Tribo-corrosion behavior of C-steel in water-based emulsion drilling fluids containing green corrosion inhibitors: experimental and computational studies

This article reports a study on the corrosive wear of carbon steel in water-based emulsion drilling fluids containing green corrosion inhibitors, PEG-6 isotridecyl phosphate and PEG-2 oleamide. The latter was used for comparison purposes, which was previously demonstrated to exhibit good performance. The effectiveness of the drilling fluids with the inhibitors, especially PEG-6 isotridecyl phosphate, in suppressing tribo-corrosion was largely improved, evidenced by much lowered corrosion rate, coefficient of friction (COF) and tribo-corrosion, compared to those without the green inhibitors. The benefits of the inhibitors were influenced by the sliding speed (2, 3.5, 5 and 10 mm/s). With increasing the sliding speed from 2 mm/s to 5 mm/s, the corrosion rate decreased, but further increasing the sliding speed to 10 mm/s did not continuously reduce the corrosion rate. However, COF value of carbon steel was continuously decreased as the sliding speed increased from 2 to 10 mm/s. It was shown that the corrosion inhibitors resulted in a more protective film on the worn surfaces, and the adsorption equilibrium constants increased with respect to the sliding speed from 182.6 M−1 to 849.6 M−1 for PEG-6 isotridecyl phosphate and 6.70 M−1 to 28.1 M−1 for PEG-2 oleamide. First-principles calculations and molecular dynamics simulations demonstrated that the better performance of the PEG-6 isotridecyl phosphate inhibitor was ascribed to its stronger polymer film and higher adherence to the iron surface.