Study of the protection of carbon steel with an inhibitory composition in hydrogen sulfide environments by electrochemical methods

The protective effectiveness of the inhibitory composition of substances (25-200 mg/L) in relation to the corrosion of carbon steel in model stratum waters of oil and gas fields (M1 and NACE) saturated with hydrogen sulfide (400 mg/L) has been studied. The protective composition is a product of the interaction of fatty tallow polyamines with ethylene oxides in an alcohol solvent. The studies were carried out by the potentiodynamic polarization and impedance spectroscopy methods. An electrochemical diffusion technique was used to evaluate the effect of an inhibitory composition on the penetration of hydrogen into a metal. According to the potentiodynamic polarization data, the inhibitory composition slows down mainly the cathodic process on the steel electrode, causing a decrease in the corrosion current with a protective effect that increases with its concentration and reaches 87 and 94% at 200 mg/L in M1 and NACE media, respectively. Electrochemical impedance spectroscopy has shown that there is an increase in the polarization resistance with an increase in the concentration of the inhibitory composition, which corresponds to a decrease in the corrosion current in both media under study. In this case, the capacitance of the electrical double layer also decreases, indicating the adsorption of the components of the inhibitory composition on the steel electrode. This made it possible to calculate a surface coverage with an inhibitor, to determine the type of adsorption isotherm, which turned out to be the Temkin isotherm, and to calculate the adsorption free energy. The inhibitory composition reduces the penetration of hydrogen into the metal, starting from a concentration of 100 mg/L.