The Corrosion Mechanism of P110 and Cr-Containing Steels in Simulated High-Temperature and High-Pressure O₂/CO₂ Environments

A model was established for offshore gas injection wells to calculate the temperature and pressure distribution of the wellbore under gas injection conditions. The corrosion rate of steel casing materials, namely P110, 3Cr, 9Cr, 13Cr, and 13CrS, was measured based on the corrosion weight loss method, under the coexistence of O₂/CO₂ (0.1% O₂ content) at 135 °C and 48 MPa, using a custom high-temperature and high-pressure reactor. The microstructures and compositions of the corrosion products were analyzed by scanning electron microscopy and energy-dispersive x-ray spectroscopy. Notably, 13CrS and 13Cr exhibited the lowest degree of corrosion, whereas the corrosion rates of 3Cr and 9Cr were similar and relatively more severe, but P110 exhibited uneven comprehensive corrosion and the highest corrosion sensitivity. The corrosion morphologies of 3Cr and P110 were similar, and the difference in corrosion rate was not significant, indicating that the addition of a trace amount of Cr cannot significantly improve the corrosion resistance of the steel when O₂ and CO₂ coexist at high temperatures. Under the coexistence of O₂/CO₂ at high temperatures and high salinity, even for 13CrS, anti-corrosion measures are necessary to extend service life. During gas injection operations, the O₂ content should be minimized to avoid accelerated corrosion.