Stern-Geary linear polarization method

Corrosion rates underground have been measured using the Stern-Geary linear polarization method (Section 5.8) as well as weight loss [4]. The former method has been useful, for example, in assessing the corrosion rates of footings of galvanized-steel towers used to support power flues [5]. 

Recall that both Tafel slopes are positive in this form of the equation. The Stern-Geary equation is the basis for the linear polarization method in which the polarization resistance is determined typically by scanning the potential from a value slightly below the corrosion potential to one slightly above the corrosion potential. It is an extremely easy technique that has been put to considerable use in corrosion monitoring. The polarization resistance can be determined by a simple two-point measurement at values above... 

The polarization resistance method is based on the observation that the polarization curve close to the corrosion potential is linear (Fig. 8-8), the slope AE/AI (AE = step in potential, AI = resulting current) being defined as polarization resistance, Rp. The technique is called linear polarization measurement (LPR). The Rp value is related to the corrosion current by the formula (Stern-Geary, 1957) ... 

Jones (1971,1972), based on kinetic considerations, postulated the adoption of a criterion for a permissible corrosion rate on the basis of a polarization characteristic of a given corrosion system determined beforehand. In order to determine the corrosion rate at polarisation potential CP> knowledge of the course of the partial curve of the anodic reaction is necessary. The first steps in the analysis of partial currents of corrosion systems were made by Stern and Geary (1957), who described the method of determination of the Tafel coefficient of the anodic reaction on the basis of direct current measurement results of the cathodic polarization curve. Extrapolation of the linear section of this curve to a corrosion potential Ej-orr allows reproduction of a fragment of the anodic polarization partial curve at chosen potential values, as a difference between the polarization current and the partial cathodic current. 

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