Effect of H₂S on CO₂ Corrosion of Mild Steel in High-Temperature Supercritical CO₂ Conditions

The effect of H₂S on the aqueous corrosion behavior of mild steel was evaluated at high-pressure and high-temperature (HPHT) conditions at a partial pressure of CO₂ of 12 MPa and a temperature of 160°C. The corrosion rate of steel samples was determined by electrochemical and weight loss measurements. The surface and cross-sectional morphology and the composition of the corrosion product layers were analyzed by using surface analytical techniques (scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction). Results showed that the corrosion rate decreased with time and no significant difference was observed in the presence of 1,000 ppm and 2,000 ppm of H₂S at HPHT CO₂ conditions. Surface and cross-sectional analyses revealed that the corrosion process was governed by the formation of FeCO₃ regardless of the presence of H₂S. Furthermore, the corrosion behavior of mild steel in these conditions did not depend significantly on flow velocity.