Protection of aboveground storage tanks against corrosion

Both sacrificial anodes and impressed current system are used for cathodic protection of aboveground storage tanks. In this method, the protection of the inner surface of the tank is done by the method of sacrificial anodes and the protection of the outer surface of the tank floor is done by ribbon MMO anodes. Because the tank has large dimensions and therefore high weight, to support the weight of the tank, ribbon anodes with a flat cross section are used. Also, flat anode will lead to better flow in the tank floor. Before placing the bottom and body of the tank in the desired location, first the anodes are installed in the correct way, then a special layer of sand is poured on it and finally the bottom of the tank is placed on the sand.

Cathodic protection of the tank floor

The impressed current cathodic protection system is placed in the bottom of the tank in such a way that first the ribbon MMO anodes are laid in the form of horizontal strips in the bottom of the tank and in order to connect the anodes to the rectifier, the conductor bar which are titanium strips without cover, are used perpendicular to ribbon anodes. The connection of titanium bar to ribbon anodes is done by spot welding. The negative phase of the rectifier is connected to several points of the tank body. The positive phase of the rectifier is connected to a junction box and then through it, titanium bars is attached to the anode. The job of titanium is to deliver current to the anode. These connections are well done in different places so that no interruptions occur. Also, a number of permanent reference electrodes  are placed on the bottom of the tank so that the potential of different parts of the tank can be measured.

In the past, other methods were used to cathodically protect the tank around it, such as drilling wells and placing anodes around the tank. But these methods did not bring the flow evenly to the bottom of the tank.

Cathodic protection inside the tank

The ribbon anodes inside the soil only protect the outer surface of the tank floor from corrosion. Because there is a different electrolyte inside the tank, such as water or crude oil, other anodes must be used to protect the inside of the tank. Sacrificial anodes, and in some cases impressed current anodes, are commonly used to protect the inner surface of the tank. Inside the crude oil tanks, only the sacrificial zinc anode is used.