The copper plumbing pipe in my 4 year old home is turning black. Much of it is hidden in the ceiling of a finished basement. I suspect electrolysis, and have discovered a copper line touches a steel natural gas supply line. Since the contact area is so small, I don't want to draw a rush conclusion.
I have separated the two with rubber insulation. If in fact that is the cause will the corroding cease, or now that it is started will it continue and eventually cause plumbing leaks-----my greatest nightmare.

Are there other possibilites for this blackened appearance? Your opinions will be greatly appreciated.
CharlieK

Hey Charlie, I have had copper pipes turn black due to corrosion, high humidity and moisture. Also when copper tarnishes it will first turn green and then black. So electrolysis isn't the only culprit. With electrolysis look for pits in the pipes that will eventuality turn into pin holes. The method I use to check for electrolysis is to take a AC voltmeter and connect one lead to earth ground, (a pipe the goes under the basement floor) and set my meter on 110 vac. I then put the other leat on the suppected pipe and began to back down the meter settings. ANY READING you get indicates current is flowing and you, indeed, have electrolysis. You might want to remove the rubber insulation while you check so the pipes are back in the original configuration. You can then start insulating until you no longer get a reading. Good luck, Tom