Inhibitory protection of steels in hydrochloric and phosphoric acid mixtures containing Fe(III) salts

• Ya.G. Avdeev¹, L.V. Frolova¹, A.V. Panova¹, K.L. Anfilov² and Yu.I. Kuznetsov¹

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

Abstract: The effect of the IFKhAN-92+KNCS+urotropine composite inhibitor (molar ratio of components 9:1:400) on the corrosion, hydrogen absorption and retention of plastic properties of high-strength steel 70S2KhA in solutions of a HCl+H₃PO₄ mixture containing Fe(III) salts was studied in the temperature range of t=25–60℃. The high efficiency of the composite inhibitor in inhibiting the corrosion and hydrogen absorption of this steel and retention of its plastic properties was shown. In these media with a content of Fe(III) salts up to 0.10 M, addition of 4.5 mM IFKhAN-92+0.5 mM KNCS+200 mM urotropine slows down the corrosion of high-strength steel significantly, the maximum metal corrosion rate being 1.7 g/(m²·h). No hydrogen absorption of steel at t=25 and 40℃ is observed, both in the absence and in the presence of Fe(III). Only at 60℃ was weak hydrogen absorption (1.0 cm³/100 g) observed, but it decreased with an increase in the content of Fe(III) in the inhibited solution. After exposure of steel samples to these media, the plasticity of the metal is close to that in the as-delivered state if the Fe(III) concentration does not exceed 0.05 M. Moreover, the formulation of IFKhAN-92, KNCS and urotropine in HCl and H₃PO₄ solutions containing Fe(III) prevents the corrosion and hydrogen absorption of low-carbon steel 08PS. In industrial operation of inhibited HCl solutions, if there is a potential for the accumulation of Fe(III) salts, which significantly reduces the efficiency of steels protection in these media, solutions of HCl+H₃PO₄ mixtures inhibited with the formulation of IFKhAN-92, KNCS and urotropine are recommended as an alternative. In such inhibited solutions of acid mixtures, efficient protection against corrosion and hydrogen absorption of high-strength and low-carbon steels is retained even if up to 0.1 M Fe(III) is accumulated in them. High-strength steels retain plastic properties in such environments.

Keywords: acid corrosion, corrosion inhibitors, high strength steel, low carbon steel, hydrogen absorption of steel, hydrochloric acid, phosphoric acid, iron(III) chloride, iron(III) phosphate

Int. J. Corros. Scale Inhib., 2020, 9, no. 3, 1084-1096 PDF (486 K)
doi: 10.17675/2305-6894-2020-9-3-19

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