Effect of extremely high CO2 pressure on the formation of the corrosion film on 13Cr stainless steel

Abstract

The corrosion behaviors of 13Cr martensitic steel under different CO₂ partial pressures (4–28 MPa) were investigated by weight loss tests and surface characterizations. The results show that the corrosion rate of 13Cr steel shows a sharp increase under higher CO₂ pressure (28 MPa), which reached approximately 20–180 times as large as those under lower CO₂ pressures (4–12 MPa). Under the lower CO₂ pressures, a single-layered Cr(OH)₃ passive film forms and completely covers the steel surface. However, when the CO₂ pressure reaches 28 MPa, a very different corrosion film which contains an inner Cr(OH)₃ passive layer and an outer FeCO₃ layer forms, and the inner passive layer shows local damage. This phenomenon can be explained by the lower pH (∼2.75) and the higher H₂CO₃ concentration in the solution under the higher CO₂ pressure.