The Influence of Hexamethylenetetramine on the Corrosion Inhibition of Low Carbon Steel in Mixtures of Sulfurous and Phosphorus Acids Containing Fe(III) by IFKhAN-92 and KNCS Composition

Abstract

This article studies corrosion of 08PS steel in 2 M H2SO4, 2 M H3PO4 and their mixtures (t = 20–80°C). Addition of a mixture comprised of 4.5 mM IFKhAN-92, a triazole derivant, and 0.5 mM KNCS inhibits corrosion of low carbon steel in these media. The existence of Fe(III) in the solutions worsens steel protection by this composition of inhibitors. The most stable against the impact of Fe(III) cations are the solutions of H3PO4 or its mixture with sulfurous acid with high content of H3PO4. Addition of hexamethylenetetramine (0.20 M) to these media enables protection of low carbon steels in acid mixed solutions with high content of H2SO4 (up to 60%) containing Fe(III). Upon etching of steels or acid washing of steel equipment in the case of potential accumulation of Fe(III) salts in such media accelerating metal corrosion, H2SO4 + H3PO4 solutions are recommended containing up to 60% H2SO4 and IFKhAN-92 + KNCS + hexamethylenetetramine composition, since in such a solution steel corrosion is minimized due to its interaction with Fe(III) compounds.