Influence of sandblasting and hydrogen on tensile and fatigue properties of pipeline API 5L X52 steel

The evaluation of static properties and lifetime of a pipeline notched under the impact of sand with or without the presence of hydrogen has been performed. The material damage was made by electrolytic hydrogen and projecting corundum particles (aluminium oxide). It has been shown that sandblasting and hydrogen have little affect on the yield stress and ultimate strength. The material lifetime and elongation at fracture are clearly affected by hydrogen, which penetrates into the surface layers of the material and changes the local fracture mechanism. Despite the erosion of these layers, under the sand impacting, failure strain and lifetime are improved. The observation of failure mode shows that the deformation field, after sandblasting, is very important. The crack propagation and the failure seem to be intra granular. The cracks, in the pipeline API 5L X52 steel charged with hydrogen, propagate following the porosity path without any distinct direction. The absorbed hydrogen atoms placed inside the crystalline sites of steel cause the embrittlement of material so that a small effort is sufficient to create cleavage. Modified notch failure assessment diagram was used to evaluate the dangerousness of studied notch defect in different environments: air, hydrogen and sandblasting.