Evaluation of Corrosion Rates from Polarization Measurements

Polarization measurements within 5 to 20 mV of the corrosion potential offer a powerful method for determining corrosion rates. In this paper, known methods for evaluating the corrosion current from polarization data are critically examined. It is noted that calculated currents are generally in error when the anodic and cathodic Tafel slopes are precisely known, due to non-linearity of the polarization curve. A new result is derived, which allows the corrosion current to be calculated without error if the Tafel slopes are known. Diagrams are presented which show the sensitivity of calculated corrosion rates to errors in estimation of the Tafel constants.