Corrosion Resistant Copper & Plastic TanksBack to Article Index...
Benefits of Copper Tanks & Our Non-Pressure Plastic Water Heaters...
Performance and durability of water heaters depend largely on the water quality. Therefore it is essential to use the most suitable material for the inner (tank) container. Corrosion of any material is influenced by the operating conditions, type of installation and the chemical composition of the water. As water quality varies from place to place there are different kinds of water that can cause (promote) corrosion, while other types of water inhibit (prevent) corrosion.
Water that Causes Corrosion
This type of water is characterized by a low total hardness (referred to as soft water) with a high salt content (chlorides & sulphates) & a high content of oxygen and carbon dioxide. Corrosion causing water is called aggressive water & with aggressive water quality only water heaters with corrosion resistant or corrosion protected containers can be used.
Water that Inhibits (Prevents) Corrosion
This type of water is harder than the above mentioned. They contain less oxygen and carbon dioxide and can form a protective lime, calcium & rust layers in conjunction with galvanized steel. This protective layer only forms at temperatures of approx. 65°C, but at higher temperatures corrosion damage can occur depending on the type of material used. Water at low temperatures entering a hot tank (while large quantities of water are draw-off quickly) promotes the formation of a “natural” protective layer which inhibits corrosion.
Corrosion normally occurs to metallic materials used in water heaters. It is largely dependent on the material used in its construction, the corrosive quality of the water & the heating temperatures reached, plus the frequency of use. Electrochemical (Electrolysis) corrosion occurs when two different types of metals come into contact in a conductive liquid; this forms a conductive ability depending on the salt content in the water & leads to localized corrosion or pitting, thus destroying the base material (metal) of the tank. This can be caused by copper pipes which are connected to galvanized steel containers or by steel pipes, which are connected to copper containers, as rust develops in the steel pipes it flows with the water & sits in the copper containers.
Materials Used for Hot Water Appliances
Corrosion is avoidable to a large extent when specific basic rules regarding the selection and installation of the water heaters container and pipe materials are observed. Containers or Tanks for water heaters are made of either of corrosion resistant materials like copper or plastic, but larger units normally have enamel coated steel (tanks) containers, to protect against corrosion.
Stiebel Eltron can thus offer a Life–Time guarantee against corrosion on our copper and polypropylene (plastic) tanks, as these materials do not naturally corrode. These types of tanks do not need a “sacrificial” anode for protection against corrosion.
Corrosion Protected Materials
Large water heaters with steel (tanks) containers normally have an enamel layer coated on the inside & are thus adequately protected against corrosion. This special enamel consists essentially of silicate but other ingredients included are boron, fluorine, potassium and sodium (etc). This special enamel is hard, shock-proof, temperature-resistant, physiologically harmless and is neutral to all pipe materials. Pressure type enamelled tanks are available on our SHD 30 / 100 S models. The enamel layer is extremely resistant against abrasion – it is about 100 times as resistant against abrasion as the standard bath–tub enamel. Despite great carefulness slight irregularities in the enamel layer may occur. These defective spots, which at first are invisible, are protected against corrosion by an additional built-in anti-corrosion sacrificial anode. The anti-corrosion anode consists mainly of magnesium, and the SHD 100 ACS model has a warning light on the front indicating when the anode needs to be replaced. This will depend mainly on the quality of the water & operation temperatures, but replacing the anode will extend the life of the unit in most cases.
The Best Corrosion Resistant Material
The best corrosion resistant material is copper. Storage heaters with copper tanks (inner containers) are corrosion resistant against all known types of water & temperature resistant plastics have also proved to be a suitable material for tanks (containers) of non-pressure type storage water heaters. Stiebel Eltron has been producing non-pressure water heaters with plastic containers since 1972. The container is made of polypropylene & is totally corrosion resistant, and compared with copper it has lower heat conductivity and is much lighter in weight.