The nonlinear current-voltage response which is characteristic of a corroding metal/electrolyte interface prohibits the use of corrosion resistance measurements in conjunction with the Stern-Geary relationship, to provide an in situ determination of corrosion rates, at potentials removed from the free corrosion potential.

In this paper we describe the development of a technique for the electrochemical measurement of the anodic corrosion current (“corrosion rate”) under conditions of an applied cathodic protection potential. Our effort has been directed towards a simplified theoretical treatment of the harmonic current response at frequencies of 1f, 2f, 3f, 4f… to a 20 to 50-mV AC voltage perturbation at frequency f.

Experimental verification of the theoretical treatment was obtained by comparing the results of harmonic analysis with those obtained by mass loss determinations for copper : nickel alloy specimens of varying geometries, in oxygenated synthetic ocean water, at various levels of applied cathodic polarization.