Abstract The potentiodynamic polarization and electrochemical impendence spectroscopy (EIS) techniques were employed to analyze the effect of salinity on electrochemical characteristics of J55 steel in high salinity CO2 brines. The results show that the CO2 corrosion mechanism of J55 steel is cathode control, corrosion rates increase as brine salinity increases from 12485ppm to 62423ppm, then decreases as the brine salinity increases from 62423ppm to 407997ppm. With increase of brine salinity, the corrosion potential shifts positively and the corrosion mechanism changes from electrochemical steps control to mixed mass transfer – electrochemical steps control. The higher the salinity is, the more obvious the mass transfer control is. The EIS plots present three time constants: capacitance loop in high frequency, inductance and capacitance loops in low frequency. The charge transfer resistance (Rt) decreases with brine salinity up to 62423ppm, then increases above 62423ppm. There are a minimum of Rt and a maximum of corrosion rates at about 62423ppm.
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