Corrosion issues with bonding

[mikoal]

During an insepection there were 2 copper pipes, one carrying hot water and one carrying cold. However the cold water pipe is all corroded and green.

The inspector believes that this might be from the bonding (which is also copper), but he believes its from leakage current.

What are some possibilities of a pipe corroding and not the other. (i assume both of them are bonded).

Is a leakage current possible? If so what tests would be done in order to verify leakage current? can you use a clamp? or megger or???

 

[bphgravity]

I don't believe it is anything electrical at all. If the cold water pipe frequently condensates, or is located in a high-humidity area, atmospheric conditions will cause corrosive and/or surface contaminants to be applied to the copper pipe's surface.

 

[mikoal]

I don't believe it is anything electrical at all. If the cold water pipe frequently condensates, or is located in a high-humidity area, atmospheric conditions will cause corrosive and/or surface contaminants to be applied to the copper pipe's surface.

Thanks gravity.
But just to humor me, what tests are there for us to check whether or not there's leakage current?

There also exists a hot water pipe that is not corroded at all, in the same environment, atmosphere etc.

Also why would you rule out anything electrical?
I know there are corrosion issues with non similar metals (this is not the case)
Couldn't current potentially cause something similar to the metal to metal contact, enhance the corrosion?

EDIT: I also read in some instances if power cables are near the pipes, it can induce eddy currents that causes electrolysis. How likely is this? and What can we do to test?

 

[mikoal]

Thanks gravity.
But just to humor me, what tests are there for us to check whether or not there's leakage current?

There also exists a hot water pipe that is not corroded at all, in the same environment, atmosphere etc.

Also why would you rule out anything electrical?
I know there are corrosion issues with non similar metals (this is not the case)
Couldn't current potentially cause something similar to the metal to metal contact, enhance the corrosion?

EDIT: I also read in some instances if power cables are near the pipes, it can induce eddy currents that causes electrolysis. How likely is this? and What can we do to test?

In addition to what I wrote. I was told that since it is a copper water pipe, any condensation caused by the water will no corrode the pipe.

In the NEC should both the hot and cold pipe be bonded?

Looking at the picture it is only that pipe that is covered in green, the rest is fine. Also once it goes to a unioned section the corrosion is gone and there is no dielectric coupler or anyrthing.

I'll try ot attach a picture below.

 

[richxtlc]

The corrosion (patina) that you see is what happens when uncoated copper is exposed to the environment. The original coating may have deteriorated from the constant condensation.

 

[bphgravity]

The corrosion (patina) that you see is what happens when uncoated copper is exposed to the environment. The original coating may have deteriorated from the constant condensation.

I agree. Think of the Statute of Liberty. She hasn't always been green...

 

[mikoal]

The corrosion (patina) that you see is what happens when uncoated copper is exposed to the environment. The original coating may have deteriorated from the constant condensation.

I agree. Think of the Statute of Liberty. She hasn't always been green...

Thanks I will let the mechanical engineer know.
Do you think that temperature of the water plays a part to how much it condenses? because its only that pipe.

Also just to satisfy my curiousity, what type of tests are recommended to determine if there is any current leak from ground, and current on the pipe itself? Thanks!

 

[Paul Polakoff]

Hello

I would look at the panel box. The nuetral and grounds should only be common at the main panel box. ( first means of disconnect.) If nuetrals are touching grounds in any other box than the return currents may chose not to follow the nuetral and decide that going to ground where they touch each other is a path of least resistence. If the ground connection to the water pipe is the least resistence, than a current flow could be seen on that connection.

Some times people mistake that neutrals and grounds are to be kept seperate after the service. And in no case can they become bonded together again after the service. People many times use a ground wire as a nuetral in a box. The return currents have no choice but to use a ground path to make the device work. This is very dangerous and will cause corrosion.

Paul

 

[don_resqcapt19]

I can't see how current could cause a corrosion issue on the outside of the pipe.

 

[skeshesh]

I can't see how current could cause a corrosion issue on the outside of the pipe.

I agree. What are the temperature deltas in that area (delta between the ambient temp and the temp of your hot water and chilled water runs)? I've heard this issue brought up but most credible people I've talked to reject the idea. I've talked to a couple of mechanical engineers about it but they don't think its the case either. Obviously they're not experts on electrical issues (nor do I consider myself one) but some of them do have longer experience as far as mechanical engineering than I have experience breathing, and they've said that if that was a known issue they would have encountered it.

 

[zbang]

How about condensate on the cold water pipes mixing with concrete dust? Sulfates in the concrete combine with water to make sulfuric acid, which attacks copper to make copper sulfate. I'm not going to work the chemical reactions on this.