Deep-Well Problem?

Question

I installed a 5hp motor with a 27 GPM pump at 230 feet deep. I used 2 inch galvanized steel pipe. I had to pull the pump today and I discovered that the bottom 100 feet of the pipe (and pump) unthreaded at the couple and fell into the well at 136 feet. Why did it unthread from the couple? It was extremely tight upon installation and all involved are completely baffled.

Answer 1

That leads to a whole bunch of other questions. Mine is, does the pump starting torque tighten the pipe threads or loosening ?