Protective Iron Carbonate Films— Part 1: Mechanical Removal in Single-Phase Aqueous Flow

The protective role of iron carbonate fi lms deposited on steel surfaces as by-products of carbon dioxide (CO2) corrosion may be hindered by mechanical fi lm removal due to hydrodynamic forces. Damage to the fi lm is frequently accompanied by severe corrosive attack, which may ultimately result in costly equipment failure. The present work reports on experimental investigations of mechanical fi lm removal (its kinetics and level of damage to the fi lm) using a rotating cylinder confi guration in the highly turbulent fl ow regime. Corrosion rate monitoring using the linear polarization resistance technique was used as a tool for implicit fi lm removal rate measuring, whereas scanning electron microscopy served for verifi cation and evaluation purposes. Two types of fi lms were studied, one less uniform and adherent and the other more compact and adherent. The results clearly show that pure mechanical removal in undisturbed single-phase fl ow does occur. However, fi lm removal starts after an initiation period and is only localized. The differences in the thickness, microstructure, and topography of intact and residual fi lms are discussed in detail for both fi lm types. In addition, the possible mechanism of mechanical fi lm removal from the fl uid mechanics point of view has been proposed.