Current and potential distribution modeling for cathodic protection of tank bottoms

Aboveground tanks for the storage of liquid hydrocarbon are often erected with a secondary containment membrane installed below the tank bottom to prevent soil contamination in case of leakage. The design of impressed current cathodic protection in the presence of the plastic membrane is based on distributed anodes installed in the space between the tank bottom and the membrane; among available anodes, the most commonly used are the titanium grid or ribbon activated with noble metal oxides. The configuration of the grid or ribbon anode system confined in the closed space between the bottom and membrane creates specific issues concerning the electrochemical reactions occurring at the anode and cathode, the ohmic drops in the anode system, and the potential and current distribution at the cathode. Results of a number of numeric simulations performed to predict the actual distribution of current and potential are given. Design criteria are discussed.