2026 Hu 3Cr Steel High Salinity Corrosion

To investigate the corrosion behavior and mechanisms of 3Cr steel under high-salinity, high-Ca2+, and O2–CO2 conditions, we simulated the service environment of a western China oilfield (total salinity 250,022 mg/L, Ca2+ > 15,400 mg/L). Immersion and electrochemical tests were conducted at 120 °C under 0.5 MPa CO2 with O2 partial pressures from 0 to 0.4 MPa. The results showed that the uniform corrosion rate increased sharply from 0.6492 mm/a in pure CO2 to 4.8551 mm/a at 0.4 MPa O2, with localized corrosion notably aggravated. It was found that the high Cl− concentration acted as a crystallization inhibitor, forcing the FeCO3 corrosion product into an amorphous state. In pure CO2, the corrosion film displayed a multilayered architecture: a surface crystalline CaCO3 layer with micropores exhibiting inward/outward growth, an intermediate amorphous FeCO3 layer, and an inner amorphous Cr-rich oxide layer. This structure was governed by the kinetic dominance of Ca2+, which preferentially precipitated as CaCO3, thereby suppressing FeCO3 growth through interfacial competition and localized acidification. With O2 introduction, the synergistic effect of O2, Ca2+, and Cl− triggered the formation of a loose, porous Fe2O3/CaCO3 composite.