Definition - What does Copper Corrosion mean?
Copper corrosion is the corrosion of materials made of copper or copper alloys. When exposed to the atmosphere, copper oxidizes, causing bright copper surfaces to tarnish. After a few years, this tarnish gradually changes to dark brown or black, and finally to green.
Copper corrodes at negligible rates in unpolluted air, water and deaerated non-oxidizing acids. However, it is susceptible to more rapid attack in oxidizing acids, oxidizing heavy-metal salts, sulfur, ammonia, and some sulfur and ammonia compounds.
Pitting failure occurs in cold-water copper lines that conduct aggressive well waters. Copper is susceptible to crevice corrosion attack.
Corrosionpedia explains Copper Corrosion
Certain conditions can cause copper to corrode when it is exposed to particular soils, including:
- Abnormally aggressive soils
- Localized and long-line-type concentration cells created by differences in soil composition
- Action of stray direct currents (DC) flowing in the ground
- Faulty design and workmanship
- Certain conditions created by alternating currents (AC)
- Thermogalvanic effects
- Galvanic action involving dissimilar materials
Coupling of copper with aluminum or copper with steel can lead to severe galvanic corrosion. Cyanides are also very corrosive to copper pipe.
The good resistance of copper pipe alloys to corrosion by seawater depends partly upon the inherent cathodic nobility of the metal, but it also depends on the ability to form protective films. High-velocity and turbulent flow conditions can remove these films and permit local, rapid corrosion.
There are two types of copper corrosion:
- Uniform - Identified by the presence of a relatively uniform layer of copper corrosion byproducts across the inner surface of a pipe wall. It is typically associated with elevated copper levels at the taps.
- Non-uniform - Isolated development of corrosion cells across the inner surface of a pipe wall. Excessive pitting corrosion can lead to pinhole leaks in the pipe. This can result in water damage and mold growth.