I'm renovating my bathroom. I ripped out the floor and I noticed that there is a green deposit on the outside of the copper tubing. Is this a problem? Do I need to have a plumber check it out? The pipes are 50 yrs. old.
The green deposit forms as the copper of the tubing chemically combines with other elements on the nearby environment. The presence of wetness or water can accelerate the formation of the greenish copper compound.
I have seen multiple instances where the acidity of the water sitting and flowing inside the pipe can eat the pipe walls thin from the inside over many years. This can lead to pin hole leaks in the pipe that lets small droplets of water come out and produce corrosion of the pipe like seen here. It would be well worth checking out this area of the copper pipe to see if there is a pending disaster waiting to happen.
That normally means there was a water leak at some point. If you look at the pipe on the left in your picture, you can see a small trail coming down from up above. Is there any sign of water above the floor/cabinet? A small amount of green on copper usually isn't anything to worry about. You just want to make sure that whatever is leaking has stopped.
If there is still a leak, clearly you'll need to fix that.