ASME B31.4 and .8 both quote as follows
(b) Except as permitted under para. 406.2.l(c), the
minimum radius of field cold bends shall be as follows:
Minimum Permissible Bend Radius
Nominal Pipe Size : Bend in pipe Diameters
NPS 12 and smaller: 18D
14 : 21
16 : 24
18 : 27
NPS 20 and larger : 30
Bend R = 18D x 6.75" = 121.5"
Bend D = 2 x 121.5 = 243"
Bend Circumference 3.14 x 243" = 763" = 63.6 ft
Bend in Degrees per linear ft of pipe = 360°/63.6 ft = 5.7°/ft length
With 18D radius you can make a 50° Bend in a NPS 6 within a pipe length of around 10ft.
--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."