Protective Iron Carbonate Films—Part 2: Chemical Removal by Dissolution in Single-Phase Aqueous Flow

The dissolution of deposited, protective iron carbonate films in oil and gas transportation pipelines may drastically enhance corrosive processes on steel surfaces, and thus, seriously affect the longevity of the equipment in use. An investigation had been carried out to get a better understanding of the kinetics and underlying mechanism of film dissolution, as well as to provide baseline data for further study of the possible synergistic effect between chemical and mechanical film removal. To address this goal, a series of iron carbonate film dissolution experiments was conducted covering a wide range of pH values (pH 3 to pH 6.1) and Reynolds numbers (Re = 3.68 × 10³ to 1.84 × 10⁵) using a rotating cylinder configuration. The polarization resistance technique was used for implicit quantification of film removal kinetics via corrosion rate monitoring, whereas scanning electron microscopy was utilized for the purpose of residual film characterization. The results suggested that chemical film dissolution was governed by mass transfer and showed the strong dependence of film removal kinetics on the level of saturation in the solution (pH value) and fluid velocity. In addition, the physical mechanism of chemical film removal has been explained and discussed in light of the obtained results.