Abstract: A technique for electrochemical measurement of the corrosion current (corrosion rate) determines the electrochemical parameters that are necessary to calculate the corrosion rate as they are contained in the harmonic current response to a moderate amplitude sinusoidal voltage perturbation applied to the corroding metallic component. The harmonic current response is analyzed at frequencies .sub.1 f, .sub.2 f, .sub.3 f, .sub.4 f, .sub.5 f and the rectification current response of DC current to the presence of a 20-50 mV AC voltage perturbation at a frequency f. The free corrosion current density, the free corrosion potential and the Tafel coefficients are calculated. The Tafel coefficient or Tafel slope is a measure of the exponential dependence at the rate of corrosion in a material. From these data, the dissolution current is calculated, which in turn is integrated with respect to time to yield a cumulative mass loss.

Abstract: A method of monitoring the rate of corrosion of a cathodically protected system, comprising superimposing a sinusoidal voltage on a cathodic protection voltage imposed on a portion of the system, measuring an anodic dissolution current in response to the superimposed voltage, and calculating the corrosion rate from the anodic dissolution current at the cathodic protection voltage potential.