Assessing Hydrogen Compatibility of Cast Iron in Gas Grids: A Comprehensive Review

The decarbonisation of the energy sector is driving increasing interest in the use of hydrogen as an energy carrier, with existing natural gas networks representing a potential infrastructure for its distribution. Before hydrogen can be widely introduced into these systems, the compatibility of the materials currently employed in gas networks must be thoroughly evaluated. While the behavior of carbon steels in hydrogen environments has been extensively investigated, considerably less information is available for the non-ferrous metallic materials that are widely used in low-pressure gas distribution systems. Distribution networks, which typically operate at pressures below 16 bar, include a broader range of materials and components than high-pressure transmission pipelines and are generally subject to fewer standardization requirements. Within this context, the Horizon Europe CANDHy project (Grant Agreement No. 101111893) aims to assess the suitability of non-steel metallic materials currently used in European gas distribution infrastructures for future hydrogen service. A survey carried out during the project identified cast irons as the most widespread non-steel metallic materials in these networks. This paper reviews the current understanding of hydrogen interaction with cast irons, including hydrogen dissociation, adsorption, solubility and diffusion, together with the principal mechanisms responsible for hydrogen embrittlement. The available literature indicates that exposure to high-pressure gaseous hydrogen at ambient temperature generally has little influence on the mechanical performance of cast irons. In contrast, hydrogen uptake during electrochemical charging or exposure to high-temperature hydrogen environments may lead to embrittlement. Under cathodic polarization, the susceptibility of cast irons appears to depend strongly on microstructural features, particularly the morphology, size and distribution of graphite within the alloy.