Torque required to bend pipe??

[PistonRod]

What is the equation for the torque required to bend sch 160 steel pipe 90 deg with an 18" inside radius using a rolling style bender?

Is there a generic equation for this?

 

[JStephen]

You could approximate the bending moment required to bend the tube by assuming the yield stress or perhaps 1.2 times the yield stress over the whole area. IE, "plastic hinge". Depending on the geometry of the machine, it might be easiest to work with the energy required for deformation.