23Rp V

Potential, mV (vs SCE)

FIGURE 11.5 Schematic showing typical polarization resistance plot.

Potential, mV (vs SCE)

FIGURE 11.5 Schematic showing typical polarization resistance plot.

c where Rp = AE/Ai and Rp is inversely proportional to the corrosion rate. The standard method for determining Rp and hence the corrosion rate is given in ASTM G59 Practice for Conducting Potentiodynamic Polarisation Resistance Measurements [16].

The above procedure is commonly used in industry although care must be taken that large overpotentials are not applied that invalidate the linearity of Eq. 11.10. In addition complications can arise when the open-circuit (free) corrosion potential changes over the period of the measurement. Finally the above procedure assumes that the anodic and cathodic corrosion reactions are not influenced by limitations in diffusion of species [17] and that the solution resistance of the electrolyte is low. Additional consideration of the above can be found in reference [18].

The practical considerations of evaluating corrosion rate are further detailed in Section 11.6.

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