Impressed Current Cathodic Protection For External Bottom Plates Of Large AST – Design Versus Factual Model

Maintaining a successfully operating Cathodic Protection to the entire surface of the tank bottom plate is a challenge to the practicing CP professionals.  Proper and even distribution of the CP current is one of greatest importance. Defining an adequate criteria for effective protection of such a system is a challenge, considering: high resistivity electrolyte (washed sand), limiting current density at anode surface to reduce depolarizing effects due to oxygen evolution by anodic reactions, tank surface temperature, etc. This case study is carried out for anode grid systems, which are commonly utilized for Cathodic Protection of AST bottom plates in the Middle East. Different technical solutions for arranging the anode grid on large diameter (90 m. dia) tanks are studied and compared in respect to the CP major objective. Attenuation of CP current in the anode appears to be one of the main factors for consideration at the CP design and understanding of the real structure model behavior is the one to be considered at the time of CP system operation and maintenance.