Anodic Passivation of Steel In 100 Percent Sulfuric Acid

The feasibility of anodic protection for decreasing iron contamination of 100 percent sulfuric acid in an 18,000-gallon steel storage tank was investigated. Since adequate coatings for steel in this service are not available, this approach was taken as an alternative to costly equipment replacement with corrosion resistant alloys. Preliminary laboratory testing indicated that the corrosion rate of steel in 100 percent sulfuric acid could be reduced from 27 mpy to 1 mpy by anodically passivating. As this represented a substantial decrease in terms of iron contamination of the acid, a plant test was run using anodic protection on the storage tank. Passivation of the tank resulted in lowering the iron pickup from 114 ppm down to 9 ppm with trouble-free operation of equipment over a seven-month period. It was concluded that anodic protection offered significant economic advantages compared to the use of more resistant materials of construction.