When the tank is filled with water, an electrolytic process begins whereby sacrificial anodes are consumed to protect a small amount of exposed steel. Powered anodes replace that process with electricity and are not consumed.Electrolysis simply means that when two metals are physically connected in water, one will corrode away to protect the other. Although few people have heard of this, the principle is used all over the place — anywhere that someone wants to protect metal exposed to water. In marine applications, anodes are known as “zincs” and are usually made of that metal.
All metals fall somewhere on the galvanic scale of reactivity. When two are placed together in water, the “nobler” — or less reactive — one will remain intact while the more reactive one corrodes. When steel and copper are together, steel will be the one that corrodes. Indeed, steel is more likely to rust in the presence of copper than it would have been by itself. That’s why dielectric unions are necessary on items like copper flex lines when they’re connected to steel nipples.
Magnesium and aluminum are less noble than steel, which is why they’re used for anode rods.
Remember, the anode is screwed into the tank. That means it can be unscrewed and replaced.
A sacrificial anode’s life depends on the quality of water, the amount of use the tank gets, the water temperature, and the quality of the tank. When salt is added to the water (as in softened water), anodes corrode more quickly. Water softeners can help reduce sediment, but anodes can corrode in as little as six months if the water is over-softened. Do not soften to zero. Leave 50-120 ppm of hardness.
People occasionally ask us if pipe-seal tape applied to the threads of the anode blocks the electrolytic reaction. Tanks we’ve serviced repeatedly usually have corroded anodes. We’ve tested with a multimeter and found current flowing between the anode and the tank, despite the tape.
While we generally advocate putting two anodes in a tank, that may not be a good idea if you have odor problems.
Why We Don’t Like Aluminum Anodes – Go to http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater and select the ANODE link. This link talks about many important water heater tips.
Happy Camping,
Fred b.