Effect of sodium chloride on the electrochemical corrosion of Inconel 625 at high temperature and pressure

The effect of sodium chloride (NaCl) on the electrochemical corrosion of the Inconel 625 at 300 ± 2 °C and 16 ± 1 MPa was investigated by polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). The experimental results showed that NaCl stimulated the Inconel 625 electrochemical corrosion and the oxide film on the surface of corroded Inconel 625 became less stable with increasing NaCl concentration. The oxide film was duplex with an inner Mg, Al-rich layer of MgO+Al2O3, with probably some Cr2O3, and an outer Ni-rich layer, principally Ni(OH)2/NiO. The inner layer was more protective than the outer layer due to the precipitation of magnesium and aluminum oxide in the presence of Cl−. In order to explain the corrosion behavior of the Inconel 625, an oxide film growth mechanism was discussed in this research.