Schedule 160 pipe

[tranc14]

When heating a 2" pipe that is 15' long in a furnace thats 1800f for about 3 minutes. If you were to bend the pipe in a spiral motion will the inner dimension lose its shape?

 

[gr2vessels]

Yes, the inner and outer dimensions also. It will "relocate" the neutral fibre in the pipe wall thickness and flatten the round shape proportionally to the stresses induced by deformation. I assume that you are using some sort of cylindrical template to generate the spiral, otherwise you'll end up collapsing the cross section somewhere, at a weaker point along the pipe.
Please note the heating will only reduce the resisting stress in the pipe material, to lower the forces required to deform the pipe. It will however, lower the cold work residual stresses.
Cheers,
gr2vessels