The green color is copper oxide, which is a form of
corrosion on the copper pipe, but unlike iron oxide (rust), it will not eat
through the pipe and cause a leak. The green spots are likely caused by moisture
in the air of your basement condensing on the surface of the pipe.
How do I get rid of the green on my copper pipe?
Wipe the pipe with a rag to dry the area and remove condensation.
Rub an emery cloth over the discoloration to remove the green coloring and reveal shiny copper. ...
Wet a rag with acetone. ...
Heat any persistent green sections with the flame from a propane torch.