At the turn of the century, the first indoor plumbing involved the use of lead pipes. These were replaced later with cast iron and by 1940 galvanized plumbing became the standard. Galvanized plumbing is made of steel with a galvanized interior, which makes the pipe more resistant to corrosion. It has now been replaced by the use of copper and plastic pipe.
Galvanized plumbing has a life expectancy of about twenty years depending on use and maintenance. After about 30 years, galvanized pipe with an interior diameter of half an inch can be reduced to a very small opening because of corrosion and buildup of lime, scale and rust.
Rust is easy to recognize in water quality. It turns the water a shade of red, orange or yellow. If leakage, rust or low water pressure is evident, the galvanized pipes are corroding internally and should be replaced either with copper or plastic pipe. The most effective way to establish the condition of the inside of galvanized plumbing is to remove a sample of pipe. By cutting out a small stretch of pipe it is easy to see how the interior walls are holding up and how much buildup there is. This is usually done on a horizontal stretch of pipe where water has an opportunity to sit stagnant. Vertical pipes are generally in better interior condition because gravity tends to keep them free of still water and debris.
Dark stains on the outside of the pipe do not necessarily indicate internal corrosion. Condensation around the pipe can cause flaking or staining, but is less likely to corrode the pipe from the outside in. Homes built before 1970 with galvanized pipes can expect to be in need of replumbing. Galvanized piping is still available but is seldom recommended for use.
Another tell-tale sign of wear is the presence of compression patches. Often when the pipe begins to rust out the leak is patched rather than replacing the pipe. A compression fitting is two pieces of metal with rubber seals and screws. They are tightened around the leaking pipe. It is easier to fix a leak in galvanized plumbing in this manner than to try to cut out the leak and replace it because it is almost impossible to create a threaded joint on a rusting pipe.
When galvanized pipes are connected to each other the joints are screwed consisting of threaded ends and couplings. Galvanized plumbing can be joined to plastic or copper pipes. When copper is used, a bi-metallic fitting is necessary.