Corrosion of carbon steel and the passivating properties of corrosion films formed under high-PT geothermal conditions

Journal Article · 27 April 2019 · Science of the Total Environment

DOI: https://doi.org/10.1016/j.scitotenv.2019.04.386 · OSTI ID:1528904

Mundhenk, Niklas  ^[1]; Knauss, Kevin G. ^[1]; Bandaru, Siva R. S. ^[2]; Wonneberger, Robert ^[3]; Devine, Thomas M. ^[2]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Univ. of California, Berkeley, CA (United States)
3. Friedrich Schiller Univ., Jena (Germany)

Corrosion is a major obstacle to a safe implementation of geotechnical applications. Here, using a novel approach that includes vertical scanning interferometry (VSI) and electrochemical impedance spectroscopy (EIS) we discuss time-dependent carbon steel corrosion and film formation at geothermally relevant temperatures (80-160 °C) in CO₂-saturated mildly acidic Na—Cl brine. Iron dissolution kinetics follows a logarithmic rate at 80 and 160 °C and a linear rate at 120 °C. At 80 °C, high initial corrosion rates (first 24 h) generate H₂ at a minimum rate of 12 μmol h^-1 cm^-2 and lead to the formation of a continuous ~100 μm thick porous corrosion film. It exhibits a duplex structure with a crystalline outer FeCO₃ layer and an inner layer composed of a skeletal network of Fe₃C impregnated with FeCO₃. Being an electrical conductor we hypothesize the Fe₃C to strongly enhance corrosion rates by providing additional cathodic sites. Pseudo-passivity due to an anodic film-forming reaction (presumably Fe-oxide) was observed at 120 and 160 °C, soon followed by the initiation of pitting at 120 °C. Steady-state corrosion rates at 160 °C are at least one order of magnitude lower than for 120 °C. Lastly, our experimental approach demonstrated potential for general applicability in studying corrosion-related phenomena.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1528904
• Journal Information: Science of the Total Environment, Vol. 677, Issue C; ISSN 0048-9697
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English