Fracture behaviour of pipeline steel depending on hydrogen content in material

The effect of hydrogen in pipeline steel on its fracture behaviour has been evaluated based on the failure tests of the notched and cracked beam specimens with different hydrogen content in the material. We propose a special index showing the loss of the resistance to fracture of the steel depending on the hydrogen content in the steel. Three characteristic ranges of the hydrogen content that correspond to different features of the hydrogen influence on the microstructural fracture specificity of pipeline steel have been found, namely: the zone of enhanced deformability of material, the transition zone with the mixed mechanism of hydrogen effect, and the zone of hydrogen embrittlement. It has been found that the ratio of diffusible/residual (trapped) hydrogen in the steel defines such microstructural fracture behaviour. The SEM examination of the fracture surfaces confirmed this relationship.