Fatigue Characterization of Ex-service Pipeline Metals in the Hydrogen Environment

Reducing greenhouse gas emissions, particularly carbon dioxide, has become a key objective in global environmental policies, especially within the European Union. Achieving this goal relies on adopting renewable energy sources and eco-friendly technologies, with one promising approach being the blending of hydrogen with natural gas. This emerging trend in the energy sector represents a significant step toward decarbonisation. Blending hydrogen into the existing natural gas pipeline network is seen as a way to enhance renewable energy output, reduce domestic carbon emissions, and address the global carbon footprint. Many developed economies, including the UK, have devised strategies to support this transition. For example, the UK’s HyDeploy project aims to blend 20% hydrogen by volume with natural gas. However, introducing hydrogen into natural gas networks can affect the behaviour of pipeline materials through a phenomenon known as hydrogen embrittlement. This a process whereby hydrogen atoms diffuse into metals and alter their mechanical properties, by weakening the metal and making it more susceptible to cracking under stress, even at relatively low loads. Therefore, it is crucial to assess the durability of materials in hydrogen-rich environments to safely execute this project.
This research assessed the impact of hydrogen exposure on the mechanical properties of ex-service pipeline materials in the UK’s natural gas network. The fatigue properties under controlled temperature and pressure conditions of these materials were investigated. The specimens were exposed to a hydrogen-rich environment using specialized equipment, where they were soaked or charged with hydrogen for varying durations of up to nine months, allowing hydrogen to diffuse into the material.