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

• Ya.G. Avdeev¹, A.V. Panova¹ and K.L. Anfilov²

¹ A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation
² Bauman Moscow State Technical University (Kaluga Branch), Bazhenov str. 2, 248000 Kaluga, Russian Federation

Abstract: The effect of Fe(III) salts on the protection of mild steel 08PS in 2 M H₂SO₄ 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) has been studied. None of the individual corrosion inhibitors studied can provide efficient protection of steel in H₂SO₄ and H₃PO₄ solutions if significant amounts of Fe(III) salts 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 hexamethylenetetramine as the corrosion inhibitor. The same formulation protects steel in 1 M H₂SO₄+1 M H₃PO₄ (20 and 60°C) with up to 0.10 M Fe(III) cations accumulated in it. Solutions of an H₂SO₄+H₃PO₄ mixture inhibited by the formulation of VNPP-2+KNCS+hexamethylenetetramine can be an alternative to inhibited solutions of individual H₂SO₄ in case of potential accumulation of Fe(III) sulfate in them.

Keywords: acid corrosion, low carbon steel, sulfuric acid, phosphoric acid, iron (III) sulfate, iron (III) phosphate, corrosion inhibitors

Int. J. Corros. Scale Inhib., 2024, 13, no. 2, 1135-1145
doi: 10.17675/2305-6894-2024-13-2-26

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