Corrosion Behavior of API 5L X65 Carbon Steel Under Supercritical and Liquid Carbon Dioxide Phases in the Presence of Water and Sulfur Dioxide

Depending on the capture process, liquid or supercritical carbon dioxide (CO₂) can contain impurities like water (H₂O) and sulfur dioxide (SO₂), increasing the likelihood of corrosion of carbon steel pipelines even if there is no free water in the system. To understand the corrosion risk for such pipelines, the present study focused on the effects of CO₂ phase change, water, and SO₂. Different CO₂ phases (liquid and supercritical) and concentrations of SO₂ (<1%) were simulated in an autoclave-based study. The corrosion rate of steel samples was determined with weight-loss (WL) measurements. The surface morphology and the composition of the corrosion product layers were analyzed using surface analytical techniques (scanning electron microscopy [SEM], energy-dispersive spectroscopy [EDS], and infinite focus microscopy [IFM]). Results showed that the corrosion rate decreased with decreasing SO₂ content in the supercritical CO₂ phase containing 650 ppmv of water with no localized attack. In contrast, in high-pressure liquid CO₂, significant localized corrosion was observed.