Influence of hydrogen-enhanced plasticity and decohesion mechanisms of hydrogen embrittlement on the fracture resistance of steel

Hydrogen gas is a renewable energy source for electrical and transportation fuel for vehicular applications. However, the storage and transportation of hydrogen gas are challenging because of its very nature and impact on pipelines and storage tank/facility materials. This paper investigates the influence of hydrogen on the candidate fracture toughness (KQ) of low carbon steel immersed in acidic hydrogen environments for one year which has limited previous research. Steel specimens were coated from all sides except one surface to accurately quantify the influence of hydrogen diffusing from the environments into the specimens. Specimens were tested for crack tip opening displacement (CTOD) fracture toughness at six- and twelve-month intervals of immersion in acidic environments. Before KQ testing at various intervals, the hydrogen contents of the specimens were determined by an electrochemical approach. Based on test results, models for the degradation of KQ of steel were developed in accordance with the proposed hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) model (HELP + HEDE model) of hydrogen embrittlement. Furthermore, fractography of the specimens was performed to observe the synergistic action of HELP and HEDE mechanisms (HE), and their subsequent effects on the microstructure and fracture resistance of steel. The significance of the research is highlighted by its practical application for assessing the durability of steel structures and infrastructure against hydrogen environmental assisted cracking (HEAC). Furthermore, this paper highlights the synergistic activity of HELP and HEDE mechanisms of HE in steel and the importance of developing structures for storing hydrogen on a large scale.