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

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 (60C) 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; HMT=hexamethylenetetramine).It has been shown that the lowest corrosion rates of steel (no more than 2.0 g/(m 2 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 =20-80C 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 (20C) inhibited by this mixture is characterized by low corrosion rates (up to 1.8 g/(m 2 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 80C, inclusive.