Corrosion of Carbon and Stainless Steels in H2O-sCO2 Environments for Power Cycle Applications

The corrosion behaviors of carbon and stainless steels were investigated in supercritical CO₂ (sCO₂ ) containing H₂O and O₂ simulating conditions that exist in direct sCO₂ power cycle heat exchangers. Thermodynamic properties of CO₂-H₂O-O₂ systems related to the corrosion phenomena were determined using NIST software. The exposure tests of the corrosion samples were performed at a pressure of 80 bar and two temperatures, 50 and 250 °C up to 1500 hours. The samples were exposed to H₂O-containing CO₂ and sCO₂-containing H₂O both with and without O₂. The corrosion tendency of the alloys was compared using mass change measurements. The surface microstructure and composition of the corrosion films were investigated using X-ray diffraction and scanning electron microscopy. The overall results indicate that the corrosion mechanism for each material in H₂O containing sCO₂ is different from the mechanism in sCO₂ containing H₂O and that the mechanisms for corrosion are different with the introduction of O₂.