[anne-marie]

Hi!
I have a big corrosion problem on copper piping.
To make a long story short, they're installed in a highway pumping plant,
so the environment should not be corrosive that much (beside deicing salt
in winter and tons of cars and trucks passing by), but it's very humid.
All the copper used in the same area formed a thick black flaky deposit
on it. If I scratch the surface with a knife, it comes off relatively easily
and the copper underneath it is free of the usual greenish corrosion. If I
take off isolation foam or an identification sticker (acting as protection
in this case), the pipe is as good as new, but it have been installed 30
years ago! According to archives, this deposit have begun with a sudden
change of the pipes color (usual red to purple) and then became black with
time, all this within 1.5 years. The chemical analysis of the deposit revealed
the presence of sulphur. Even if they're installed in a highway rain pumping
plant, no rain water should ever get through these pipes because they're used
only for domestic water inside the plant. Ventilation ducts (zinc galvanised
steel) have no problems, neither than aluminum electrical components. Brass
fittings have medium problem: black deposit, but it looks like primer paint on it.

Thanks a lot for your *delete me*

[Arkcon]

Your previous statement contains no question. 

I'm guessing this black coating is copper oxide, despite the sulfur content you noted, though it could be copper sulfide from local environmental conditions.

As I recall, copper goes through a variety of strange oxides on it's path to it's final lovely verdigris color.  People in the US were quite upset back in the '80's when the refurbishing of the Statue of Liberty marred it's surface for a time.

What is the problem with this corrosion?  Is the pipe failing or likely to fail?  And are you sure it isn't just flaking paint, like you suspect the black stuff on the fittings is?

[Navik]

Hello,

I have totally same problem.
Have you found what the cause of black corrosion was?

Thanks!