Green Coating inside copper pipe

[Anonymous]

While replacing a failed water mixing valve (the valve reduces the temperature of the water coming from my hot water tank to the house), I noticed that the hot water copper pipe from the hot water tank to the mixing valve has a green coating INSIDE it (all along the length of pipe I removed). The cold water pipe did not have this, and the mixed pipe out of the valve has some green stuff, but not nearly as much. Does this mean that I have a corrosion problem, or is this normal? The piping is two years old.

[daveroconnParticipant]

Is this well water or city water?

[GuestParticipant]

Well water. The well water is quite hard (around 22 grains), but I have a water softener. Ph is 7. No copper in the well water. Fairly low levels of iron (my water softener will remove this).

[jbosloyParticipant]

Well water. I have a water softener (the well water is hard, around 22 grains). Ph is 7.

[daveroconnParticipant]

Free hydrogen ions found in all water to at least some extent provide a means of removing the excess electrons from the mass of metal. The electrons and the hydrogen ions react to first form atomic hydrogen, and then molecular hydrogen gas. As the hydrogen forms, it too tends to inhibit further corrosion by forming a very thin gaseous film at the surface of the metal. This “polarizing” film can be effective in reducing water to metal contact and thus in reducing corrosion. Yet it is clear that anything which breaks down this barrier film tends to increase the rate of corrosion.

Dissolved oxygen in the water will react with the hydrogen, converting it to water, and destroying the film. High water velocities tend to sweep the film away, exposing fresh metal to the water. Similarly, solid particles in the water can brush the hydrogen film from the metal.

Water temperatures. High water temperatures not only accelerate the chemical reactions of corrosion, but also may reverse normally protective systems.

The removal of hardness with an ion exchange water softener does not affect the factors, which cause or accelerate corrosion. Softening does not change the pH or carbon dioxide concentration, the dissolved oxygen concentration, or the total chemical concentration of minerals. A softener may reduce the amounts of solid particles in the water, but obviously cannot change other physical factors such as temperature, flow rates through pipes, or volumes of water used. Thus ion exchange softening neither causes nor controls corrosion.

Respectfully David F. Walling

[jbosloyParticipant]

Thanks for the info. When I fill up a sink with hot water, I see lots of tiny bubbles in the water, and it takes a whiile for the water to look clear. The cold water does not do this. Is there any system that can remove dissolved oxygen or other gasses from well water to reduce this problem in a cost-effective manner?

[daveroconnParticipant]

The simple answer is to allow the water to off gas before it’s pressurized and run into your plumbing. This would be done with a large atmospheric storage tank or (break tank). You should use an automatic chlorinator to disinfect the water after the storage tank. This will also oxidize any of the iron making it easy to filter out.

Remember you are dealing with your drinking water and should have a basic understanding of water chemistry. This may not be the solution for your water without seeing any test results or the configuration of your system.

Respectfully David F. Walling

[jbosloyParticipant]

Thanks. I am having trouble finding anyone local who knows about installing break tanks (or atmospheric storage tanks). Could you reccommend a manufacturer of such a system so I can look into this some more?

[Author]

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