During a tube bending process, a section of the tube becomes an outside part of a bend, also called an extrados, and another section directly opposite to it becomes an inside part of a bend, also called intrados. The original tube material in the outside bend gets elongated during this process and its thickness decreases based on the formula below. The original tube material in the inside section is compressed and its thickness increases.

t_ex = t * 2 * R / (2 * R + d)

t_ex - thickness of tube at extrados
t - original tube thickness
d - tube diameter
R - centerline bending radius