f Iron mains and fittings in hydrogen service

Distribution Network Operators have investigated the potential to utilise iron mains and fittings in hydrogen service.
Iron mains operate at low (<75 mbarg.) or medium (<2 barg.) pressure, iron fittings at up to intermediate pressure (<7 barg.) depending on design. No iron mains have been laid since the 1980s, although certain grades of iron are still used to construct fittings, which includes valves.
The work was conducted by DNV. It examined the impact that hydrogen might have on iron of different grades and also the risk of explosion posed by hydrogen if it escapes from a buried main. In carrying out the analysis no account was taken of additional mitigation measures associated with hydrogen conversion (e.g. in home detection) which would reduce risk to members of the public.
To enhance confidence, at the request of Operators, IGEM assembled a ‘Peer review panel’ of material science and risk modelling experts from a range of backgrounds. Their role was to express their professional opinion of the findings. The reports produced by DNV and the peer review panel are attached to this report in the appendix.
The conclusion is that iron fittings and most iron mains expected to be in operation after the current replacement programme is completed in December 2032, can operate in hydrogen service.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.