BulletProof, yes you are right, there is a possibility to create one NURBS surface for tube. I'm taking another approach. This is the same trick that I use for poly tube.

1. create a torus (8 section, 6 span) cubic type.

2. rebuild the surface (using keep CVs, U linear and V cubic.

3. delete isoparms u[1], u[4] and u[7].

You will then get a NURBS tube.

In polygon you have ability to twist the ring 45, so you can use only 4 spans and result directly as polygonal tube.