Evaluation of Corrosion Rates from Nonlinear Polarization Data

Evaluation of corrosion rates from polarization measurements in the vicinity of the corrosion potential (the linear polarization method) depends on a knowledge of the Tafel slopes for the anodic dissolution reaction and for the corresponding cathodic process. A method is presented for derivation of these parameters from the polarization data. One calculation, based on the extent to which the polarization curve is symmetrical about the corrosion potential, yields a reliable value for the difference between the inverses of the two Tafel slopes. A second calculation computes the separate values of the parameters from this difference and measurements of the degree of nonlinearity in either the anodic or cathodic direction. This approach is presented in the form of a simple algorithm which gives Tafel constants of sufficient accuracy to make possible reliable calculation of the corrosion current from the polarization data.