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?

How Long Will Pipe Last?

Steel pipe and tubing rusts!  Any material made with iron that is exposed to water and oxygen is going to rust.  How fast the pipe will rust depends on a multitude of variables - humidity, temperature, rainfall, pollution, type of soil, and more.  We'll skip the detailed discussion of the electrochemical process!!  Instead, we'd like to share what we've learned from a few decades of experience with the pipe and tubing that we sell here. 

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Generally for new pipe:

• 14 Gauge pipe left outside and unprotected will rust through in 30 years.

• 11 Gauge pipe left outside and unprotected will rust through in 40 years.

• 9 Gauge pipe left outside and unprotected will rust through in 48 years.

Paint stops or significantly slows down rust!  If you take away the exposure to water or oxygen, the rust process will cease or proceed very slowly. Painting protects the pipe.  Pipe that has been protected with paint will last a lifetime.

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Used pipe rusts much quicker.  The chemicals and fluids that the pipe have been exposed to create crevices and pitting deep into the metal.  Frequently sections of the pipe are paper thin.  Used pipe that has been threaded or collared rusts faster since the threads create thin spots in the thickness of the pipe.

Decoiled pipe (which is also used) has been rejected because of metal fatigue.  The continuous bending and straightening creates thin spots which cause it to rust much faster.