Anode rods are used to protect exposed tank metal from corrosion. If two different
metals are in contact with each other and water, the less "noble" of the two metals
will corrode first. Once the first metal is completely eaten away, the second metal
will begin to corrode.
The anode rod is sometimes called a "sacrificial anode," because it is sacrificed to
protect the steel of the tank. If the anode is never allowed to completely dissolve, it
will continue to protect the tank. (Figure 2-25)
Another approach to tank wall protection is to apply a thick lining of low sulfur
cement to the inside. After the tank is baked, a thick stone lining completely covers
the tank walls. This lining is very hard to break.
Normally, no anode rod is used on stone lined tanks. This eliminates one
maintenance step. However stone lined tanks weigh around 50% more than glass-
lined tanks. (Figure 2-26)
Stone lined tanks are readily available in standard sizes of 40 to 120 gallons. Most
manufacturers offer tanks with an internal heat exchanger coil.
STEEL TANK WALL
2.7 COMPONENT OPERATION