Repurposing Offshore Gas Pipeline for Hydrogen Transport – A Case Study of the North Sea

The global push to reduce carbon emissions and achieve net-zero by 2050 has accelerated the transition from fossil fuels to cleaner energy sources like hydrogen. With numerous hydrogen projects developing across Western Europe, critical infrastructure is needed to safely transport hydrogen fuel. The extensive network of offshore gas pipelines in the North Sea offers a cost-effective solution by repurposing them for hydrogen transport. However, this poses significant challenges as these pipelines were not originally designed for hydrogen. Using the Scottish Area Gas Evacuation (SAGE) pipeline (off the coast of Scotland) as a case study, this paper presents a flow assurance analysis for repurposing offshore gas pipelines for hydrogen transport, identifying risks to ensure safety and reliability. The Computational Fluid Dynamics (CFD) study simulated the transportation of varying hydrogen concentrations (0%, 15%, 25%, 50%, 75%, 100%) under steady-state conditions. It investigated effects on flow velocity, temperature, pressure variations, and fluid density to identify risks such as erosion corrosion, hydrate formation, and hydrogen embrittlement. The analysis showed that increasing hydrogen concentration led to higher fluid velocity, with 100% hydrogen having a velocity profile 8.5 times that of 0% hydrogen. Transporting hydrogen concentrations above 25% increased the risk of wall thinning due to erosion corrosion. A sub-cooling effect near the pipe wall raised concerns about hydrogen-induced hydrate formation. Additionally, higher hydrogen concentrations increased the risk of hydrogen embrittlement due to decreased fluid density and increased gas diffusivity. These results provide crucial insights into the challenges of transporting hydrogen in pipelines originally designed for natural gas, highlighting the need for careful consideration and mitigation strategies.