Copper Metals Exceptional Resistance to Corrosion
One of the most outstanding and certainly the most complex features of copper metals is their corrosion resistance. Corrosion is usually defined as a deterioration or failure of metal by chemical or electrochemical processes. However, since corrosion is a reaction of a metal’s surface to its environment, deterioration does not take place until the corrosion penetrates the surface.
All copper metals react quickly to their environment and form a film of surface oxidation. However, this tarnish, or patina, affects only the appearance and not the matrix of the metal. Therefore, the metal itself does not deteriorate. It is protected by the surface oxidation, which is generally not soluble in water, and which adheres tightly to the surface, preventing exposure to further environmental corrosion. In effect, the extremely long life of copper metals is due mainly to the fact that their oxidized surfaces protect them from further deterioration.
Copper metals offer excellent resistance to industrial, rural, and marine atmospheres. Dry atmosphere way from the seacoast will produce the least surface discoloration, while industrial and marine atmospheres will produce maximum coloration.
Fresh water exposure: Copper tubing is commonly used for fresh water piping.
Sea water exposure: Many copper alloys are used for sea water applications, C122, C443, C444, C445, C614, C655, C687, C706, C710, and C715.
Steam exposure: All copper metals are resistant to attack by pure steam, but if there is much carbon dioxide, oxygen, or ammonia present, the steam condensate may be harmful.
Sanitary drainage: Copper tube (alloy 122) generally gives excellent service for residential drainage.
Soil corrosion: According to tests by the National Bureau of Standards, copper and copper alloys having low or no zinc content offer excellent resistance to soil corrosion.
Dezincification: Acidic water which comes into contact with copper metals containing 15% or more zinc causes dezincification. Here both the copper and the zinc are leached out of the metal by the acid.
Electrolytic corrosion: This can occur under two different conditions. One, called galvanic action, is contact between dissimilar metals in the presence of an electrolyte. The other occurs when an outside current of electricity passes through an electrolyte from a copper metal.