Variation of carbon steel corrosion rate with flow conditions in the presence of an inhibitive formulation

This work is an extension of studies into the mechanism of inhibition of a carbon steel by a non-toxic multicomponent inhibitor (fatty amines associated with phosphonocarboxylic acid salts) used for the treatment of water in cooling circuits. In a previous work [N. Ochoa, F. Moran, N. Pébère, B. Tribollet, Corros. Sci. 47 (2005) 593], it was shown that the properties of the protective layers formed on the metal surface were dependent on the electrode rotation rate. Moreover, two distinct surface areas were visualised on the metal surface and the ratio between the two zones was dependent on the flow conditions. The present study focuses on the measurement of the corrosion rate from impedance diagrams obtained at the corrosion potential for different electrode rotation rates. The measured polarisation resistances correspond to the anodic process. A non-monotonic variation of the corrosion current densities was observed and explained by the variation of the ratio between the two layers, which each have different intrinsic protective properties. From the polarisation curves plotted in the same conditions, the non-monotonic variation was not shown. Independently of the electrode rotation rate, the corrosion current densities remained low. This study brought an original approach to the influence of flow on the corrosion rate in the presence of inhibitors.