Up until the 1950s, galvanized steel (sometimes referred to as "iron pipe") was the most common plumbing pipe being used. So when you're looking at a house that's more than 40 years old, you can be pretty certain that it will have at least some amount of galvanized steel piping. And the older the home is, the higher its probability of pipe problems.
The average life span of galvanized steel piping is approximately 40 years but that estimate largely depends upon the acidity and mineral content of the water. The main failure method of galvanized piping is to rust from the inside out.
The rusting that occurs on the inside of the pipe is a chemical reaction. As with most chemical reactions, rusting tends to move faster with higher temperatures. That's why the pipes carrying hot water are usually the first to fail.
The early signs of failure usually show up as weaker pressure and flow on the hot side when compared to the cold. Failure usually occurs at the threaded connection, which makes sense because the pipes are thinner at the threads due to material being removed to create them. (See the diagram below).
It is worth noting that while the reduction pressure and flow might an indicator of early galvanized piping failure, there are many other possible causes of the reduced flow. Here are a few that come to mind:
- Loss of pressure resulting from elevation gains (three-story houses are worse than one-story homes).
- Private water systems that can't build up enough pressure in the system.
- Installed whole house water filtration or treatment equipment.
- An older water heater that might have sludge in the tank that is adversely affecting the pressure on the hot water side of the system.
In summary, when I inspect a greater-than-40-year-old house, I expect to find at least some galvanized steel piping. And if in a house with galvanized steel piping I also find a reduction in pressure flow, I always recommend further evaluation of the plumbing system by a licensed plumber.