Thermally Sprayed Corrosion Resistant Alloy Coatings on Carbon Steel for use in Supercritical CO₂ Environments

Abstract

This paper reports the use of a thermal spray corrosion resistant alloy (CRA) coatings to mitigate corrosion of carbon steel in an environment containing high pressure, supercritical CO₂, H₂S and an aqueous phase. CRA coatings were sprayed onto carbon steel substrates and tested in 3.5 wt.% NaCl solution in 9.5 MPa CO₂ and 0.5 MPa H₂S at 40⁰C for 30 days. Microstructural characterization revealed that the coatings protected the steel substrate from CO₂/H₂S corrosion. The bare steel formed a mackinawite (FeS1-x) scale, while no such scale was seen in the case of CRA-coated steel. It can be concluded that thermally sprayed CRA coatings can provide a cost-effective corrosion mitigation method for infrastructure likely to be in contact with wet supercritical CO₂ containing H₂S. The same coatings can be used as inner lining of pipes for transport of impure CO₂. However, care must be taken to ensure that the thermally sprayed layer does not have any through porosity; else, such coatings may accelerate corrosion of the underlying steel due to galvanic interactions.