WHY COPPER PIPES GET RUSTY?
Corrosion Copper Pipes
Copper pipes are often used in newer properties. Until some time ago, copper pipes were considered the ultimate among water pipe materials. In the meantime, multilayer composite pipes or the cheaper variation normal plastic pipes have been installed.
Compared to the even older iron pipes, copper pipes have the advantage of having much smoother inner surfaces. As a result, they offer the lime considerably less attacking surface. This smooth surface results in significantly less incrustation in copper tubes.
Ideally, a thin film of lime will form on the inside of the pipe to protect the copper from corrosion. But if there is too much calcium carbonate in the water, copper pipes can also become clogged with lime over time.
CORROSION
If, on the other hand, there is too little lime in the water, i.e. the water is considered soft. Then a protective layer can only form to a much lesser extent. This can also lead to corrosion in copper pipes. If the water stay in the pipe for a longer period of time, the oxygen begins to gas out. This might be another reason for corrosion.
Copper oxide (CuO or more rarely Cu2O) is formed and the copper reacts with the oxygen dissolved in the water. If large quantities of copper oxide have formed in the pipes, this often leads to a slightly greenish discoloration of the water. Any limescale deposits, e.g. on aerators, may also have the greenish shimmer typical of copper.
Metal impurities in the water can lead to contact corrosion. This happens, for example, when rust particles from the public water network get into the water pipe. The rust particles and the copper form a galvanic element, which in the worst case leads to pitting. Nothing else then a pinhole leak in the water line.
Same is true for pipes. The corrosion might lead in the end to so called pinhole leaks in the piping network. If there are pinhole leaks one have to do plumbing and repair the pipe. Either replace the piece of pipe with the leak, or close the leak. If one has access to the leak a plumber can solder the pipe. Shrink hoses are some times an option as well.