I have a suggestion for you. Being in the same situation, I would recommend you contact Welding Services, Inc out of Atlanta, GA. They can help you either directly or indirectly.
Most in place machining contractors have boat sample cutters, i.e.: PCI, MTI. Thielsh Eng does also. Make sure the operator is experienced using it, or the boat sample repair may be worse than the original failure mechanism. Also don't try to mount the cutter on the pipe diagonally. If you need a boat sample diagonal to the axis of the pipe, take it out with a grinder, wafer wheel, and a competent craftsman.
We ended up making our own station air driven unit about ten years ago after failing to find one on the market for lease or purchase. I'd be interested if you end up finding one.
the contractor had a contact that had one and they shipped it to the site.
it was interesting watching the process, considering the sample material was at 400deg F and the technician had to mount a 100lb mini-machine to the material - ouch!
