A study on hydrogen embrittlement of a high-strength pipeline steel weldment after microstructure manipulation by targeted heat treatments

Hydrogen embrittlement (HE) is a major concern when steel pipelines are used for hydrogen transportation and storage. The weldments of steel pipelines are of particular concern because they are reported to have higher HE susceptibility compare to the base metal. In this work, targeted heat treatments were used to manipulate the microstructure in a pipeline steel weldment to examine the effects of different microstructural features on HE susceptibility. Complementary analyses of the microstructure, mechanical testing, and fracture surface identified inclusions and ferrite morphology as the most dominant microstructural features that affect the susceptibility to HE. Specimens with different microstructures but sharing similar Ti-rich inclusions exhibited significant reductions in elongation to failure after hydrogen charging and showed brittle fracture surfaces decorated with multiple 'fish-eye' features. In addition, co-existence of bainitic microstructure with Ti-rich inclusions resulted in the highest susceptibility to HE.