance pipeline transportation is one of the important development directions in the hydrogen energy development. The hydrogen diffusion and accumulation in pipeline steel would lead to mechanical properties degradation, and cause brittle failure under external load. Therefore, the hydrogen diffusion and accumulation in pipeline steels are an important technical reference to evaluate the compatibility of traditional pipelines and provide qualifications of pipeline steels for upgrading. In this paper, three grades of pipeline steels (X52, X65 and X70) and twenty-two types of steels are studied. Image processing and continuum scale simulation were conducted based on the actual ferrite/pearlite structure. The hydrogen diffusion and accumulation after long-term service were predicted. Considering the different hydrogen diffusion rates in ferrite, pearlite and grain boundaries, and the blocking effect of grain boundaries, the effects of pearlite distribution, diffusion direction and individual phase percentage on hydrogen diffusion were compared and quantified. The current study provided a new understanding of materials selection for long-distance hydrogen pipelines.