Abstract
Hydrogen plays a pivotal role in the transition to a decarbonized economy. Repurposing existing pipeline infrastructure offers a cost- and resource-efficient strategy to accommodate this energy shift. However, the compatibility of the current infrastructure with hydrogen must be ensured. Therefore, this study investigates the sensitivity of X65 vintage pipeline steel to hydrogen-assisted degradation. The material’s resistance to hydrogen embrittlement is strongly influenced by the heterogeneous microstructure, varying residual stress states, and non-metallic inclusions. The aim of this work was to identify the effect of hydrogen on fatigue crack propagation. A dedicated in-situ experimental set-up was developed to capture the local impact of hydrogen on the evolution of crack propagation. High-resolution characterization techniques (including SEM, STEM, TKD, ECCI, etc.) were used to identify the critical components that contribute to hydrogen-assisted degradation.
The results revealed an important role for the microstructural features and for hydrogen on the mechanical performance. Regarding the microstructure, the pearlite and bainite phases tend to hinder the crack propagation. Furthermore, hydrogen does not only alter the crack propagation mechanism and crack morphology, but also significantly accelerates the crack growth rate. The high plasticity in air strongly decreases upon hydrogen charging, evolving from a branched crack in air to a straight crack path in hydrogen. Hydrogen also provokes a localized deformation, lowering the stresses required for crack propagation. Besides, the blunted crack tip in air becomes sharp in the presence of hydrogen, associated to the hydrogen interaction with dislocations.
The insights highlight the importance of microstructure engineering in enhancing the mechanical resistance of pipeline steels in the hydrogen industry.