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White Rust

The term white rust refers to a type of corrosion product affecting the galvanized surfaces of a cooling tower. White rust is an accumulation of white, fluffy or waxy, non-protective zinc corrosion product which adheres to the zinc surface of galvanized steel. White rust is indicative of rapid corrosion of the galvanized coating. If it is not controlled, early failure of the cooling tower will result.

White rust most often occurs in new cooling towers. It is possible, however, to have white rust occur in older towers as well. To prevent white rust, the galvanized coating must be "passivated". Cooling tower water maintained within the following parameters for 45 to 60 days will passivate the galvanized coating.

  • Maintain pH in the range of 7.2 to 8.0. Do not allow total alkalinity to exceed 300 mg/l
  • Maintain calcium hardness in the range of 100 to 300 mg/l.
  • Maintain chlorides less than 450 mg/l
  • Maintain sulfate less than 1200 mg/l
  • Watcon 113P is specifically designed for white rust prevention. Maintain 6 to 10 mg/l of orthophosphate in the tower water using Watcon 113P
  • Biological control is extremely important. Tower surfaces must be kept deposit free
  • Automation of bleed, inhibitor addition, biocide addition, and pH control will facilitate operating the tower under these conditions.
After the 45 to 60 day period, a treatment program tailored to the specific application should be employed.
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Watcon, Inc. 2215 South Main Street
South Bend, IN 46613