Inhibition of carbon steel corrosion and hydrogen penetration into the metal in media containing H2S and CO2

Abstract

The efficiency of EM-9 product as a versatile inhibitor against carbon steel corrosion and hydrogen penetration into the metal in slightly acidic chloride-containing media (pH = 2 – 4; 50 g/l NaCl) containing hydrogen sulfide and carbon dioxide separately and in combination has been investigated. The EM-9 formulation is a process mixture of polyaminoimidazolines, products of the reaction of tetraethylene pentamine with tall oil acids. The bactericidal properties of the inhibitor have been investigated. The bactericidal ability of the inhibitor with respect to sulfate reducing bacteria (SRB) was estimated by two methods: i) reduction in the number of the microorganisms, ii) retardation of H2S formation by the microorganisms (iodometric titration). The inhibitor favors the preservation of the mechanical properties of St3 and 65G steels under the same conditions and slows down the hydrogen diffusion across a St3 steel membrane. The latter was evaluated in an electrochemical hydrogen permeation Devanathan-type cell. The qualitative correlation between the slowdown of hydrogen diffusion through the steel membrane by the inhibitor and the preservation of the mechanical properties of steel in the presence of the inhibitor has been shown. The mechanical properties of steel have been estimated under conditions of stretching and bending stress after corrosion tests in uninhibited and inhibited solutions for 24 hours. Thus, EM-9 is a versatile inhibitor that slows down the corrosion of carbon steel and hydrogen penetration into the metal in media containing H2S and CO2 separately or in combination. It shows a high bactericidal activity and the ability to preserve the mechanical properties of steel.