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

The effect of Fe(III) salts on the protection of mild steel 08PS in 2 M H 2 SO 4 and 2 M H 3 PO 4 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) has been studied.None of the individual corrosion inhibitors studied can provide efficient protection of steel in H 2 SO 4 and H 3 PO 4 solutions if significant amounts of Fe(III) salts are accumulated in them.In H 3 PO 4 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 hexamethylenetetramine as the corrosion inhibitor.The same formulation protects steel in 1 M H 2 SO 4 +1 M H 3 PO 4 (20 and 60°C) with up to 0.10 M Fe(III) cations accumulated in it.Solutions of an H 2 SO 4 +H 3 PO 4 mixture inhibited by the formulation of VNPP-2+KNCS+hexamethylenetetramine can be an alternative to inhibited solutions of individual H 2 SO 4 in case of potential accumulation of Fe(III) sulfate in them.