The influence of stratum water composition on steel corrosion and the protective effect of the inhibitor in the presence of H2S and CO2

Corrosion of St3 steel and protective effectiveness of an inhibitory composition (25-200 mg/l), which is a solution of nitrogen -containing compounds (polyamines) in a mixture of organic solvents, were studied in model stratum waters MW1 and MW2, differing in the degree of mineralization, saturated with H2S and CO2 and containing 0.25 mg/L CH3COOH. Gravimetric methods have shown that the corrosion rate of steel in less mineralized MW1 environments is higher than in MW2 environments under static conditions both at room temperature and 80degree celsius, and in stirred solutions in the presence of a hydrocarbon phase. The protective effectiveness of the inhibitory composition in the presence of H2S in solution is higher in MW1, and in the presence of H2S and CO2, in contrast, in MW2 at room temperature and 80degree celsius. The presence of H2S and CO2 in the solution contributes to a higher protective effectiveness of the inhibitory composition in both stratum waters (Z= 90%) than in the presence of H2S (Z= 60-70%), both at room temperature and 80degree celsius. Under dynamic conditions at 10% hydrocarbon phase content, its value exceeds 90%. The influence of acetic acid present in the solution is discussed. The impedance spectroscopy method made it possible to evaluate the adsorption of the components of the inhibitory composition. This made it possible to calculate the surface coverage with an inhibitor, to determine the type of adsorption isotherm, and to calculate the adsorption free energy.