Inhibitory protection of low carbon steel in a flow of phosphoric acid solution containing iron (III) phosphate

The corrosion of low carbon steel in a flow of H3PO4 solutions containing FePO4, including media with additives of mixture of corrosion inhibitors consisting of a 3-substituted derivative of 1, 2, 4-triazole (IFKhAN-92) and KNCS, was studied. In the discussed medium, 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 last one is diffusion-controlled. The accelerating effect of FePO4 on steel corrosion in a H3PO4 solution is mainly due to the reduction of Fe (III). In inhibited acid, the accelerating effect of Fe (III) cations affects all partial reactions of steel. Despite such an accelerating effect, the mixtures of IFKhAN-92 and KNCS retain a high inhibitory effect on the electrode reactions of steel, which is an important result. The data on corrosion of low carbon steel in the flow of the studied media, obtained from the mass loss of metal samples, are in satisfactory agreement with the results of the study of partial electrode reactions. The accelerating effect of FePO4 on steel corrosion in the flow of H3PO4 solutions, including in the presence of inhibitors, is noted. In these media, steel corrosion is determined by the convective factor, which is typical for processes with diffusion control. Mixtures of inhibitors IFKhAN-92 + KNCS provide significant slowdown of steel corrosion in the flow of H3PO4 solution containing FePO4, which is the result of its effective slowdown of all partial electrode reactions of the metal.