Pipe wall thickness reduction during bending

[Mechh007]

3/4"Sch 80 and 1" Schh 80 pipes bending radius is 5D. How to calculate the wall thickness of these pipes after bending? What will be thinning after bending. Please find the attached drawing for your information.

 

[bernoullies123]

The bending operation stretches the outer portion of the bend (extrados) and compresses the inner portion (intrados). This results in thinning of the extrados and thickening of the intrados. Due to uncertainties in the pipe bending method/operation and pipe wall thickness tolerances the exact thinning cannot be determined. An approximate value can be determined by the follow ratio:

R / (R + r)
where: R is the radius of the bend; r is the radius of the pipe

(Ref: Piping Handbook 7th ed., by Mohindar L. Nayyar equation A6.1)

 

[davefitz]

for the small pipe , it should be easy to simply buy some extra pipe and perform the bend test yourself and use a UT device to survey the wall thcikness before + after, using exactly the same process you expect to use in the final contract.

The concern regarding loss of wall thickness at the extrados is normally countered by the 2 arguments (a) using the toroidal equations for stress in a torus , the extrados is stronger thus needs less wall thickness and (b) cold work harrdening of the extrados makes it stronger.

Check your design Code if such arguments are permitted.

 

[Mechh007]

Bernaullies,
R - bend radius,5D
r - ? Pipe outer radius or inner radius ?

 

[bernoullies123]

sorry,

r = the radius of the pipe (1/2 the outside diameter)