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. 316L, Ti, alloy C- 276 and alloy 625 were sprayed onto carbon steel substrate using a JP-5000 HVOF system and tested in 3.5wt.% NaCl solution at 10 MPa in a mixture of 95% CO₂ and 5% H₂S at 40°C for 30 days. Microstructural characterization revealed that the coating protected the steel substrate from supercritical CO₂/H₂S corrosion. The bare steel formed a sulfide 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/H₂S. 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.