Effect of O2 on the long-term operation and corrosion of steel X65 in CO2-H2O environments for direct supercritical CO2 power cycle applications

Abstract The corrosion resistance of high-strength low-alloy carbon steel was investigated in simulated conditions that exist in direct supercritical CO 2 power cycle heat exchangers. The experiments were performed at 80 bar for 500 h at either 50 ° C with samples exposed to H 2 O-saturated CO 2 and CO 2 -saturated H 2 O or 250 ° C undersaturated CO 2 . Exposures were conducted with and without O 2 . Corrosion rates were determined via mass loss measurements. Corrosion products were analyzed via X-ray diffraction. Morphology of the corroded surfaces were determined with scanning electron microscopy. Localized corrosion, pitting rate was determined using a optical profilometry. The results indicate that oxygen has a large effect on the corrosion rate of carbon steel in these environments while the effect of temperature is less significant. Pitting, in the absence of oxygen, was minimal and primarily located on polishing scratches. At 50 ° C, higher general corrosion and pitting rates were detected in CO 2 -saturated H 2 O than in H 2 O-saturated CO 2 .