Development and performance evaluation of a synergistic composite inhibitor against electrochemical and microbiologically influenced corrosion

This study is devoted to evaluating the protective performance of a newly developed composite inhibitor system under complex corrosion conditions involving sulfate-reducing bacteria (SRB) and electrochemically active components. The main objective was to design synergistic composite inhibitors that provide high protection efficiency at low concentrations. Among the individual reagents tested, "Neftqaz-2013" exhibited 90% corrosion protection efficiency in an electrochemical environment at a concentration of 1.0 mg/L, but its activity was limited under microbiological conditions. Specifically, the growth rates of Desulfovibrio and Desulfomicrobium SRB strains reached 78% and 80%, respectively, while the concentration of biogenic hydrogen sulfide decreased only to 77 mg/L. Conversely, the "MARZA-1" reagent showed relatively weak bactericidal action against SRB; even at the highest dosage, the growth rates remained within 82–84%, and the H2S level decreased to 38 mg/L. To overcome these limitations, both reagents were combined in different ratios to obtain a series of complex NMK-type compositions. Among them, the NMK-3 composition (1:19 ratio) provided the best performance, ensuring 98% corrosion protection in an electrochemical medium and 99% and 97% inhibition of Desulfovibrio desulfuricans and Desulfomicrobium strains, respectively, at a concentration of 7.0 mg/L. Under these conditions, the biogenic H2S concentration was reduced to 18 mg/L. Gravimetric and microbiological analyses were conducted in accordance with ASTM G31, GOST 9.913-90, and NACE TM0172 standards. The results demonstrated that, unlike individual reagents, synergistic composite inhibitor systems exhibit superior performance against both electrochemical and microbiological corrosion, indicating their strong potential for industrial application.