Another point of interest is that steel pipes are not all round and the same diameter over their full length.
They looked perfect until you put them in a lathe.
Wrap them in carbon and with a little shrinkage as the resin cures and small differences can become a real problem.
I have recently had the need for perfectly round and true pipes. I had to turn them down on my lathe to get them that way.
I would really like to find out the dia of the tube that you are trying to make. Collapsible mandrels are easy to make for larger dia tubes.