Estimation of residual corrosion rates of steel under cathodic protection in soils via voltammetry

Steel coupons were buried in soil for 2 months under cathodic protection. Their residual corrosion rates were deduced from voltammetry and weight loss measurements. In aerated soils, the current density due to O2 reduction, jK,O2, was modelled with a mixed activation-diffusion controlled kinetic. The anodic part jA of the current density j, computed as jA = j − jK,O2, obeyed Tafel law. Its extrapolation to the protection potential gave a corrosion rate (∼7 μm yr−1) consistent with that obtained from weight loss measurements. With a deficient protection, corrosion rates remained at ∼80 μm yr−1, a value given by both methods.