The main water line is buried in a perimeter foundation on my hundred year old house. The threaded part that connected to all the plumbing inside and outside of the house broke off leaving the top of the pipe flush with the concrete. Can I thread the inside of this pipe and then screw in a smaller pipe to gain a way to reconnect without having to jack hammer the foundation to access enough of the pipe to thread the outside?
It may be possible but I would be concerned that the age and condition of the pipe might make it brittle and not good for tapping threads into.
My suggestion for a solution would be to rent a "core augur" and drill a new hole nearby through the foundation, and fix the pipe outside the structure. Run the new pipe through the new hole and abandon the old pipe.
I had the same issue in my 120 year old victorian home. The pipe broke because it was rusted through too thin. I agree with the previous answer: replace it with new plumbing. And do so every time you must plumb. It be better in the long run.