Mitigating Corrosion of Carbon Steel in Supercritical CO2 Environments using HVOF Coatings

This paper reports the use of HVOF-sprayed corrosion resistant alloy (CRA) coatings to protect carbon steel in supercritical CO₂-containing environments such as oil and gas wells. 316L, Ti, alloy C-276 and alloy 625 were sprayed onto carbon steel substrate using a JP5000 and tested in 3.5wt.% NaCl solution in 100bar CO₂ at 40°C and 80°C for 30days. Microstructural characterisation revealed that the coating protected the steel substrate from supercritical CO₂ corrosion. The bare steel formed a siderite (FeCO₃) scale while no such scale was seen in the case of CRA-coated steel. It can be concluded that thermally sprayed CRA coatings provide a cost-effective corrosion mitigation method for infrastructure likely to be in contact with wet supercritical CO₂. However, care must be taken to ensure that the thermally sprayed layer does not have any through-thickness porosity; else, such coatings may accelerate corrosion of the underlying steel due to galvanic interactions.