Feasibility of determining corrosion rates by means of stray current-induced polarisation

To measure metal corrosion it is necessary to make direct physical contact with the specimen or component acting as the working electrode. The most widely used method for determining the corrosion current is electrochemical, the so-called polarisation resistance method. The feasibility of a new method to polarise the metal without the need for direct physical contact was investigated in the present study. The required potential shift is obtained by induction of a current using an external electrical field. The model used for calculation of the corrosion rate assumes that the applied current runs in parallel through the electrolyte and the metal, and electrostatically polarises the metal. The overall electrical resistance of the system can then be expressed as 1/Re+M = 1/R-e + 1/R-M , where Re+M is the total resistance measured, R-e is electrolyte resistance and R-M is resistance due to the metal. This latter resistance to electrostatic polarisation is related to the faradaic reaction, which was verified by comparison with the gravimetric losses. This resistance has been called inductive polarisation resistance R-pi to distinguish it from the traditional polarisation resistance R-p.