Corrosion of Various X-Series Pipeline Steels in Water-Saturated Supercritical CO2

Abstract Carbon capture, utilization, and storage (CCUS) pipelines may transport water-saturated supercritical CO2 (s-CO2) that can experience flow and trace impurities. We measured weight-loss corrosion of four pipeline steels (X65-1, X65-2, X70, X80) at 50 °C and 10 MPa under three conditions: (1) static, no additional impurities; (2) flow (600 rpm), no additional impurities; and (3) static with 200 ppm SO2 and 1000 ppm O2. Under flow, corrosion rates for X70 and X80 increased to ~0.106 and 0.086 mm/yr (≈3–4× their static ~0.03 mm/yr), whereas X65-1/-2 were less flow-sensitive (≈0.066–0.094 mm/yr vs. 0.061–0.072 mm/yr static). With SO2 + O2, acceleration was pronounced: ~5× for the X65 steels (e.g., ~0.329–0.383 mm/yr) and ~15× for X70/X80 (up to ~0.451 mm/yr). Phase analysis showed, on the steel surface, Fe3O4 formed after static exposure, FeCO3 formed under flow, and FeCO3 formed with FeS/FeS2 in the impurity case. These results highlight grade-dependent sensitivity to hydrodynamics and impurities, underscoring the need for targeted mitigation for higher-strength grades in CCUS pipeline service.