As the name infers, this plumbing product was used in attempts to reduce or inhibit rusting. And that it does. However these pipes are not rust proof.
Galvanized pipes are usually found in homes over 50 years in age. Commonly, these pipes will rust from the inside out. The pipes can corrode at any time however this rust accumulates over decades. Sometimes if the water is not in use and then turned on you can see that the water is brownish in colour or that fixtures have become rust stained.
Although the water pressure can be reduced the volume of water is often restricted too from the rusting. This occurs as a result of the pipe rusting on its interior and becoming smaller and smaller over time. Eventually the pipe becomes blocked or worse yet bursts. Ultimately these pipes must be replaced as they have a life span of about 50 years.
It is important to note that some insurance companies are now refusing to provide home owner's insurance on houses with this type of plumbing.