(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."
Cold bendings set limitations on minimum bend radius (piggability/fibre elongation-18D for NPS 6 per ASME B31.4 in your case), minimum wall thickness (shouldn’t be lesser than 87.5% of the pipe wall thickness) and ovality (8% in ASME 31.3). If welded pipe, longitudinal seam should be as close as possible to the neutral-axis.
Check what construction code you follow and go from there.