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Oil-soluble and water-dispersible corrosion inhibitors are used to mitigate corrosion in pipelines. The performance of corrosion inhibitors has been described mainly in terms of the adsorption of surfactants on metal surfaces. However, the partition of the surfactant from oil to water and its dispersion in water should also significantly affect the corrosion inhibition mechanism of pipelines operating in metal-oil-water systems. Based on this perspective, we investigate the influence of oil on the dispersion process of surfactants. To this end, we measured the inhibition performance, surface tension, and dispersion into the aqueous phase for a simple model inhibitor consisting of stearic acid (surfactant) and alkanes (oil). The results indicate that the mixing of oil with surfactant increases the amount of dispersion in water by decreasing the interfacial tension, thereby improving the corrosion inhibition performance. This strongly suggests that the dispersion of surfactant in the aqueous phase is essentially important in the corrosion inhibition process in metal-oil-water systems as a preliminary step to the formation of hydrophobic film on the metal surface.
Hirano et al. (Tue,) studied this question.