High-temperature Corrosion of Ni-based Alloys in CO2-rich Gases

Abstract Future technologies require structural materials resistant to environmental degradation in high temperature CO 2 -rich environments. Herein we exposed several commercially available Ni-based alloys (230, 263, 282, 617, 625, 740H) to atmospheric pressures gases intended to simulate the compositions expected in future direct-fired supercritical CO 2 power cycles. The alloys were exposed to 95% CO 2 + 4% H 2 O + 1% O 2 and the same gas containing 0.1% SO 2 at temperatures of 600, 650, 700, 750, and 800°C for 2500 h. With minor exceptions, chromia scales formed on all alloys at all temperatures in the SO 2 -free gas, yielding parabolic growth rates that followed a clear Arrhenius temperature-dependence. Behavior in the SO 2 -containing gas was more complex. Generally, the alloys performed well at temperatures of 650, 750, and 800°C. While some alloys further performed relatively well across the whole temperature range, several of the alloys experienced chromia failure and higher oxidation rates at temperatures of 600 and 700°C. Deviation from protective behavior was associated with internal sulfide formation and, additionally for the case of 600°C, external sulfate formation. The thermodynamic and kinetic factors influencing the accelerated corrosion in the presence of sulfur are discussed. The results suggest that caution is required when assessing compatibility of Ni-based alloys for CO 2 -based systems when sulfur-based impurities are expected.