CORROSION CONTROL OF BOTTOM PLATES IN ABOVE-GROUND STORAGE TANKS

A corrosion control system for an above-ground storage tank having a steel bottom plate comprises a sacrificial anode disposed under and spaced apart from the steel bottom plate in a backfill material, and wherein the backfill material has a pH high enough to cause a substantial passivation of the surface of the steel plate facing the sacrificial anode while substantially preventing the passivation of the sacrificial anode. In the preferred embodiment the backfill material has a pH of 10 or greater and the sacrificial anode is in the form of a plate or mesh composed of aluminum or an alloy thereof. Alternatively the sacrificial anode may be composed of zinc or an alloy thereof. The backfill material further includes soda ash, trisodium phosphate or other high alkaline chemicals to raise the pH. The backfill material also preferably includes a moisture retention material such as zeolite to maintain a minimum of moisture content of 10 percent or greater.