The corrosion resistance of steels and nickel based alloys was investigated in supercritical CO2 (sCO2). Two types of experiments were conducted. The first set of experiments were conducted in a low temperature aqueous environment to simulate conditions that would exist in direct sCO2 power cycle low temperature heat exchangers. The alloy investigated was X65. Experiments were conducted at 80 bar for 500 h. Samples were exposed to H2O-saturated CO2 and CO2-saturated H2O at 50°C or undersatersaturated CO2 at 250°C. Exposures were conducted with and without O2.
The second set of experiments were conducted in sCO2 environments to simulate conditions that would exist in indirect sCO2 power cycle high temperature heat exchangers and piping. Findings were compared with five other institutions. The alloys investigated were Gr. 91, 316L, HR 120, IN625, and 740H. Experiments were conducted at 20 MPa at either 550 or 700°C in 500 h increments up to 1500 h.
Corrosion rates for aqueous corrosion were determined via mass loss measurements. Parabolic mass gain rates were determined for high temperature oxidation via mass gain measurements. Corrosion products were analyzed via X-ray diffraction. Oxide cross-sections and morphology of corroded surfaces were determined with scanning electron microscopy (SEM). Transmission electron microscopy was used for cases where the resolution of the SEM was not sufficient.
Findings for the low temperature aqueous experiments indicate that oxygen and water content both play larger factors than temperature in the corrosion resistance of materials. Findings for the high temperature oxidation experiments indicate that HR 120 is the most cost effective alloy, at both 550 and 700°C, for use when considering corrosion resistance of materials. The six institutions were in good agreement for across the varied alloys.