The formation of iron oxides layers over the tubes of a heat exchanger is a phenomenon that can make heat transfer difficult. A chemical process has been proposed for removing these iron oxides layers formed on Inconel 600 tubes. Electrochemical impedance spectroscopy is used as a tool for studying the different experimental conditions of this process. In this paper, the influence of the concentration of O2 on bulk dissolution and the effect of a corrosion inhibitor have been studied. An equivalent circuit for modelling the impedance data obtained is proposed. The apparent diffusion coefficients of Fe2+ and the thicknesses of the diffusion layers can be obtained by mathematical processing of the parameters fitted to the equivalent circuit components. The results obtained by modelling of the impedance data have been compared with other results obtained by different methods of evaluation of the chemical dissolution of iron oxides.