Mohammad Ali Mohtadi Bonab

In this paper, hydrogen diffusion behavior in pipeline steel is thoroughly investigated. The effect of various microstructural factors affecting hydrogen diffusion are discussed using literature review. The results of this survey show that the hydrogen diffusion in pipeline steels depends strongly on the microstructure of steel, crystallographic texture, dislocation density, grain size, presence of different elements, precipitates and inclusions. Based on the results, the interfaces between the retained austenite and martensitic layer are considered as the possible hydrogen trap sites. Moreover, the apparent diffusivity decrease due to hydrogen trapping by dislocations is well documented without need for cyclic loading. The grain size and nature of grain boundaries plays an important role in the hydrogen diffusion and trapping. There is an optimum grain size in which the hydrogen diffusion reaches its maximum value. Various elements, inclusions and precipitates which are present in the microstructure of pipeline steel have a considerable role in hydrogen diffusion. Based on the hydrogen microprint technique results, the increase in the grain size decreases the hydrogen trapping by triple junctions and grain boundaries.