Corrosion inhibition of low-carbon steel in the flow of a mixed-acid solution containing Fe(III) salts

• Ya.G. Avdeev and T.E. Andreeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: The corrosion kinetics of 08ps low-carbon steel was studied in static and dynamic 1 M HCl+1 M H₃PO₄ solutions containing Fe(III) salts (up to 0.1 M of Fe(III) cations) in the temperature range of 20–60°C. The empirical dependence of the corrosion rate of 08ps steel on the rotational speed of the propeller stirrer used to provide forced convection of the corrosive medium is described by the equation k=k_st+λ·w^1/2, where k_st is the corrosion rate of low-carbon steel in the static medium, w is the rotational speed of the propeller stirrer, and λ is a coefficient characterizing the increase in the corrosion rate of the steel. A formulation comprising a mixture of 10 g/L VNPP-2MV (corrosion inhibitor)+200 mM hexamethylenetetramine (HMT)+0.5 mM KNCS was studied as a corrosion inhibitor for 08ps steel in this medium. This formulation in the media under study provides satisfactory protection of the steel in both static and dynamic solutions at 20–60°C. The solution containing a mixture of HCl and H₃PO₄ with the addition of VNPP-2MV+KNCS+HMT can be used as a chemical cleaning agent for removal of mineral deposits from the surface of low-carbon steels. Relatively low corrosion rates of the steel are maintained in this solution even upon accumulation of up to 0.1 M Fe(III) cations. The maximum corrosion rate observed does not exceed 7 g/(m²·h), even under flow conditions.

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

Int. J. Corros. Scale Inhib., 2026, 15, no. 3, 286-300
doi: 10.17675/2305-6894-2026-15-3-12

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