Automation pays back fastest where you weld circumferentially and repeatedly: pipes, tanks, flanges, frames. You size a positioner for the mass of the part and for its overhang from the table. Watch the moment: a positioner rated at 300 kg will in practice lift far less with the part standing 300 mm off the table. Makers publish a moment chart, we give the load capacity and the maximum eccentricity.
The speed range decides your travel speed. For circumferential welds you need smooth adjustment across roughly 0.1 to 5 revolutions per minute and a speed that stays steady under load. A separate fast mode for setting the part up is useful.
Turning rolls are chosen for the diameter and mass of the tank. Check the diameter range and the roller material. Polyurethane does not mark stainless surfaces, steel lasts longer but leaves traces. One set is usually a driven unit plus an idler.
Welding tractors for fillet and butt welds over long runs give repeatable penetration. Look at how they are guided: rollers running along the plate, magnetic guidance, or a track. On thin sheet a track is the safer option.
In every case the way the welding current is returned matters. A poor contact burns bearings and gearboxes. In the product listing we give the state of the brushes or the slip ring and the measured resistance of the return circuit.
Before you buy, check whether your power source has an output for synchronising start and stop with the positioner. Without it automation still works, but the start and the crater have to be run by hand. In the listing we state what signals the controller carries and whether a remote or a foot pedal is included.