Flow Characteristics and Corrosion Mechanisms of Carbon Dioxide in Different Phases at Pipeline Defects

Corrosion at pipeline defects poses a significant risk to Carbon Capture, Utilization, and Storage (CCUS) infrastructure. However, the effect of the CO2 phase state on this corrosion is poorly understood. This study utilizes a multiphysics numerical model to investigate flow-accelerated corrosion (FAC) at these defects. Gaseous, liquid, and supercritical CO2 were systematically tested under relevant operating conditions (1–10 m/s, 2–13.38 MPa, 283.15–404.21 K). The simulations reveal several key findings. First, localized vortices at defects increase the corrosion current density by up to 97.2%. Second, supercritical CO2 is identified as the most aggressive phase, yielding a corrosion rate 2.1 times higher than the gaseous phase. Finally, for supercritical CO2, it was found that while elevated temperature and pressure promote corrosion, a higher flow rate locally inhibits it. This inhibition is due to high shear stress on the defect surface. The stress prevents a porous, nonprotective corrosion layer from forming and instead promotes a denser, more protective passive film. These findings provide crucial insights for designing and safely operating CO2 transport pipelines.