The influence of different variables on the electrochemical behavior of mild steel in circulating cooling water containing aggressive anionic species

Cyclic voltammetric, potentiodynamic anodic polarization and current-time transient studies were carried out on mild steel in circulating cooling water containing Cl- and SO (4) (-2) ions under the effect of different variables such as coolant flow, the availability of oxygen, cooling system temperature, and cooling system pH. The anodic excursion span of mild steel in cooling corrosive solution was characterized by the occurrence of a well-defined anodic peak (A1), while the reverse sweep was characterized by the appearance of two cathodic peaks (C1 and C2). The presence of Cl- and SO (4) (-2) ions in cooling water enhance the active dissolution of mild steel and tend to breakdown the passive film and induce pitting attack. The data reveal that increasing flow rate and temperature of cooling solution enhances the anodic peak current density (j (A1)) and shifts the pitting potential (E (pit)) towards more active values. It is seen that the peak current density of the anodic peak A1 increases and the pitting potential (E (pit)) displaced in the noble direction in the aerated solution compared that in de-aerated solution. The pitting corrosion of mild steel by Cl- and SO (4) (-2) ions initiates more readily in acidic medium (pH 2.0). It was found that the incubation time (t (i)) increase and in turn the pitting corrosion decrease in the order: pH 10 > pH 6.8 > pH 2.0.