Development of a phosphoric acid-based chemical formulation for cleaning low carbon steel that is resistant to the accumulation of iron(III) salts

• Ya.G. Avdeev¹, A.V. Panova², T.E. Andreeva¹, K.L. Anfilov³ and Yu.I. Kuznetsov¹

¹ Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia
² CJSC GIAP-DISTcenter, 4-4, Serebryakova proezd, 129226 Moscow, Russia
³ Federal State Autonomous Educational Institution of Higher Education “Bauman Moscow State Technical University”, 5-1, 2-ya Baumanskaya st., 105005 Moscow, Russia

Abstract: The corrosion of low carbon steel of grade 08PS has been studied in solutions: 1 M H₂SO₄ + 1 M H₃PO₄ + Fe(III) salts and 1 M HCl + 1 M H₃PO₄+Fe(III) salts (60°C) containing three-component mixtures as metal corrosion inhibitors: 2 g/L Inhibitor + 0.5 mM KNCS + 200 mM HMT (Inhibitor = GREENCOR m. V, INVOL-2 m. A, VNPP-2-V and VNPP-2MV; MT = hexamethylenetetramine). It has been shown that the lowest corrosion rates of steel (no more than 2.0 g/(m²·h)) are observed in 1 M HCl + 1 M H₃PO₄ with the inhibitor mixture 2 g/L VNPP-2MV + 0.5 mM KNCS + 200 mM HMT, even in the presence of Fe(III) salts with concentrations up to 0.10 M. The chemical formulation: 1 M HCl + 1 M H₃PO₄ inhibited with the mixture: 10 g/L VNPP-2MV + 0.5 mM KNCS + 200 mM HMT, has low corrosivity towards 08PS steel in the temperature range of t=20–80°C with up to 0.10 M Fe(III) salts accumulated in the mixture. The corrosion of 08PS steel in 1 M HCl + 1 M H₃PO₄ (20°C) inhibited by this mixture is characterized by low corrosion rates (up to 1.8 g/(m²·h)) and weak sensitivity to the convection of the corrosive medium with up to 0.10 M Fe(III) salts accumulated in the medium. Taking the experimental results into account, a chemical formulation based on phosphoric acid for cleaning low carbon steel from mineral contaminants that is resistant to the accumulation of Fe(III) salts is recommended. The formulation contains 1 M HCl + 1 M H₃PO₄ as the acid component. The corrosion inhibitor protecting the steel is a mixture of VNPP-2MV + 0.5 mM KNCS + 200 mM HMT. This chemical formulation can be used both under static and dynamic conditions of metal cleaning. Static solutions can be used at temperatures up to 80°C, inclusive.

Keywords: low carbon steel, acid corrosion, corrosion inhibitors, phosphoric acid, hydrochloric acid, iron(III) phosphate, iron(III) chloride

Int. J. Corros. Scale Inhib., 2025, 14, no. 2, 628-643
doi: 10.17675/2305-6894-2025-14-2-11

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