Ignition and Flow Stopping Considerations for the Transmission of Hydrogen in the Existing Natural Gas Network

This work formed part of the H21 programme, whose objective is to reach the point whereby it is feasible to convert the existing natural gas (NG) distribution network to 100% hydrogen (H2) and provide a contribution to decarbonising the UK’s heat and power sectors with the focus on decarbonised fuel at point of use. Hydrogen has an ATEX Gas Group of IIC compared to IIA for natural gas, which means further precautions are necessary to prevent the ignition of hydrogen during network operations. Both electrostatic and friction ignition risks were considered. Network operations considered include electrostatic precautions for polyethylene (PE) pipe, and cutting and drilling of metallic pipes. As a result of the updated basis of safety from ignition considerations, existing flow stopping methods were reviewed to see if they were compatible. Commonly used flow stopping methods were tested under laboratory conditions with hydrogen following the methodologies specified in the Gas Industry Standards (GIS). A new basis of safety for flow stopping has been proposed that looks at the flow past the secondary stop, as double isolations are recommended for use with hydrogen.