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

Niklas Mundhenk; Kevin G Knauss; Siva R S Bandaru; Robert Wonneberger; Thomas M Devine

doi:10.1016/j.scitotenv.2019.04.386

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

Sci Total Environ. 2019 Aug 10:677:307-314. doi: 10.1016/j.scitotenv.2019.04.386. Epub 2019 Apr 27.

Authors

Niklas Mundhenk¹, Kevin G Knauss², Siva R S Bandaru³, Robert Wonneberger⁴, Thomas M Devine³

Affiliations

¹ Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States. Electronic address: nmundhenk@lbl.gov.
² Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
³ University of California, Berkeley, CA 94720, United States.
⁴ Otto Schott Institute of Materials Research at the Friedrich Schiller University of Jena, 07743 Jena, Germany.

PMID: 31059874
DOI: 10.1016/j.scitotenv.2019.04.386

Abstract

Corrosion is a major obstacle to a safe implementation of geotechnical applications. 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 NaCl 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. Our experimental approach demonstrated potential for general applicability in studying corrosion-related phenomena.