I am trying to replace a stuck gate valve that does not close,
probably due to hard water. From the gate valve are pipes
that runs three feet in both direction from the well pumping
tank and into the concrete floor. Someone had connected the
gate valve onto the pipe before setting the concrete. In order
to remove the valve I would have to twist a pipe. Their seems
to be no way to twist the pipes. What's a practical way to
remove the gate valve and install a ball valve in in cases
like this?

Thanks