Tom-
Reference my post on 1 Feb 04 and your reply. Using your procedure, I have determined electrolysis is not the problem. Had 0 current readings. While Michigan is fairly high humidity, at times, I don't think that is the cause of the problem because other homes in nearby locations have not had the same "blackening". A local Master Plumber is also puzzled about the problem. Do you know of a plumbing or similar organization that would evaluate a short section I could remove? Any other idea you might have would be welcome.
CharlieK

I know of no plumbing shop shop that can run a analysis on your copper pipe. A testing lab would have to do that. What I would is take some sandpaper and bare a stretch of copper and monitor it to see what happens. It really doesn't sound to me that you have all that much to worry about. If you find and pit marks get back to me. Good luck, Tom