How large (torus tube dia, outside diameter of torus, total volume required, pressure required, wall thickness, "pipe" material, inlet/outlet, cross flow requirements)?
Fabrication COST (underline, bold, italics, red color to emphasize!) is the real key. It is extremely expensive to fabricate a very large high pressure torus by rolling the individual plates: Not impossible, but more expensive than a sphere. Least expensive pressure head is the "standard" flanged and dished for that reason. Even half-spheres are expensive compared to the F&D. Now, if you can get by with buying 4x simple 90 degree butt-weld short radius pipe elbows ....
Also: How are you going to get in and out: Most "ideal" torus designs don't include the large manway and piping welds that add to expense and reduce theoretical wall strength at each complex joint. Again, not impossible, but you need to figure that reinforcement at EVERY non-optimum positions.
Also: If your intention is to create an ideal torus get as high a pressure as possible with as little metal as possible (low wall thickness) you now have much more "wall" area on the torus than a sphere.
