Again, what's the actual spec of the tube? Bright annealed bends more cleanly than as drawn/welded and descaled.
Remember that i'm basing this on the Pearson version/colours of this type of press bender... i'm pretty sure that the wall thickness is just too thin. As i said needs to be 14swg/2.00mm for stainless above 2" OD.
Which bender and what dies are you using?
Al
worth a look here
http://toolsforbending.com/
and having a look in the literature section at the tube bending manual. Theres lots of good troubleshooting advice in it.
Dunno if you bought this new or used or have a manual etc but the manual is available from the Bendpak site... http://www.bendpak.com/Pipe-Bender-Manual-REVA.pdf. I've only scanned through the thing but there's a trouble shooting section near the end with pics of mangled bends and the usual causes- it may not be as comprehensive as the other trouble shooting links posted but is probably more applicable to your kit as the others are more specific to rotary draw bending while yours is a press bender. There's a section on bending stainless tube including recommended back pressures (2400-2700psi for 2-2.5" OD). The bit on stainless tubing spec is a bit lacking to say the least... if you're working with 304/316 stainless then just ask for annealed tube. While the manual says it'll bend 16swg wall upto 2.5" dia at the start note that at the start of the bending problems/trouble shooting section it lists 14swg/2mm as the min wall thickness for 2.5" OD