Experimental validation of electrochemical tomography to locate and quantify localized corrosion

Abstract

We present a step in the development of a novel non-destructive technique, called electrochemical tomography (ECT), which is able to locate and quantify localized corrosion of steel in porous media. In this work we show the first experimental validation of ECT with a controlled laboratory setup. Localized corrosion in porous media, such as the corrosion of buried pipelines and reinforced concrete, remains one of the largest problems in civil engineering. It often leads to the premature deterioration of engineering structures. To detect corrosion at an early stage, non-destructive testing methods are essential. Electrochemical tomography was developed to measure the local corrosion rate reliably and accurately. ECT uses electrical potential measurements, taken at the surface of the porous medium, in combination with a numerical model, to obtain the size and location of the actively corroding steel (the anode), as well as the corresponding corrosion rate. The technique relies on the accuracy of the numerical model, which simulates the electrical potential field in the porous medium as a function of the anode size, location, the medium’s electrical resistivity and externally applied currents at the surface. We investigate the accuracy of this numerical model using a controlled experimental setup in the laboratory, with a well-defined macro-cell corrosion system and a constant electrolyte environment. We show that if the kinetics of the steel are understood, in terms of the exchange current densities and Tafel slopes of the main corrosion reactions, we are able to accurately model the electrical potential field in the medium. Furthermore, we show that the model accurately handles externally applied currents in the range applicable in ECT. This gives us confidence that assumptions made on the numerical model, related to the electrochemical reactions taking place, are justified, and it brings us closer to the application of ECT on engineering structures.