Current and potential distribution modelling for cathodic protection of tank bottoms

Above ground tanks for storage of liquid hydrocarbon are often erected with secondary containment membrane installed below the tank bottom to prevent the soil contamination in case of leakage. The design of impressed current cathodic protection in 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 bottom and membrane creates specific issues concerning the electrochemical reactions occurring at anode and cathode, the ohmic drops in the anode system and the potential and current distribution at the cathode. The paper shows results of a number of numeric simulations performed to predict the actual distribution of current and potential. Design criteria are discussed.