The corrosion behavior of 347H stainless steel was investigated in supercritical CO₂ (sCO₂) containing H₂O and O₂ to simulate heat exchanger conditions that would exist in direct sCO₂ power cycles.  To understand the thermodynamic properties of oxygenated sCO₂ aqueous systems related to the corrosion phenomena, thermodynamic modeling was performed using REFPROP software.  Samples were exposed to oxygenated water-containing CO₂, and oxygenated CO₂-containing H₂O. The exposure tests were carried out at a pressure of 80 bar and two temperatures, 50 °C and 248 °C. The environmental conditions were simulated by filling each 1100 ml autoclave with 400 ml of deionized water, bringing each autoclave to its respective test temperature, and then pressurizing it with a CO₂:O₂mixture having a molar ratio of 95:1.

The corrosion rate of each sample was determined by mass loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed using surface analysis techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS) for oxygen and chromium, and X-ray photoelectron spectroscopy (XPS).  Weight gain results reveal that the samples exposed to higher temperatures experience a significant increase in oxide growth compared to the lower temperature counterparts.  XRD results confirmed this result in that corrosion products present on the samples exposed to sCO₂ containing H₂O and O₂ and H₂O containing sCO₂ and O₂ at 50 °C were too thin for conventional Bragg-Brentano XRD to detect anything aside from the base material.  However, the samples exposed to the environments at 248 °C had sufficiently thick corrosion layers for this method.  The XRD results for the corrosion products on the sample surfaces formed in the oxygenated CO₂-containing H₂O and water-containing CO₂ environments at 248 °C revealed the presence of primarily hematite (Fe₂O₃) and magnetite (Fe₃O₄), respectively. These results indicate that the corrosion degradation mechanism for 347H in oxygenated H₂O containing sCO₂ is different from the mechanism in oxygenated sCO₂ containing H₂O at 248 °C.