Copper pipes gone black, clean or replace?

[cmpic]

Hi all,
I had the house redone about 1.5 yrs ago and all new plumbing was installed. I have plastic pipes in general except copper pipes in the cellar where the boiler and water tank are. The copper pipes have now turned black but the black layer comes off with sandpaper or emery paper. I've identified two sources of potential oxidation 1- sparkies fit three stainless steel earth clamps to a copper pipe run (Scalebuster fitted which needed to be grounded), and 2- plumber left an uncapped drainage pipe for a future sink (possible that sewer gas was causing corrosion though there is no strong bad smell in the cellar). I've now capped the open drain pipe and will replace the stainless steel earth clamps. From here onwards - can I just clean the oxidation off the pipes and bronze fittings with some steel wool or emery paper and leave as is or do I now have to replace everything? Thanks for the advice!

 

[SimonG]

Probably damp, any ventilation down there?

 

[cmpic]

Probably damp, any ventilation down there?

Passive only. There is about 60-70mm vent hole to outside but for many months during winter it was closed off (I have since opened it). The heat of the boiler/tank keep it about 19-22C year-round. The cellar is tanked (Delta membrane) with two sump pumps in the ground. It may be a bit humid but doesn't feel particularly so right now (will put a gauge to measure). Also both gas and cold water pipes have turned black (both have stainless steel earthing clamps) whereas hot water pipes seem to be unaffected - but they are also not directly connected to the cold pipes.

 

[Chuck]

2- plumber left an uncapped drainage pipe for a future sink (possible that sewer gas was causing corrosion though there is no strong bad smell in the cellar).

I think you've probably found the problem. H2S, a component of sewer gas, is very corrosive and turns copper pipe black/purple even at relatively low concentrations. Bronze fittings are similarly affected but stainless steel is relatively immune.

 

[cmpic]

Thanks Chuck. Though this drainage pipe leads to the container of the sump pump and is not directly connected to the general sewage pipes. The more I think of it the more I think that SimonG may be right, that this is caused by condensation/humidity. Why else would cold water and gas pipes be affected and not the hot water pipes?

Could humidity cause such an issue?

 

[Chuck]

Could humidity cause such an issue?

Corrosion is complicated and it's not impossible.

Condensation in unpolluted air is essentially dilute carbonic acid. Typically, exposed copper gets progressively darker brown then changes to dark green after a couple of years. After that it gets lighter over the next couple of decades.

You've given a textbook description of H2S/SO2 corrosion so it may be worth widening your search for a source. It's a bit of a stretch but do you have any damp plaster board, or a domestic waste bin, or a compost heap in the vicinity? All of these can evolve H2S and not much of the stuff is required to cause corrosion.
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OTOH, it's a bit surprising that, if the cause is H2S, the hot pipes weren't similarly affected...

 

[Christian]

I'am seeing New copper lines in the unfinished basement, just noticed that a length of both, hot and cold have turned black. The sump pump has a constant flow of water to it, could it be that causing the problem? Also it does have water softener being a on a well system, could that be the the problem? No drywall in basement. House is around 2 years old. Any suggestions??? Thanks