Effect of Fe(III) salts on the protection of low carbon steel in hydrochloric acid solutions by some corrosion inhibitors

The effect of Fe(III) salts on the protection of 08PS low carbon steel in 2 M HCl and 2 M H3PO4 at 20 and 60°C by corrosion inhibitors (PKU-E, Catapin A, Catapin BPV, Soling m. Z, Soling m. L, VNPP-2, Invol-2 m. A and NORUST CM 150 C) and their mixtures with hexamethylene¬tetramine (HMT) has been studied. None of the individual and two-component corrosion inhibitors studied can provide efficient protection of steel in HCl and H3PO4 solutions if significant amounts of Fe(III) cations are accumulated in them. In H3PO4 solutions containing Fe(III) phosphate, efficient protection of steel can be obtained by the formulation comprising 2 g·L–1 VNPP-2 + 0.5 mM KNCS + 200 mM HMT as the corrosion inhibitor. The same formulation protects steel in 1 M HCl + 1 M H3PO4 (20 and 60°C) with up to 0.10 M Fe(III) cations accumulated in it. Solutions of a HCl + H3PO4 mixture inhibited by the formulation of VNPP-2 + KNCS + HMT can be an alternative to inhibited solutions of individual HCl in case of potential accumulation of Fe(III) chloride in them.