Effect of Ozone on Corrosion of Metals Used in Cooling Towers

The effect of dissolved ozone on the corrosion of mild steel, copper (Cu), 90 Cu-10 Ni (nickel), 70 Cu-30 Ni, and admiralty in typical cooling tower waters with different solute contents was studied using electrochemical techniques. Results showed ozone at typical usage (0.1 to 0.2 mg/L) had no significant effect on the anodic passivation of mild steel. In general, corrosion in the presence of ozone was dictated by water chemistry. In supersaturated solution, general corrosion was suppressed by a layer of insulating mineral scale on the surface, regardless of the presence of ozone. In some solutions, however, high localized corrosion rates were observed both when ozone was present and when ozone was absent. In solution with low levels of Ca2+ and HCO3–, corrosion rates much higher than industry standard were observed with or without ozone. In a non-scaling, medium hardness water, ozone generally increased the corrosion rates of all yellow metals, especially at high concentration or under conditions with high mass transfer rate. The presence of 1 mg/L ozone had the greatest corrosive effect on Cu, with lesser effects on 90 Cu-10 Ni and 70 Cu-30 Ni and even less effects on admiralty.