Nitrite corrosion inhibition in chloride-rich electrolytes correlated to the electrical properties of surface films on carbon steel

Abstract

The electronic properties and the composition of surface films grown in pore simulating solutions are studied using various electrochemical and surface techniques and then correlated to the inhibiting efficiency of nitrite ions in chloride-rich alkaline solutions. In nitrite-free and chloride-rich solutions, the external layer of the surface film is porous, defective and rich in Fe(III). Instead, when nitrite and chloride ions are simultaneously present, the Fe(II) content increases and the film becomes thicker, ordered and more protective. In the absence of nitrite ions, chloride ions induce high donor densities that correlate to a high susceptibility to localized corrosion. In contrast, the donor density decreases noticeably when nitrites and chlorides are both present and also increases with ageing time, reaching values comparable to those calculated for uncontaminated solutions.