Evaluation of the efficacy of alkylimidazolines in reducing the corrosion aggressiveness of oil-containing waters

The subject of the study is the study of corrosion processes of non-alloy steel St 3 in water-oil mixtures to create effective compositions of corrosion inhibitors for oil and oil refining industries. Corrosion aggressiveness of commodity and formation waters, waters present in crude oil, due to their high mineralization, the presence of various sulfur compounds, as well as acidification due to the formation of carboxylic acids and other acidic compounds. High corrosion activity of water-oil mixtures causes rapid destruction of equipment and pipelines. This not only significantly affects the economic performance of production due to the cost of replacing metal structures, but also causes great environmental damage due to environmental pollution by both petroleum products and highly mineralized waters. Therefore, one of the most important tasks is the protection of metal structures from corrosion in mineralized waters and water-oil mixtures. Given the prospects for the use of corrosion inhibitors of non-alloy steel, the effectiveness of alkylimidazolines (C15-C20) in water-oil mixtures depending on the characteristics of aquatic environments and the parameters of corrosion processes was studied. Given that the real formation waters of Ukraine's oil fields differ significantly in chemical composition and are difficult to model in the laboratory, a 3 % solution of sodium chloride with acetic acid, sulfite and sodium metabisulfite was used. Aqueous solutions were mixed with oil in a ratio of 140:10–180:10. The concentration of sodium chloride solution (3 %) is due to the high corrosion activity of this solution to ferrous metals, including solutions with a high level of mineralization. The choice of alkylimidazolines is due to the fact that they are promising inhibitors in both aqueous media in the presence of oil and in oil in the presence of mineralized waters in a wide range of temperatures. There are almost no data in the literature on the effect of pH, petroleum products, sulfites on the corrosion activity of mineralized media against non-alloy steel. There are no data on the effect of these parameters on the effectiveness of imidazoline corrosion inhibitors of steel. The processes of corrosion of steel St3 in 3 % solution of sodium chloride and its mixtures with oil at temperatures from 20 to 85 oC at pH change from 2.65 to 6.25 at concentrations of imidazolines from 2 to 50 mg/dm3 were studied. The impact on the corrosion of sodium sulfite and bisulfite in the presence of alkylimidazolines was evaluated. The effectiveness of alkylimidazolines in the aqueous medium as bactericidal inhibitors under anaerobic conditions has been determined. It is shown that corrosion aggressiveness in water-oil mixtures increases with decreasing medium pH and increasing temperature. A significant reduction in the corrosion rate was achieved with the use of alkylimidazolines. In some cases, the values of the degree of protection of steel against corrosion at the level of 80-90% at doses of inhibitor up to 50 mg/dm3. The use of imidazolines in the composition with sodium sulfite helps to increase the effectiveness of steel protection against corrosion. Alkylimidazolines (C15-C20) provided a high level of protection of steel from biocorrosion under anaerobic conditions.