Ruud(Page 1 of 3)
TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
Anode Rods, Cathodic Protection and the Porcelain (glass) Lining
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 waters ability to corrode:
- Acidity - Water is made acidic by naturally occurring dissolved gases such as carbon dioxide.
- Temperature - Higher temperatures speeds up the corrosive process.
- Amount of dissolved oxygen - Free oxygen dissolved in the water promotes corrosion.
- 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
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.Sourced From Rheem / Ruud - Technical Service Bulletin 1201.DOC