One of the major dangers for any metal appliance that comes into contact with water is corrosion. This chemical reaction when water meets metal in the presence of oxygen will rapidly weaken the metal to the point that it flakes away. Yet water heaters—large metal appliances that are in constant contact with water—very rarely develop rust until the end of their services lives.
How water heaters resist the destructive effects of corrosion? One of the secrets is a crucial component called the anode rod, also known as a sacrificial anode rod for reasons that will become clear when you learn about how they work.
The noble sacrifice of the anode rod
An anode rod is a metal rod that is made of magnesium or aluminum around a core of steel wire. The rod is attached to the top of the water heater tank, and extends down through stored water. Through a complex electromechanical process, the anode rod starts to corrode instead of the steel walls of the tank.
The simple way to explain the process: When two metals are connected to each other through water, the less reactive of the two metals (i.e., the more “noble” of the metals) will remain untouched by corrosion while the other corrodes. In the case of a water heater, the magnesium of aluminum of the anode rod are less noble than the steel of the tank, so rod corrodes instead of the steel. Basically, the anode rode “sacrifices” itself to rust away before the more noble steel of the tank, hence the alternative name. It’s almost… chivalric in a way.
The corrosion of the anode rod eventually destroys it, and when that happens nothing will prevent the steel of the tank from corroding. The anode rod needs to be replaced on a regular basis in order to keep the water heater healthy. The amount of time it takes for an anode rod to decay varies, but you should have it checked once a year during a routine maintenance visit from a water heater professional. The maintenance technician will let you know when the anode rod needs to be replaced.
To arrange for service for your water heater, call on the experts at Modern Plumbing Industries, Inc. (MPI) in Orlando, FL.