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.