The general thinking is, any plumbing from the '60s or older is on its last legs. That's because most of the piping used pre-1960s was galvanized steel. In fact, if you are looking at a house from that era or earlier, chances are it probably has had so many problems that it's already undergone substantial re-plumbing. But in case they have not been fixed before, the two top plumbing concerns you are likely to find in most old houses are broken pipes or low water pressure and there’s a good chance you can blame galvanized pipes. Although they can be found in some homes even younger than that. Back then, it was believed that coating metal pipes with a thin layer of zinc would help prevent corrosion. However, as it turns out, galvanized pipes developed all kinds of problems over time and are now commonly replaced with copper or plastic piping.
Disadvantages of Galvanized Pipes
Internal Rusting - Although the zinc barrier in galvanized pipes does prevent rusting for a certain amount of time, it eventually wears out. When this happens, your pipes begin to corrode from the inside out, which can eventually lead to a leak or a broken pipe.
Unstable Joints - The threaded joints that connect galvanized pipes are often unstable and prone to leaks and rusting. Often the threaded joints wear at the zinc coating of the pipes, which can quickly expose the metal underneath and cause corrosion.
Water Contamination - When galvanized pipes begin to corrode, the corrosion materials and lead from exposed metal can seep into your water supply. This compromises the quality of your home’s water and can even change its color.
Mineral Buildup - The zinc coating in galvanized pipes reacts with the minerals in your water supply. When this happens, those minerals begin to form a plaque that coats the inside of your pipes. Over time, that plaque begins to restrict your home’s water flow.
For a quick test of an old house, turn on the hot water. If the pressure is low, the house probably has galvanized pipes that have corroded and plugged up. The hot-water pipes are the first to go. The house could have good pressure in the hot-water lines, but still have unseen galvanized-pipe problems. It is possible that only the bad pipes were replaced, leaving lots of old galvanized pipes still in the house and either in need or soon-to-be-in need of replacement.
Experts will tell you to replace the entire piping system when galvanized piping starts to go bad, but that is pricey, and often homeowners opt for the more economical, halfway fix by repairing only the pipe that is the immediate problem. Worse, the bad galvanized pipe may have been replaced with more galvanized pipe instead of copper or plastic pipe, meaning the problem has just been extended, rather than fixed. It's diff
icult to determine the entire plumbing picture, since most of the system is behind walls. Look under the sinks to get some understanding -- often, plumbers run new pipes up through the floor under the sink instead of through the wall, so you can see where there is new plumbing. If the house has a crawl space and you're not too discomfited by going into it, you can get a better picture of the plumbing status.
Anytime copper piping has been attached to galvanized pipes, dielectric coupling is required to stop the corrosion caused by dissimilar metals touching. A dielectric union pipe fitting is designed to hold two types of metal pipe together, without actually soldering them. With a copper and an iron pipe, this is necessary as the combination of metals under solder could produce galvanization, leading to corrosion and failure of the pipe. Dielectric union fittings provide a plastic bar between the two pipes, breaking the galvanized current and preventing the pipes from corroding. This helps to preserve the pipes for a longer period of time, and also avoids accidental creation of electricity. In addition to this, the dielectric union pipe can also serve as a quick pipe union joint. A coupling of two pipes would require welding, or rotation through a thread coupling which would involve turning the pipes together. With a dielectric union pipe, you can join the pipes together quickly, and also release them quickly.