Passivation of X65 (UNS K03014) carbon steel in NaHCO3 solution in a CO2 environment

•X65 steel was passivated in 0.5 M NaHCO3 solution in CO2 at 0.7 MPa and 50 °C.•OCP of X65 steel appreciably shifted toward the noble direction.•Disordered precipitation containing the elements Fe Na and O on the surface of the FeCO3 film was observed.•The precipitation of disordered substance elevated OCP.

In this study, the use of NaHCO3 as a pH stabilizer for the corrosion control of X65 (UNS K03014) carbon steel in different environments was experimentally investigated. The experiments were conducted at room temperature and at 50 °C in 0.5 M NaHCO3 solutions purged with CO2. Electrochemical tests were conducted in a high-pressure, high-temperature autoclave. The constituents of the corrosion products were investigated through scanning electron microscopy and X-ray diffraction. The results showed that X65 steel can be passivated in 0.5 M NaHCO3 solution in a CO2 environment. Immersion in 0.5 M NaHCO3 solution in a high-pressure, high-temperature autoclave resulted in the formation of a dense corrosion film on the surface of the X65 steel.

Graphical abstractThe changes in open-circuit-potential of X65 steel in 0.5 M NaHCO3 solution in CO2 at 50 °C and 0.7 MPa.Figure optionsDownload full-size imageDownload as PowerPoint slide