Galvanized pipe life expectancy

Question

USA, NW Oregon, single-story house with crawl space, built 1972.

Background

The house has the original galvanized piping in the crawl space and suffers from low water flow in two bathrooms. Static pressure measured at an external hose faucet near where the service line enters is 80psi so pressure is not a problem. The kitchen, which is next to the service line entry, does not have a flow problem

The home inspector suggested the galvanized pipe is near the end of its service life. An additional factor is that that the previous owners did a major remodel of the kitchen and both bathrooms 5-7 years ago and installed copper risers (yay, no sheetrock tearout to repipe) but the contractor didn't use dielectric couplings, which could have accelerated corrosion in the galvanized pipe near the joints. When I replaced the shower heads I found some black crumbly granules in the old shower heads, and also in a sink aerator.

We have decided to replace the galvanized pipe with PEX, and there is some disagreement among contractor bids about the necessity of replacing the galvanized service line from the meter to the house. One contractor thinks it is not necessary.

Questions (all related):

1. Is the expected lifetime of galvanized pipe in the 40-50 year range as claimed by the inspector?
2. Could the lack of dielectric couplings have greatly accelerated the corrosion leading to the current situation?
3. If yes, would the copper be corroded/weakened as well?
4. Is there a way to inspect the service line to determine if it needs to be replaced?

Answer 1

1. 40-50 years is a fair lifespan. I've seen plenty of houses with galvi that was 60+ years old without it failing, the real issue to me is if you want to wait until it fails to replace it.

2. Not greatly accelerated the process, no.

3. Yes.

4. Potentially and at decent expense. It depends on the size of the water service, condition of the piping, and access point.

If you're re-piping your house and don't mind them digging up your yard, a water service replacement is a good idea. It should be cheaper to do it all at once rather than to do them as two separate projects.

Answer 2

Galvanized pipe can last a long time, without "failing". However, while the pipe might look great on the outside, the inside is likely restricted by corrosion and deposits. All galvanized pipe I've ever removed, looks something like this on the inside.

My advice to anybody that still has galvanized pipe in their homes, is to replace it as soon as possible.

Answer 3

Galvanic corrosion occurs when galvanized steel is in direct contact with copper and creates pin holes in the copper from the inside out. Copper does not degrade the steel pipe. What does happen inside the steel pipes is rust/mineral deposits form on the interior walls much like arterial buildup in a human being restricting your water flow. Because the buildup increases as water velocity decreases, you end up with a situation like yours where the plumbing fixtures near the water supply entry having a higher gpm than the fixtures further away from the entry point (the actual physical distance between the entry point and fixtures is irrelevant, the determining factor is the length of pipe between the two points).

Unfortunately, I'm in the southeast so I can't offer an opinion on the cost of the quote as we have completely different geological conditions and building practices.