Pipe Bending and Elongation

That's not a bend. That's a kink waiting to happen.

Why not use an elbow fitting?

Try filling the pipe with sand before you bend it. That may prevent the kink.

Still I dont think you can avoid it - almost D=r

some articles just for reference from my ref catalogue (not much pertinent)

http://www.outokumpu.com/pages/Page____19263.aspx

(copper tubes)

http://www.summo.com/tube.pdf

http://www.bendtooling.com/bending_formulas.htm

However in our use we have rarely bent at a radius 2Φ and usually it is at 2.5Φ.

Even at 2Φ it was not only difficult to avoid the kink (even with wiper) but also the thinning was excessive.

So nobody can show how to calculate fiber elongation?

See this link for bend allowance info:

http://www.sheetmetalguy.com/bend-allowance.htm

The problem you will have is that the wall of the pipe on the outside of the radius will strech significantly more than the wall on the inside. Hence the kink mentioned above.

Some guest already answered the calculation of pipe elongation based on
ASME.

Pls note that there are limitation of maximum elongation as per materials.

Your question did not mentioned any thing about the material. It looks like
that your hope will definately exceed the maximum elongation limit whatever
the pipe material is.

Some recommends filling sand before bending. Some does heating with torch.

However, I do not expect you to be able to avoid kink with such configuation.
If it is really necessary, it is better to have short radius fittings.

Bend inner radius by thumb rule is to be minimum 3.5 to 4 times the dia of the tube, based on the material and the hardness levels. Elongation will also vary per these varying parameters from 1 to 3%

Sorry I was not logged in to cr4....You have not mentioned the material and minimum length of bend you require. Bend inner radius by thumb rule is to be minimum 3.5 to 4 times the dia of the tube, based on the material and the hardness levels. Elongation will also vary per these varying parameters from 1 to 3%. Softer (annealed) the material, lesser the kink.

Radius that is lower than the above rule can be done with using low melting lead alloy that contains bismut and tin, as a filler material. In general this alloy is used in investment castings..can melt at boiling water.

Tube to be annealed and this alloy material to be poured after heating. you can acheive better quality bends compare to any other methods like sand, mandrel...Remove the filler material by heating the tube to 100 degrees or by dipping into boiling water. Bend annealed tube for better results and followed by hardening/age hardening to regain better mechanical strength. Bending to be done with a proper tool that will have wiper. Use lubrication while bending.

I have done ss and al tube bendings to aerospace/cryogenic application that has inner radius 1.6 times the OD with satisfactory burst test results. Elongation was 1.5% max.

You can try to your application and please keep me informed on results. If you can not bare this cost, best go for bend fittings from swagelok and weld/braze it. goodluck!