Bending Radius for steel Pipe

5 times the outside diameter is pretty common

It depends on the pressure drop allowed from a fluid perspective.

And from a code perspective it depends on material, thickness, type of bending performed (hot/cold), maximum fiber elongation, and ultimately any heat treatment required.

For reference please see Sec. 332 of ASME B31.3

If your pipe will operate to belonging to ASME B31.4 (liquid) or ASME B31.8 (gas), there mention allowable radius. From that value you can draw or calculate, to get allowable degree.

Thanks