Stress-induced corrosion behavior of martensitic P91 steel in high-temperature and high-pressure supercritical carbon dioxide for brayton cycle system

Abstract

The corrosion behavior of alloy materials employed in high-temperature components of supercritical carbon dioxide (S-CO₂) Brayton cycle power generation systems is a critical factor influencing both the efficiency and service life of the system. In this study, we investigated the corrosion behavior of martensitic P91 steel exposed to S-CO₂ at 550 °C and 20 MPa for up to 1000 h. The effect of stress loading (0/210/420 MPa) on the corrosion behavior was studied using a four-point bending stress loading device. The results revealed that the surface of the specimen exhibited extensive corrosion areas, indicating that the corrosion type of martensitic P91 was uniform corrosion rather than localized corrosion. In addition, the corrosion layer on the surface displayed a carbon deposition phenomenon, which differs from the metal corrosion typically observed in conventional steam cycles. The thickness of the corrosion product layer on the specimen surface under three conditions were 15.6 μm, 17.6 μm, and 27 μm, respectively. All corrosion layers exhibited a double-layer structure, with the outer layer primarily composed of Fe₃O₄ and the inner layer mainly consisting of FeCr₂O₄ and Fe₂SiO₄. This indicates that stress loading has minimal impact on the phase composition of the corrosion products, but it accelerates the corrosion rate of the steel, increasing the thickness of the oxide layer. Additionally, the oxide layer thickness increases with rising stress values, accompanied by localized spalling.