Corrosion Behaviors of Ferritic and Martensitic Stainless Steels in H2o Containing CO2 and O2 at Elevated Pressures

Microstructure and phase composition of the solid corrosion products formed on commercial ferritic and martensitic steels with various chromium compositions were studied at conditions designed to simulate the working environment of low temperature components in direct supercritical CO₂ power cycles. All alloys were characterized prior to the corrosion experiments using wavelength dispersive X-ray fluorescence for determining elemental compositions, and microscopic evaluation for determining grain structures. Immersion experiments were carried out in a CO₂-saturated H₂O environment with dissolved O₂ at 50°C for 96 hours, at 0.1 MPa and 8 MPa. The corrosion products were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Alloy corrosion rates were calculated from mass difference following removal of corrosion products. Complimentary electrochemical experiments were also conducted in the same environment at 0.1 MPa. Linear polarization resistance, cyclic polarization, and electrochemical impedance spectroscopy were used to further evaluate alloy corrosion resistance.