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

The dissolution of deposited, protective iron carbonate fi lms 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 fi lm dissolution, as well as to provide baseline data for further study of the possible synergistic effect between chemical and mechanical fi lm removal. To address this goal, a series of iron carbonate fi lm dissolution experiments was conducted covering a wide range of pH values (pH 3 to pH 6.1) and Reynolds numbers (Re = 3.68 × 10 to 1.84 × 10) using a rotating cylinder confi guration. The polarization resistance technique was used for implicit quantifi cation of fi lm removal kinetics via corrosion rate monitoring, whereas scanning electron microscopy was utilized for the purpose of residual fi lm characterization. The results suggested that chemical fi lm dissolution was governed by mass transfer and showed the strong dependence of fi lm removal kinetics on the level of saturation in the solution (pH value) and fl uid velocity. In addition, the physical mechanism of chemical fi lm removal has been explained and discussed in light of the obtained results.