Cathodic Protection of Steel Water Tanks Using Aluminum Anodes

Aluminum alloy anodes have been used in approximately 1,000 installations of cathodic protection of steel water tanks using current from an outside source. From fundamental considerations it would be expected that the loss in weight per ampere hour of current passed from aluminum anodes would be less than one-third the weight loss from steel anodes. This addition, it was found that the aluminum anodes developed a more uniform attack than did anodes of steel or stainless steel. This is desirable because localized attack can result in early anode failure. The corrosion products from the aluminum anodes are white or colorless and adhere to the anodes. In the case of anodes of many other metals the corrosion products are strongly colored and fall off the anodes, thus discoloring or otherwise contaminating the water. Anodes of several aluminum-base alloys all have proved satisfactory in field installations. However, anodes of the aluminum-copper alloys (such as 17S-T or 24S-T) appear to be superior to anodes of unalloyed aluminum (2S) or to aluminum-zinc alloy anodes.