Corrosion of carbon steel in natural waters. Effect of oxygen and bicarbonate/carbon dioxide

The corrosive behavior of waters with different O content of 0.5-8 mg/L was detd. on mild steel specimens in a closed hydraulic circuit by the linear polarization resistance and impedance detns. Water compns. were fixed to differentiate the effect on corrosion rate of both the CO2 and HCO3-contents. The corrosion rate as function of O2 content shows 3 different behaviors. The corrosion rate increases with O2 contents 0-3 mg/L and is nearly const. with O2 from 4 to 8 mg/L, while there is a narrow range where the corrosion rate abruptly decreases. The corrosion rate for any O2 content, was more effected by the [HCO3-] than by {CO2}. An interpretation of these effects is given