Copper Pipe Turns Green

[BAHTAH]

Have a customer who called because the copper water pipes in his house have turned green. Without getting into all that I found there was current traveling on the copper pipes. I have corrected that condition. Has anyone seen this happen and will the green slowly go away now that the current has been removed? Not sure if the current flow turns copper pipe green.

 

[mdshunk]

The green pipe has nothing to do with the fact that current was flowing on the pipe.

 

[charlie b]

The "Material Sciences" course that I was required to take in college was not my best friend, so I have very few facts to offer. I do know that when copper rusts, it turns green. What I do not know is whether current flowing through a section of copper can accelerate the rate of corrosion.

Were you able to detect and measure the current flowing in the pipe? Did it make the pipe feel hot to the touch? I believe that higher temperatures will accelerate the rate of corrosion.

 

[jjhoward]

I have been told that the phone company calls the DC current on their phone lines "sealing current". This is to help keep the copper to copper connections connected??

So maybe that current was keeping all that plumbing together.

 

[dereckbc]

It has nothing to do with current, it is a reaction from air and moisture called patina.

Initially, bare Cu metal atoms react with air to form the pink oxide, cuprite, Cu2O, which has Cu+1 cations. This gradually oxidizes further to the black oxide, tenorite, CuO, with Cu+2 ions. The black sulfide CuS also sometimes forms. In the presence of moisture, the blackish layer slowly reacts with sulfur dioxide and carbon dioxide from the air to eventually form the patina, which is a mixture of 3 minerals:

brochantite, a green, hydrated copper sulfate, Cu4SO4(OH)6
malachite, the green, hydrated copper carbonate Cu2CO3(OH)3
azurite, the blue, hydrated copper carbonate Cu3(CO3)2(OH)2

In these compounds, copper atoms from the metal surface have been fully oxidized into Cu+2 (cupric) ions. The rate of patina formation and the proportion of the components depend upon humidity and the amount of air pollution.

 

[480sparky]

So how much current is required to make a copper roof turn green?

 

[jjhoward]

Geez Dereckbc; Were you just waiting for that question??

Thank you for trip down memory lane to physics class!

I hope there won't be a pop quiz.

 

[wptski]

Okay, why would have one single wire going to a breaker box full of other breakers turn green?

 

[chris kennedy]

Okay, why would have one single wire going to a breaker box full of other breakers turn green?

It always wanted to be an EGC?

 

[Dennis Alwon]

Okay, why would have one single wire going to a breaker box full of other breakers turn green?

I have seen this happen. In my case the bare wire was next to the panel feed close to it's termination. The connection was loose and the jacket on the wire started melting and the bare copper wire had formed into the conductors insulation but had not shorted out (yet). The green color formed right where the bare conductor was almost touching the feeder.

 

[weressl]

The "Material Sciences" course that I was required to take in college was not my best friend, so I have very few facts to offer. I do know that when copper rusts, it turns green. What I do not know is whether current flowing through a section of copper can accelerate the rate of corrosion.

Were you able to detect and measure the current flowing in the pipe? Did it make the pipe feel hot to the touch? I believe that higher temperatures will accelerate the rate of corrosion.

'Corrosion' in the colloquial use is nothing else but an electrochemical reaction between two electrogalvanically dissimilar metal or metallic compound. Most common metallic compound is salt that is freely present all around as.

Any natural corrosion can be accelerated by the introduction of a potential differential. Have a potential differential and a conductive path and there is your completed circuit with the above detected 'current flow'.

Sometimes this current flow is intentionally induced to protect undergound metallic objects. This is called cathodic protection. The 'greening' of a copper pipe sure can be a sign of stray current and left alone long enough will create a piping failure.

 

[zog]

It has nothing to do with current, it is a reaction from air and moisture called patina.

Initially, bare Cu metal atoms react with air to form the pink oxide, cuprite, Cu2O, which has Cu+1 cations. This gradually oxidizes further to the black oxide, tenorite, CuO, with Cu+2 ions. The black sulfide CuS also sometimes forms. In the presence of moisture, the blackish layer slowly reacts with sulfur dioxide and carbon dioxide from the air to eventually form the patina, which is a mixture of 3 minerals:

brochantite, a green, hydrated copper sulfate, Cu4SO4(OH)6
malachite, the green, hydrated copper carbonate Cu2CO3(OH)3
azurite, the blue, hydrated copper carbonate Cu3(CO3)2(OH)2

In these compounds, copper atoms from the metal surface have been fully oxidized into Cu+2 (cupric) ions. The rate of patina formation and the proportion of the components depend upon humidity and the amount of air pollution.

Correct but current flow will accelerate the process.

 

[dereckbc]

Correct but current flow will accelerate the process.

DC current will but not AC current.

Weressi touched on one effect telephone company's uses or at least to use. Telephone battery plants use a positive ground reference. In the old days outside plant cables use to be lead sheathed. By referencing the positive terminal of the battery set up Cathodic Protection of the cables. By referencing the positive terminal instead of corrosion you actually build minerals around the cable. If you referenced the negative terminal to ground you would accelerate corrosion. CP does not work with AC.

Now with that said one known problem in telephone offices with battery plants is copper and steel pipes degrading which is seen as small pin holes and leaks. This is from DC current flowing in the structure.

The only way I know of for AC to have any effect on copper is if there is a difference of potential between two dissimilar metals like Aluminum contacting Copper.

 

[iwire]

Lets define the current flow we are talking about.

It seems obvious to me the current flow from one end of a copper pipe to the other will not promote the greening of the pipe, if that was the case all our conductors would be green.

On the other hand a copper pipe buried in the dirt with current flow between the pipe and the dirt it is contact with may accelerate the process.

 

[dereckbc]

From Copper.org

Recently I purchased sheets of copper and would like to know what I can put on the copper to prevent it from turning green or looking like an old penny. Can you tell me what product I should use to protect my copper countertops as well as the copper sheet behind my range?

One reservation you may have about copper is the material's tendency to turn green with age. Contrary to popular belief, this oxidation only occurs when the copper is directly exposed to outdoor elements or acidic conditions.

 

[dereckbc]

One more thought. Is there any galvanised clamps, fittings, or even a nail touching the copper any where? Just a single nail touching a copper line will cause a reaction. I know plumbers that have had to re-pipe whole homes from galvanized fittings being used.

 

[wptski]

I have seen this happen. In my case the bare wire was next to the panel feed close to it's termination. The connection was loose and the jacket on the wire started melting and the bare copper wire had formed into the conductors insulation but had not shorted out (yet). The green color formed right where the bare conductor was almost touching the feeder.

In my case, it was just one hot wire to one of the breakers. The entire end where the insulation was stripped was green except where the screw made contact. It was tight too.

 

[weressl]

DC current will but not AC current.

Theoretically this is correct. In practice the natural surrounding contains elements that DO act as semiconductors or diodes, so there is a small amount of the AC that leakes as DC. Not to mention the DC component that exist during arcing switching.

 

[dereckbc]

Theoretically this is correct. In practice the natural surrounding contains elements that DO act as semiconductors or diodes, so there is a small amount of the AC that leakes as DC. Not to mention the DC component that exist during arcing switching.

I agree with you but; DC (AC for that matter) current alone will not turn copper green or black. It takes a chemical or galvanic reaction to turn copper green or black. DC current can accelerate the process, but not cause the reaction. The root cause of the problem is chemical, not current.

My best guess is this is an enviromental condition like moisture (sweating/condensation on a cold water pipe), acidic, or mineral like iron or zinc in contact somewhere with the copper via soil or hardware. Heck if you have ever been in a barn all the copper is green or black from the amonia in the air from urine.

 

[weressl]

I agree with you but; DC (AC for that matter) current alone will not turn copper green or black. It takes a chemical or galvanic reaction to turn copper green or black. DC current can accelerate the process, but not cause the reaction. The root cause of the problem is chemical, not current.

My best guess is this is an enviromental condition like moisture (sweating/condensation on a cold water pipe), acidic, or mineral like iron or zinc in contact somewhere with the copper via soil or hardware. Heck if you have ever been in a barn all the copper is green or black from the amonia in the air from urine.

Absolutely as I have pointed out in my other post. Two metals with differences between their ionic characteristics and the presence of an electrolyte as Signore Luigi(not Mario) Galvani discovered it.:smile:

Or to put it another way; one's corrosion is another man's battery.:grin: