Corrosion enhanced by hydrogenotrophic methanogens differently enriched on steel alloys

The microbiological corrosion induced by methanogens is mainly studied on steel alloys, these being widely used in the Oil&Gas sector, where the most significant phenomena have been found. Most studies show that the effect of CO2-rich environments, pH and flow conditions could modify the interaction of methanogens with the substrate as for the use of hydrogenase and the catalyzation of protective corrosion products, such as Siderite or Vivianite. In this work, the enrichment of a different pool of hydrogenotrophic methanogens and bacteria on the surface of different steel alloys, a pure Fe (ARMCO©, 0.02 wt.% of C), a duplex stainless steel (2205, with 22 wt. % of Cr) and a carbon steel (S355, 0.14 wt.% of C) was documented, starting from the same microbial pool. The corrosion induced by methanogens enriched media, in comparison with sterilized media, were documented during replicated two-week tests. Electrochemical investigations were performed using a three-electrode cell consisting of a working electrode (test alloy), a reference electrode (saturated Ag/AgCl electrode) and a counter electrode (titanium mesh). Investigations included open circuit potential (OCP) monitoring and electrochemical impedance spectroscopy (EIS). Chemical characterizations of the corrosion products and post-experiment observations were performed by SEM and micro-Raman spectroscopy (μRS). Molecular analysis by next generation sequencing (NGS) of 16S RNA was performed by swabbing the surface of the material and identifying the microorganisms constituting the microbial communities for each case. Results evidenced a different enrichment of microorganisms and corrosion products depending on the material.