Evaluation of corrosion resistance of low alloy steel in catholyte solution

In process fluids extracted from oil-bearing horizons, a significant amount of corrosion-hazardous components, such as salt ions, dissolved gases, mechanical impurities and microorganisms, often cause the destruction of oil and gas equipment. The greatest danger to low-alloy steel is acid gases - carbon dioxide and hydrogen sulfide. The simultaneous presence of carbon dioxide and hydrogen sulfide in the water-oil emulsion leads to the development of local corrosion processes due to the formation of soluble corrosion products - iron hydrogencarbonate. Therefore, one way to prevent the development of electrochemical corrosion is to neutralize the acidic components of the process medium. Alkaline solutions, including sodium hydroxide, are used as neutralizer of acid components of oil. As a result of the neutralization reaction, salts are formed. The presence of sodium salts in oil can cause disruption of the process of its further processing due to contamination of the obtained oil products and catalysts. Therefore, application of the method of non-reactive neutralization of acidic components of the process medium of oilfields is an urgent task. As neutralizer of acidic components of process medium of oilfields it is proposed to use catholyte - solution saturated with hydroxide ions. The research work considers the principles of forming protective corrosion-resistant films on the surface of low-alloyed steel in the presence of catholyte. Comparative evaluation of corrosion resistance of iron hydroxide films in the model of produced water obtained on low- alloy steel A 516-55 in.solutions of sodium hydroxide and catholyte is shown. The study made it possible to establish the influence of catholyte on the kinetics of corrosion processes, and also revealed the dependence of the corrosion rate of low- alloy steel on the concentration of added sodium hydroxide or catholyte reagents at various pH values. Microscopic studies have shown that in the presence of catholyte, a thinner (plastic) film is formed, which has high corrosion resistance and has a protective effect.