Hydrogen pipelines and embrittlement in gaseous environments: An up-to-date review

Pipelines represent the most economical and efficient means for transporting hydrogen in large volumes across vast distances, contributing to accelerated realization of hydrogen economy. Nowadays, the development of hydrogen pipeline projects, including repurposing existing pipelines for hydrogen service, has become a global interest, especially in those major energy-producing and energy-consuming countries. However, steel pipelines are susceptible to hydrogen embrittlement (HE) in high-pressure hydrogen gas environments, potentially leading to pipeline failures. In this review, we establish a comprehensive knowledge base for comprehending, testing, and evaluating the gaseous HE in pipelines by a thorough examination of relevant research work. In addition to an overview of some major hydrogen pipeline projects in the world, the article consists of four integral parts essential to gaseous HE studies, namely, methods for exposure of steels to high-pressure hydrogen gas; measurements of the quantity of H atoms inside the steels; stress-strain behavior of pipeline steels under high-pressure hydrogen gas exposure; and fracture and fatigue testing of pre-cracked steels within gaseous environments. Further research into gaseous HE in pipelines focuses on developing standardized, quantitative, and consistent methods to assess and define the susceptibility of pipelines to gaseous HE.