Determination of corrosion rate by means of electrochemical methods such as polarization resistance is limited to open-circuit conditions. In the case of cathodic protection, a protected object is polarized to protection potential by means of negative total current, the value of which is thus useless for quantifying corrosion rate. Long-time response physical methods, such as weight loss or electrical resistance technique are only applicable for corrosion rate determination under cathodic polarisation. A novel electrochemical method employing two working electrodes allows us to determine instantaneous corrosion rate at impressed potential even if the total current is negative. Anodic current density is extracted from two consecutively measured currents. The shape of the carbon steel corrosion rate curve at the impressed potential in the potassium carbonate solution was determined. At pH 11, carbon steel was spontaneously passive, however, at cathodic polarization to the Kuhn's protective potential, substantially elevated corrosion rate was indicated. The shape of the corrosion rate – impressed potential curve was confirmed by electrical resistance sensors exposed to aerated aqueous electrolyte under the same conditions.Keywords: Double-electrode; Cathodic protection; Corrosion rate; Carbon steel
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