Electrochemical study of the corrosion rate of carbon steel in soil: Evolution with time and determination of residual corrosion rates under cathodic protection

► The corrosion rates of steel in two soils with different resistivity are compared. ► The influence of soil resistivity is negligible. ► The behaviour of steel in soil under cathodic protection is studied. ► Residual corrosion rates under cathodic protection are estimated via voltammetry. ► The methodology presented here could be used to monitor cathodic protection. Steel coupons were buried in soil boxes for 2.5months, with or without cathodic protection. A soil from the field was used and moistened by demineralized water or 5gL−1 Na2SO4 solution. Instantaneous corrosion rates were deduced from voltammetry experiments while average values were obtained by weight loss measurements. A detailed analysis of the polarization curves led to an estimation of residual corrosion rates (τrc) of coupons under cathodic protection. This residual phenomenon could be followed with time and it was observed that τrc decreased down to ∼10μmyr−1. Cathodic protection could be optimised with this methodology.