Effect of the anionic composition of acidic solutions containing Fe(III) on the protection of low-carbon steel by a triazole inhibitor

Abstract

The corrosion of low-carbon steel 08PS in 2 М HCl, 2 М H2SO4, and 2 М H3PO4 solutions as well as in their mixtures at t = 20–80°C has been studied. Addition of a mixture of the IFKhAN-92 inhibitor, which is a triazole derivative, with KCNS slows down the corrosion of the low-carbon steel in these media. The presence of Fe(III) in the solutions weakens steel protection by the inhibitor formulation studied. The presence of phosphates in an acid solution decreases the adverse effect of Fe(III) as it binds Fe(III) cations into strong phosphate complexes. This effect is most distinct in H3PO4 and H2SO4 + H3PO4 solutions with high H3PO4 content. A mixture of IFKhAN-92 and KCNS forms a polymolecular inhibitor layer on the steel surface. This layer can efficiently slow down the reduction of Fe(III) phosphate complexes. In steel etching or in cleaning of steel equipment in acidic solutions, where Fe(III) salts are accumulated and accelerate steel corrosion, it is recommended to use solutions of H3PO4 or its mixtures with H2SO4 (at least 50%) inhibited by a formulation of IFKhAN-92 with KCNS.