Accelerated Hydrogen Embrittlement Screening via Small Punch Test: Case Study on X70 Pipeline Steel

The realization of a hydrogen economy depends on the development of robust infrastructure capable of safely storing and transporting hydrogen over long distances. Although new materials are constantly explored, significant efforts are also being made to repurpose existing pipeline infrastructure for hydrogen service. However, hydrogen embrittlement (HE) of metallic materials poses a critical challenge to this transition. Therefore, there is a strong need for accelerated testing methodologies to efficiently screen materials for hydrogen applications. The in situ small punch test (SPT) is well-suited for this purpose, owing to its minimal sample size, low hydrogen volume requirements, and the ability to conduct multiple tests safely. In this study, the gaseous HE behavior of pipeline steel API-X70 was investigated using the in situ SPT. The effects of hydrogen precharging time, punch velocity (strain rate), and hydrogen gas pressure on the embrittlement response were systematically examined. The results demonstrate that strain rate has a more pronounced impact on embrittlement than precharging time. Fractographic analysis of hydrogen-exposed samples shows characteristic features of embrittlement, including radial and circumferential cracks. Interestingly, the precharged samples exhibited extensive circumferential cracking, whereas samples tested under slow strain rates showed highly localized deformation with fewer secondary circumferential cracks. The degree of fracture localization was also found to increase with higher hydrogen gas pressures. This work provides detailed insight into the mechanisms driving HE in pipeline steel X70 by considering the interplay between hydrogen concentration, diffusivity, and strain rate during deformation.