New hydrogen pipelines require large capital investments. The potential exists for the conversion of existing natural gas transmission networks to transport hydrogen (blends). Normally, low carbon steel piping grades are recommended for hydrogen gas service. Higher steel grades may be allowed now but under certain conditions and after evaluation. As the European standards have not been updated yet for hydrogen usage, the American ASME B31.12 standard can provide some preliminary guidance on the requirements for converting such pipelines to hydrogen service. Option A is described by ASME B31.12, uses different factors to determine a design pressure and reduces the operating pressure, up to 50% compared to natural gas. Option B is described in ASME B31.12, uses fracture mechanic and allows to achieve higher operation pressures. The existing requirements are quite conservative and sometimes too restrictive for conversion of existing natural transmission pipelines to hydrogen, especially for higher grade pipelines. It should therefore be noted that the ASME standard is going to be reviewed.
European natural gas network consists of different pipeline materials with the majority of higher grades. Many of these pipelines probably do not fully meet all ASME B31.12 requirements. The question is how could the existing natural gas network be converted to transport hydrogen without compromising on safety and integrity?
DNV performed numerous hydrogen readiness studies and has assessed different existing natural gas networks, including X70 Grade pipelines with a view to transport hydrogen (blends).
Based on the results of the studies, it can be concluded that the existing high-grade pipelines can be used for hydrogen service, given that some mitigation measures are taken and some material testing is performed.