The effect of temperature, chloride concentration, nature of anions and cations as well as corrosion inhibitors (quats) on the pit initiation during the first 2 h of CO2 corrosion of pure iron and low alloy steel was studied at 5 bar CO2 in a window autoclave with video microscopic control. Above 45 °C pit initiation time is below 20 rain. The major part of the investigations was performed at 85 °C. While anions are effective mainly duer to their adsorption properties, the major effect of cations is based on
their charge transport efficiencies in electroneutralizing cathodic sites. CO2 pitting corrosion is mainly caused by the presence of bicarbonate ions. Halide ions inhibit at low concentration. The efficiency increases with the ion mass and adsorption energy.
Keywords: carbon dioxide, pitting, anionic/cationic effects, inhibitors, quaternary ammonium compounds,
pure iron, low alloy steel