Understanding the Influence of SO2 and O2 on the Corrosion of Carbon Steel in Water-Saturated Supercritical CO2

In this work, the general and localized corrosion behavior of X65 carbon steel in water-saturated supercritical CO2 conditions containing O2 and SO2 at 35°C and 80 bar is evaluated. The results indicate that crystalline FeCO3 formed in the presence of water and CO2; however, the combined introduction of small concentrations of O2 and SO2 (as low as 20 ppm and 2 ppm, respectively) changed its crystal morphology. Increasing the concentration of SO2 to 50 ppm and 100 ppm, while maintaining O2 content at 20 ppm, results in the formation of FeSO3 · 3 H2O. General corrosion rates increased significantly from 0.1 mm/y to 0.7 mm/y as a result of the increase in SO2 content from 0 ppm to 100 ppm based on 48 h experiments, while localized corrosion rates rose from 0.9 mm/y to 1.7 mm/y. Additional tests involving solution replenishment over 48 h indicated that the higher corrosion rates observed in the presence of SO2 did not present the worst case scenario corrosion rates and highlight the importance of having a system where the process fluid is continuously replenished. The corrosion product morphology and chemistry were identified through a combination of scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), and surface profilometry measurements.