X-ray Absorption Spectroscopy study on methanogens influenced corrosion of metallic components from the natural gas network

The presence of hydrogenotrophic microorganisms as methanogens in natural gas reservoirs storing electrochemically produced hydrogen can significantly affect both the fuel stability and the degradation rate of metallic pipelines, resulting in significant economic losses. In this context, corrosion of metallic materials can manifest as a parasitic reaction in which the metallic substrate acts as an electron donor in competition with H2. However, the relationship between this corrosion mechanism and the methanogenesis process remains poorly documented. The aim of this study is to understand the corrosion mechanism affecting metallic components used in the natural gas network for hydrogen storage purposes by assessing the mechanism of crystallization of the corrosion products. To achieve this objective, preliminary corrosion experiments have already been carried out on carbon and copper-based alloys commonly used in the distribution network (carbon steel, a stainless steel, copper and brass) to verify the effect of methanogens on their electrochemical behaviour. An abiotic condition was also set up to define the effect of the solution (dissolved gas, ions). Biotic and abiotic coupons were then analyzed using sub-m surface-sensitive X-ray absorption spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) to verify the oxidation states of the main alloying elements and the degree of crystallinity of the corrosive patina. Chemically different corrosion products and variations in the degree of crystallinity due to methanogens were detected depending on the material and the conditions, which helped indicating the type of corrosion mechanism (direct or indirect) they underwent. Important information was also obtained on the evolution of the oxidation states of metals related to different electrochemical pathways for the production/degradation of methane.