Minimum Radius of Pipe or Tube Bending

In Bending a pipe or Tube Outer Part of bend is Stretched and Inner part is compressed Due to this stresses pipe or tube can be flatten or Collapse.

To avoid flatten and collapsing Pipe or Tube minimum radius of bending to be equal 3.5 to 4 times diameter for standard pipe  and 2.5 to 4 diameter for Extra Heavy pipe.

so while bending of Tube or Pipe we have to keep in mind minimum radius.