Bending Radius of Steel Tube

http://cr4.globalspec.com/thread/41119/Steel-structure

Normally bending radius (CL) is 5xOD

With proper mandrel, you may be able to bring it down to 3xOD

With mandrel and hard packing inside about 2.5xOD.

It all depends upon the angle of bend, material of the tube, condition (CDS or seamless we have found are better adapted to short bends) and mandrel.

Try it out and then check the tube thinning and that is the critical portion.

Got a link which says 1D is also possible

http://www.advancedtubular.com/gendoc0001.html

But We have as on date been struggling with 2.5D (180 deg bend)

I was taught, many years ago, and still use it to this day...........4 x OD as the minimum bend diameter. Problems can occur with increased turbulence and erosion if minimum bend diameter is decreased..........in other words you reduce the life expectancy of the piping/elbow.

If the material is very ductile the outer wall will become thinner but it will still keep. The problem with smaller radii is the inner side where a series of waves can appear since there is an over elasticity limit loading and loss of stability.

If you want to use smaller radii it is compulsory to guide the tube and avoid its ovality using a saddle on the inner side.