You should use the next diameter of tube to get easy conformation the the shape of the tube you are repairing. But, if you have no choice but  to use a patch from the same diameter tube, there is no problem with heating the patch to make it plastic enough to conform to the outside contour of the tube being repaired. If it doesn't lay down smoothly you can tack welt the patch where it makes contact with the tube, then heat the patch with the torch and gently tap it into place, till it lies down tightly with the tube, with a small hammer. You can tap and tack as you go until the patch is a tight fit, the weld it.

If you want to make a slip over repair using a whole piece of tube, you will have to use the next diameter tube as it would be virtually impossible to expand the diameter of a tube uniformly and continuously around its circumference.

Michael Horowitz wrote: I'm working with 4130.
I have a piece of tubing with a  series of rust holes which do not
cover an area greater than 1/2 ", so it appears a welded patch repair
would be appropriate.
Reading 43.13,, Figure 4-36, it appears the patch tube will have to be
expanded in diameter in order to fit over the injured tube (can't slip
the patch over the injured tubefrom an end).
Will there be any problem if I  heat the patch so I can open open it
and slip it over the injured tubing? - Mike