I often make hollow formed branches in various things i make such as table legs. In most cases I begin with either 12 or 14 gauge sheet about 4” wide and 3’ in length. I put on the bark texture then roll the sheet into tube. Most of the work results in limb-like stock less than three or four inches in diameter.
However, I sometimes start with pipe or tube when I’m making 1/2” to 1” diameter elements. I have made some dies to create the texture without creating excessive collapse deformity.
I begin with two mild steel blanks about 5/8” x 2” x 3”. I chose a round bar mandrel slight smaller that the tube to be textured. I position the two die block blanks to allow easy insertion of that mandrel and hold them in place with a couple of small pieces of welded flat bar scrap and add a porter bar handle.
The assembly is heated evenly to a high forging heat and placed in the hydraulic press. Usually one squeeze finishes the set if the heat was right.
The final step is to run several long MIG beads longitudinally. These are the ridges which do the texturing. The dies can then be joined is some facing to keep them reasonably well aligned. In this particular type of die the alignment is not really very critical.
Because the die working face is only a couple of inches in length the tube can be textured, tapered and bent all in a single process.
I’ll add some images of the dies later.