An Investigation into the Change Leakage when Switching from Natural Gas to Hydrogen in the UK Gas Distribution Network

The H21 National Innovation Competition project is examining the feasibility of repurposing the existing GB natural gas distribution network for transporting 100% hydrogen. It aims to undertake an experimental testing programme that will provide the necessary data to quantify the comparative risk between a 100% hydrogen network and the natural gas network. The first phase of the project focuses on leakage testing of a strategic set of assets that have been removed from service, which provide a representative sample of assets across the network. This paper presents the work undertaken for Phase 1A (background testing), where HSE and industry partners have tested a range of natural gas pipework assets of varying size, material, age and pressure-rating in a new bespoke open-air testing facility at the HSE Science and Research Centre, Buxton. The assets have been pressurised with hydrogen and then methane, and the leakage rate from the assets measured in both cases. The main finding of this work is that the assets tested which leak hydrogen also leak methane. None of the assets were found to leak hydrogen, but not methane. In addition, repair techniques that were effective at stopping methane leaks were also effective at stopping hydrogen leaks. The data from the experiments have been interpreted to obtain a range of leakage ratios between the two gases for releases under different conditions. This has been compared to the predicted ratio of hydrogen to methane volumetric leak rates for laminar (1.2:1) and turbulent (2.9:1) releases and good agreement was observed.