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Cathodic Protection

Partially Sacrificed Anode Rod Partially sacrificed anode rod
Cathodic protection is accomplished in the glass lined water heater by using an auxiliary magnesium anode. Due to the relative position of magnesium to steel in the electromotive series of metals, magnesium will corrode, producing an abundance of electrons which flow (much the same an electrical current) to the exposed steel surface and maintaining it in the electro-negative state. As current flow takes place, the anode rod reacts chemically to corrode at a rate faster than the steel inner tank. This process stops tank corrosion by substituting the sacrificial magnesium anode rod in place of the steel tank. As long as the magnesium anode rod remains in the tank, in an active state, there will be no corrosion of the minute areas of exposed steel inside the tank.

Anode Rods

Depleted Anode Rod Depleted anode rod

The life of the anode, in turn, depends on water temperature, amount of water used, and the quality of the glass lining. However, the most important factor in the life of the anode rod is the water chemistry, the hardness or softness of the water. Water softeners contribute to the change in water chemistry. Indirectly, softened water acts to reduce the service life of the anode, since its current demand becomes drastically higher. Also, check the manufacture and installation date of the water heater.

Do not remove the anode rod from the water heaters tank, except for inspection and/or replacement, as operation with the anode rod removed will greatly shorten the life of the glass lined tank and will exclude warranty coverage. The anode rod should be removed from the water heaters tank annually for inspection and replaced when more than 6 inch of core wire is exposed at either end of the rod.

From time to time, questions are raised as to the use of the R-tech and magnesium anode rods. Generally, these questions are raised in areas where some unusual water problems occur with resultant odors. For many years, the regular magnesium anode was and is the standard anode for use in water heaters tanks. In general, it is a very good anode; however, the performance is dependent on water chemistry. In waters where the conductivity is low, the anode operates at a very low current level. This means not much cathodic protection. Conversely, where the water conductivity is high, an excessive amount of current is produced with inefficient operation. This will sacrifice the anode sooner than predicted and require more frequent replacement.

In addition, some of these waters have excessive sulfate content along with various strains of sulfate reducing bacteria (see Document 1206). These bacteria, harmless to health, will grow in the presence of the highly active magnesium anode rod and using the hydrogen ion from the anode-cathode reaction, will produce hydrogen sulfide gas. The gas smells like rotten eggs. The greater the activity of the anode, the more hydrogen ions are produced and the more hydrogen sulfide (smelly) gas. These bacteria can be killed with adequate additions of chlorine, such as with an automatic chlorine feeder.

The R-tech anode rod was developed to operate in a broad range of waters without the sensitivity to the various water conditions. This anode or a variation there of, has been used over 15 years in gas water heaters with minimal problems with odors. With the invention of the resistored electric heating element, Rheem now uses the Rtech anode rod in electric water heaters. In doing this, we are now able to efficiently utilize the R-tech anode in all type of water conditions.
Sourced From Rheem / Ruud - Technical Service Bulletin 1201.DOC