Protecting steels against corrosion and the formation of mineral salt deposits

Аннотация

The paper studies the physicochemical properties of import-substituted and export-oriented nitrogen, amine and phosphorus new composite inhibitors for corrosion protection of steels as well as scaling obtained from local raw materials and industrial wastes. Inhibiting properties of corrosion and mineral salt deposit accumulation in acid and hydrogen sulfide environments have been determined. It was found that the efficiency of the inhibition process with the use of composite inhibitors in acidic and hydrogen sulfide environments obeys the Langmuir law. The values of activation energy of the adsorption process in these media and thermodynamic values (∆H, ∆S, ∆G). Keywords: inhibition, thermodynamics, corrosion of steels, inhibitor, protective mechanism, activation energy, Gibbs energy, corrosion rate, hydrogen sulfide. Introduction. Globally, corrosion protection of steel is one of the most important scientific, technical and economic problems. Because in industrially developed countries losses from corrosion of metals makeup from 2 to 4% of gross national product [1-3]. In the Republic of Uzbekistan, industrial scale as a result of research works has achieved significant results in studying the effect of inhibitors on corrosion of metal equipment, creation and implementation of new import-substituting, export-oriented, competitive inhibitors meeting the requirements of international standards, providing high efficiency even at low concentrations, safe in the application of new universal corrosion inhibitors. In this relation, the most effective neutral and weakly alkaline media inhibitors are nitrogen, amine, and oxygen-containing organic compounds [4-6], as well as organophosphorus zinc acids which effectively prevent corrosion and mineral salt deposits on equipment surfaces. Materials and methods of research. The object of the study is multi-component composite inhibitors created on the basis of nitrogen, amine and phosphorus-containing substances and the subject of the study includes the study of general patterns of inhibitor application mechanisms for anticorrosion protection and against the mineral salt build-up of steel samples using modern methods of physical and chemical analysis. Materials for research were the samples in the form of metal plates made of steel St.3 and St.12. Influence of nitrogen and phosphate-containing inhibitors on steel St.3 and St.12 corrosion rate was investigated by the gravimetric method in the model environment and using 5-10-3 mol/l solution of H SO (background). In addition, 2 4 experiments were conducted in 1-3% aqueous solution of NaCI, NaOH and 1-3% aqueous solution of Na S in the presence of H S. The duration of the tests was 48 and 760 hours. The inhibitors are a 2 2 transparent liquid mass, well soluble in aqueous and acidic media. No independent phase formation was observed during storage. Results and their discussion. Experimental data on the dependence of the inhibition process on concentration and temperature on the degree of corrosion protection of steel samples of St.3 and 12 grades in the presence of inhibitors and without them showed that the applied composite inhibitors synthesized on the basis of nitrogen, amine and phosphorus-containing local raw materials and processing waste have the protection degree at 25°C 88.5-94.4%, and at 40÷50°C this index is in the range 89.0÷99.7%. If the process temperature goes up to 70°C, the degree of anti-corrosion protection begins to decrease slightly up to values of 99.3÷90.4%. Using the gravimetric method based on time, temperature, inhibitor concentration and other indices it has been determined that during the process in aqueous, acidic and neutral medium, at increasing inhibitor concentration from 0.1% to 1.0% the index of corrosion protection is equal to 96.2%÷99.8%. The corrosion protection rate of imported inhibitors of the Nalco brand in our Republic is 87.6% at the temperature of 80°С. It is known that inhibition of acid corrosion of metals by organic compounds is caused mainly by surface shielding and activation factor (an increase of activation energy of corrosion process in the presence of inhibitors in relation to background). To 210 calculate activation energy, we plotted lgK-1/T (Fig. 1). Studies on corrosion of St.3 and St.12 in acidic solutions in the presence of inhibitors containing amino- and phosphate groups showed their high efficiency. Fig.1. Dependence of lgK on the inverse temperature of the corrosion process ofs teels St.3 and St.12: 1 - Background; 2 - Sinh -1.0 mol/l; 3 - Sinh -1.25 mol/l; 4 - Sinh -2.5 mol/l; 5 - Sing -5.0 mol/l; 6 - Sinh -10.0 mol/l. The best inhibitor of corrosion of St.3 in the studied conditions recognized, in a series of alkylamines, phosphate-diethylmethacrylate, apparently because of the large number of radicals in its molecule and their size, so that the required protective concentration of this inhibiting system is minimal, in comparison with the other studied ami