Corrosion Behavior of Austenitic Stainless Steel in Supercritical CO2 Containing O2 and H2O

The corrosion behavior of 347H stainless steel was investigated in supercritical CO2 (sCO2) containing H2O and O2 simulating heat exchanger conditions that would exist in direct sCO2 power cycles. Thermodynamic properties of oxygenated sCO2 aqueous systems related to the corrosion phenomena was determined using NIST developed software REFPROP. The exposure tests of the corrosion samples were performed at a pressure of 80 bar and two temperatures, 50 °C and 248 °C up to 1500 hours. The samples were exposed to oxygenated H2O-containing CO2, and oxygenated sCO2-containing H2O. The corrosion rate of the alloys was determined by mass change measurements. The surface microstructure and composition of the corrosion films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XRD results for the corrosion products on the sample surfaces formed in the oxygenated CO2-containg H2O and water-containing CO2 and O2 at 248°C revealed the presence of Fe2O3 and Fe3O4,-rich phase, respectively. The XPS results revealed that the samples had thicker films after exposure to 0.01 O2/ 0.04 H2O ratio in CO2 at 248°C than at 50°C. The outer film layer contained Fe and O and the inner layer Cr and O at 248°C. Mostly Cr and O were found at 50°C.