"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 bare metal
exposed. This is due to the inability to
effectively cover sharp corners and the
radius around the fittings. 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 inthe tank
I found this on a RHEEM WEBSITE
http://www.houseinspections.com/PDF_LINKS/anode%20Rod.pdf"
