Abstract
In this series of papers, AC induced corrosion of steel pipe under cathodic protection was investigated. In this Part III, the most realistic model was devised, i.e., the cathodic current was composed of the reductions of dissolved oxygen partly controlled by diffusion and of the water following the Tafel law. The cathodic protection potential necessary to mitigate the corrosion for various AC amplitudes were evaluated. In this modeling approach, no change of soil properties due to AC corrosion is considered. Mean DC values of corrosion potential shift and the corrosion current density in presence of AC signal were calculated in reduced scale making possible field applications by introducing an appropriate set of corrosion kinetics parameter collected without AC signal. In a highly corrosive soil, the reduction of dissolved oxygen is slow compared with that of the water reduction, and then the corrosion behavior becomes similar to the case examined in Part II.
Highlights
In this series of papers,[1,2] AC enhanced corrosion of underground steel structures under the cathodic protection was investigated by modeling and digital simulations
We considered that the mean DC current density in presence of AC signal corresponds to the corrosion rate of steel specimen
At high frequency, 1 kHz, almost whole AC current is by-passed through the double layer capacitance, and no Faradaic rectification is expected. Their experimental results and simulation calculation confirm our hypotheses used. In this Part III, the results of digital simulations were presented when the electrolyte resistance RE is no longer negligible, which may happen definitively during the corrosion enhancement induced by stray AC signal on underground steel pipelines covered with a thick organic coating and under a cathodic protection
Summary
In this series of papers,[1,2] AC enhanced corrosion (or AC corrosion) of underground steel structures under the cathodic protection was investigated by modeling and digital simulations. More realistic cathodic process than other publications in the literature was dealt with.[3,4] The cathodic reaction may follow a Tafel law corresponding to the reduction of water or may be composed of two reactions, the reduction of dissolved oxygen with partially diffusion limited process together with the reduction of water.[1,5] The former model involves two tafelian reactions, one for anodic dissolution of steel and another one for the cathodic process, this corrosion mechanism was named the bi-tafelian.[1,2,3,4] The latter involves three reactions, this corrosion
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