Effect of Temperature and Pressure on the Corrosion Behavior of X65 Pipeline Steel Used for Transporting Dense Phase CO₂ Fluids

The corrosion behavior of X65 pipeline steel in a dense phase CO₂ corrosion environment with low water content and impurities such as O₂, H₂S, SO₂, and NO₂ was studied through corrosion simulation experiments, surface analysis techniques, and hydrochemical simulation calculations. The influence of temperature and pressure on the corrosion rate of X65 steel and reasons were compared and analyzed. The results show that the changes of temperature and pressure had a significant impact on the corrosion rate of X65 steel, but did not change the corrosion mechanism of X65 steel. A corrosion product film mainly composed of FeOOH and FeSO₄ formed on the surface of X65 steel. In a dense CO₂ environment with a constant pressure of 10 MPa, an increase in temperature could reduce the corrosion rate of X65 steel. In a dense CO₂ environment at a constant temperature of 50 ° C, the corrosion rate first decreased and then significantly increased with increasing pressure. Within the experimental temperature and pressure range, X65 steel had the lowest corrosion rate in a dense CO₂ environment at 10 MPa and 50 ℃. The reason for the difference in corrosion rate of X65 steel caused by temperature and pressure changes was closely related to the changes in the amount of liquid phase formation and the content of corrosive substances in the liquid phase.