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wkingkick, Building Inspector
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Why do copper water pipes turn blue on the outside?

Customer Question

Why do copper water pipes turn blue on the outside?
Submitted: 4 years ago.
Category: Home Improvement
Expert:  Eric M. Bright replied 4 years ago.

Hi, Welcome to, I am glad you are here! My name is Eric & I will endeavor to answer your question.


There is nothing dangerous or destructive happening when your copper pipes turn Green / Blue neither are they deteriorating.


Nignthoujam Sandhyarani ties it up very nicely as follows:

Copper oxidizes whereby it turns Blue / Green. Oxidation is a phenomenon whereby an element loses electrons (and/or hydrogen) on interacting with another element. There are many examples of oxidation, which we observe in our day-to-day life. To mention a few; there is oxidation of iron, aluminum and even, a freshly cut apple.

Oxidation of iron, referred to as 'rust', leads to corrosion and/or formation of a flaky, reddish outer layer. Another example is the oxidation of aluminum, leading to formation of white, flaky layer. This is usually seen in aluminum doors and windows after a heavy rainfall. When an apple is cut and the cut surface is exposed to air, it turns brown. This is nothing but oxidation.

Similar to iron and aluminum, the element copper undergoes the process of oxidation, if it is exposed to air. Copper metal reacts with oxygen, resulting in the formation of copper oxide, which appears green in color. It is to be noted that copper does not react with water. The outer green layer, formed after the oxidation of copper, is known as patina.

Unlike other destructive oxidation, patina acts as a protective layer. This is the reason as to why, copper is considered as an important metal, resistant to corrosion. The patina prevents further corrosion of copper beneath the oxidized layer. Very often, patina is seen on the roofs of old buildings, which acts as a waterproofing layer.

The function of patina as a protective layer can also be seen in the Statue of Liberty. According to the Copper Development Association, the oxidation of the statue's copper skin is only about 0.005 inch till now. For preventing oxidation, the best way is to protect the surfaces, that are likely to be exposed to air and water, with the help of a protective coat. This way, the surface of the metal is prevented from reacting with oxygen and/or water.



Expert:  Stephen Cutler replied 4 years ago.
The reason you see it on copper pipes AT the fittings, is because the plumbers use acid flux to "eat" oxidation off the pipe prior to sweating the joints. Crappy/lazy plumbers leave the acid on the pipe and it oxidized the pipe at an acclerated rate. Plumbers who are particular about their work wipe the pipe with a damp rag while the pipe is still hot. This removes the acid. You can tell what kind of plumber did the work on your pipes by how clean they are. The pipes should be a fall leaf brown and uniform in color throughout. But don't freak out just because you have an installation with excessive oxidation at the joints. Even with accelerated oxidation by acid, it will be 20-30 years before the joint begins to leak. If you have exposed joints that exhibit acid exposure, you can still clean the acid off with dishsoap & a scrubby sponge. My point is that discoloration at the fittings is not the normal oxidation rate. It is evidence of failure to clean joints after sweating, and does rise to the level of panic. If you live in a climate that has reactive soils, AND your copper plumbing runs under a slab on grade, you will need to have the dwelling repiped sometime between 20-30 years after the date of construction. This is VERY common in FL.
Expert:  wkingkick replied 4 years ago.
Besides the corrosion that is taking place hat everyone is telling you about, you might find it even stranger to find that the water could actually turn blue as well. Many people feel that the change in color is from electrolysis which occurs when two different metals touch each other. This may be the case if correct connectors are not used. The simple fact is that all new copper pipes dissolve at a rate of .001-.003 per inch, per year during the first few years of installation. Soft water conditioner, accelerated rate of copper dissolving possibly due to a low ph level below 6.5. One other strange event that began after the EPA Safe Water Act of 1991 when the NOM's began being removed from the water. It caused a lack of the protective patina which occurred when copper begins to dissolve.

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