Green corrosion on copper waste pipe

Any ideas what would cause this corrosion and if it poses a risk of damage to the pipe.
It was only within about 6 feet of where the pipe exited the foundation. The rest of the pipe had no corrosion.

In my experience, it seems like if you have copper to galvanized steel contact anywhere on the copper pipe, the copper pipe will corrode where it is grounded.



I can not tell for sure, but the background of that picture looks damp in my opinion. Another pic of the floor joists behind it as well as the wall might reveal a moisture problem. Any vapor barrier in there?

No vapor barrier, but this crawlspace was about as dry as they come around here. I think they need a vapor barrier in this particular crawlspace to keep the soil from drying too much and shrinking/cracking. The soil was pulling away from some of the post footings and most of the interior posts were slightly loose.
I haven’t seen anything quite like it.

The galvanised strap/pipe support on the right is not correct. Needs to be copper or plastic to prevent galvanic corrosion.

As most of the corrosion looks to be on the top of the piping perhaps something is dripping on it.