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.