When Copper Pipes Go Bad

This is a section of 3/4" copper supply tubing I removed and replaced from under my house today after it developed a leak. I've never seen pitting on the outside like this before.

Also notice the red coloration within the pitted area. Anybody have a clue what is going on here?

It's an old house but the copper appears to be fairly new. There is no noticeable corrosion or build-up on the interior of the tubing.

Bill is the owner and maintainer of SoftPlanTuts.com