A 10,000 barrel bolted tank was found to have developed active internal corrosion within an eight year period. The tank was then coated on inside bottom and two feet up on the shell with a coal tar product, and steam coils were installed. After 12 years’ additional service it was found that four leaks had developed in the tank. It was again cleaned, the steam coils removed, and the tank visually inspected. Welded repairs were made to the tank and the coating was repaired. Four 9 pound magnesium anodes were installed at this time and 6 inches of water were placed in the tank to serve as electrolyte. Anodes were installed so that they could be inspected or replaced while the tank was in service; records were made of anode outputs, driving potential, anode efficiency and tank-to-electrolyte potential. Current outputs were restricted and the 9 pound anodes ultimately were replaced with 17 pound anodes.
A measured output of 666 ampere-hours/pound was obtained from one of the 9 pound anodes. It is calculated that four 17 pound anodes would last 3 to 4 years, with more than ample current when restricted with a 1 ohm resistor. Tank to electrolyte potential at the last reading measured —0.4 volts to iron reference electrode.
Control was obtained by utilizing a 5 foot x 7 foot test tank filled with one foot of electrolyte from the 10,000 barrel tank.
