DIFFERENCES BETWEEN APPARENT POLARIZATION RESISTANCE VALUES OBTAINED IN THE TIME AND FREQUENCY DOMAINS

Anomalously large differences between values of the polarization resis tance R(p) measured in the time and frequency domains pose a serious p roblem in determination of the corrosion rate from the Stern-Geary equ ation. A theoretical model is used to derive expressions for a quantit ative interpretation of the effect of a number of parameters on the ap parent R(p) values obtained by de and ac measurements. Problems associ ated with the determination of the true R(p) value are discussed, and some relevant questions concerning the minimum frequency needed for im pedance measurements are identified.