It proved possible to obtain a reliable estimate of the residual corrosion rate from voltammetry experiments in various soils and in various conditions of aeration and applied potentials. Steel coupons were buried in soil for 2 months under cathodic protection. In each case, the proposed methodology gave an average residual corrosion rate consistent with weight loss measurements. This method is based on the modelling of the cathodic part jk of the polarisation curve. The anodic current density is then computed by subtracting the modelled jk component from the overall current density j, i.e. ja = j - jk. Two cases could be treated. In almost anoxic conditions, where H2O reduction predominated, and in strongly aerated conditions, whereO2 reduction was controlled by charge transfer, a cathodic Tafel line (E = ac-bc log |jK|) could be used. When O2 reduction predominated with its kinetic partially controlled by diffusion, the Koutecky-Levich equation had to be used. 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.
Estimation of residual corrosion rates of steel under cathodic protection in soils via voltammetry
Bestimmung der verbleibenden Korrosionsgeschwindigkeit von Stahl unter kathodischem Schutz im Erdboden mit der Voltammetrie
Corrosion Science ; 73 ; 222-229
2013
8 Seiten, 8 Bilder, 4 Tabellen, 31 Quellen
Aufsatz (Zeitschrift)
Afrikaans
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