Analysis of Errors in Using the Two Electrode and Three Electrode Polarization Resistance Methods in Measuring Corrosion Rates

An analysis is made of errors arising in the calculation of corrosion rates by the three electrode polarization resistance method used commercially. It is demonstrated that taking the mean value of the rates measured at ± 10 mV polarizations significantly improves the accuracy. Based upon fundamental electrochemical principles, the commercial two electrode method is analyzed for errors in calculating the corrosion rate. When there is no difference in corrosion potential between the two electrodes, the error in calculating the corrosion rate is similar to the three electrode method. However, when a potential difference does exist between the two electrodes, the two electrode method predicts a “weighted” average corrosion rate within a few %.