TEMA (Tubular Exchanger Manufaturers Assn) has something similiar. It is based on the simple geometry of the situation. That is, the wall thinning is inversely related to bend radius.
t0 = t1(1+do/4R)
t0 = original wall thk
t1 = "minimum required" wall thk
do = OD
R = centerline bend rad.
You can solve this for t1 and "predict" the final thickness based on OD, R and t0.
You may be able to use this, it depends on whether you are working to some Code or standard, or whether you need a great deal of accuracy (if so, I wouldn't!).
Hope this is useful.