How to Replace an Anode Rod

TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
1-800-432-8373
Anode Rods, Cathodic Protection and the Porcelain (glass) Lining
Technical Competence, Product Confidence
Page 1 of 5
1201.DOC
Corrosion can be defined as the destructive attack of a metal by an electrochemical reaction with its
environment. Steel exposed to moisture and oxygen will rust and corrode. Corrosion is defined as the ‘eating away’
of metal by electrochemical means. There are four main factors affecting water’s ability to corrode:
1. Acidity - Water is made acidic by naturally occurring dissolved gases such as carbon dioxide.
2. Temperature - Higher temperatures speeds up the corrosive process.
3. Amount of dissolved oxygen - Free oxygen dissolved in the water promotes corrosion.
4. Electrical conductivity - The more dissolved mineral solids in the water, the greater its ability to carry
electrical current. When dissimilar metals are in the water:
• Electrical current flows between metals
• One of the metals gradually corrodes faster than the other
Dissimilar metals are present in the interior steel tank surfaces of all water heaters in several forms such as
the drain nipples, heating elements, inlet and outlet nipples, and immersion thermostats. These metals, and others
present in the water itself, combined with the oxygen content of the water and heat, establish an environment
conducive to corrosion. The dissimilar metals create a corrosion cell that is enhanced by the conductivity of the
water. The anode is installed to overcome (neutralize) the corrosive cell.
The Porcelain (glass) Lining
In a water heater, corrosion is protected by a glass (actually a porcelain enamel) lining in the steel tank, and
the use of auxiliary anode rods. Porcelain enamel begins as a blend of minerals mixed in a manner to form liquid
slurry. This slurry, resembling a thin mud, is sprayed onto the inner surfaces of the water heaters. During the
manufacturing process, the inside water tank and both the top and bottom heads are sprayed with a slurry of glass
material. After the tanks are sprayed, they are fired at very high temperatures - generally ranging from 1500 to 1600
degrees Fahrenheit. While in the furnace the porcelain bonds with the metal to create more than a coating. It forms
an inseparable compound merging the chemical makeup of the porcelain glass lining and metal resulting in a new,
chemically unique finish. This glass
provides a long life to the steel tank;
otherwise, the tank would fail or corrode
in a relatively short time. Every glass lined
water tank, no matter how carefully it is
manufactured, has some microscopic bare
metal areas exposed to the water inside the
tank. There is a chance that a crack or
chip in the porcelain lining will allow the
water to come in contact with the steel
tank. Over time, water, a universal solvent
that becomes more aggressive with
temperature, slowly dissolves the interior
tank lining. This will create conditions for
corrosion, pinholes in the tank and finally
tank failure.
(Microscopic view of steel and porcelain
lining after firing)