Control of Couples Developed in Water Systems

The presence of copper and its alloys in water systems complicates control of the corrosion of the ferrous metals present with inhibitors. The solution of copper by the water on passage through the cuprous portions of the system and its subsequent deposition on the ferrous metal portions develops couples which are particularly difficult to control with inhibitors. A solution to this problem is offered by 2-benzothiazolethiol which can inhibit attack on copper and its alloys to an extent such that negligible copper is dissolved by the water. The factors involved in the use of this material in conjunction with the glassy phosphate inhibitors for steel were investigated. It was found that 2-benzothiazolethiol showed a tendency to interfere with many glassy phosphates used to protect iron and steel; when the compound was used in connection with Calgon T this was not the case.