Fix the pipe, insert the pipe with a steel plate slightly wider than the inner diameter of the pipe (the width of the steel plate depends on the elasticity of the pipe, and the pipe can bounce back to the diameter after pulling out the steel plate), drip lubricating oil, and twist it several times in the steel pipe with a wrench.

You can also use a steel plate as a fixture outside the pipe, drop lubricating oil and screw it outside; If there is a suitable big wrench, the opening is slightly smaller than the outside diameter, and it can also be used as a fixture.

You can also squeeze the large diameter side into the vise, but you are afraid of hard folding.