PECULIARITIES OF CORROSION OF LOW-CARBON STEEL IN THE FLOW OF SOLUTIONS OF ACIDS OF DIFFERENT ANIONIC COMPOSITION CONTAINING IRON(III) SALTS

Corrosion of low-carbon steel in solutions of HCl, HCl + H3PO4, and H3PO4 containing Fe(III) salts is studied. In the systems involved, the corrosion of steel results from its reaction with the acid solution and Fe(III) salt. In the discussed media, partial reactions of anodic ionization of iron, cathodic reduction of H+ and Fe(III) cations are realized on steel. The first two reactions are characterized by kinetic control, and the latter is characterized by diffusion control. The accelerating effect of Fe(III) cations on steel corrosion in the media studied is predominantly due to Fe(III) reduction. Binding of Fe(III) cations into complex compounds with anions of the corrosive medium reduces the value of their diffusion coefficient (DFe(III)). The value of DFe(III) is maximum in the HCl solution and minimum in the H3PO4 solution. The rate of partial cathodic reduction reaction of Fe(III) is determined by the value of DFe(III). As a result, the accelerating effect of Fe(III) on the cathodic reaction and, hence, the general corrosion of steel in the flow of aggressive medium is most significant in the HCl solution and least significant in the H3PO4 solution.