The following parameters are required in order to determine the current requirement:
- Type of coating of the storage tank bottom
- Operating temperature of the tank
- Surface area of the tank
- A factor included in the surface area accounting for the surface area of the welds between the tank bottom plates
- The type of anode you wish to use (assuming magnesium if it is a sacrificial anode system)
- The basic current density assumed, commonly considered as 22mA/m2
The basic idea is to multiply the surface area by the coating breakdown factor by the adjusted current density based on the operating temperature. Once you arrive at a current requirement, you can estimate the mass of anodes required based on the type of anode (consumption rate) and design life amongst other parameters.
I tried to provide you with the basics. However, you need to get your hand on a reliable cathodic protection handbook. There is more to it.
