Kinetics of Corrosion Layer Formation: Part 1—Iron Carbonate Layers in Carbon Dioxide Corrosion

Abstract

Kinetics of iron carbonate layer formation in carbon dioxide corrosion has been investigated using a direct method-the corrosion layer weight-change method. The experiments were conducted in a glass cell at the temperatures from 60°C to 90°C, within an iron carbonate supersaturation range from 10 to 350. It was found that the calculated results obtained by the previous kinetics expressions, which were based on the traditional dissolved ferrous ion concentration change method, are one to two orders of magnitude higher than the experimental reaction rates obtained in the present study. Based on the new data, a more appropriate equation is developed to describe iron carbonate layer growth on the steel surface. The experimental results further suggest that the main source of the ferrous ions, which are involved in the formation of the protective iron carbonate layer, is the iron dissolution process. It has been clearly demonstrated that the formation of iron carbonate is directly related to the conditions at the steel surface, which frequently can be very different from the one in the bulk fl uid. CORROSION SCIENCE SECTION CORROSION-Vol. 64, No. 4 335 FIGURE 17. Comparison of scaling tendency (ST) in pure CO 2 corrosion under the following conditions: initial Fe 2+ concentration = 50 ppm (which then drifted down); pH 6.6; T = 60°C, 70°C, 80°C, and 90°C; and stagnant solution.

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