Cold bending pipe

[lambbalex]

Hello all,

I have been given a task to calculate the maximum allowable bending angle for pipe. This goes for pipe size from 0.405" to 48.0" in O.D. I was wondering if anyone can lead my in the right direction for this project, thanks!

 

[LittleInch]

Well depending on what your bend radius is and any other limitations you want to impose, it's anywhere from 1 to 90 degrees.

You're not really giving us much here...

Pipe design code you're working to, max bending radius / strain value, bend thinning allowance, type of bending, length of pipe, length of straight tangents etc etc.

Pipe SMYS, thickness all come into it.

I've successfully cold bent 6" & 8" pipe to 10D but it was a big effort. Most pipelines operate 40D as "cold" bends which equates to less than 2% strain and falls under the limit of 403.3.3 in ASME B31.4 for maximum strain. You can bend to t tigher radius depending on diameter but most people seem to stick to 40D.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Bend angle depends mostly on wall thickness getting thinner with increase of curvature. Wall thickness you need depends on the required pressure capacity. Too much curvature can cause local wall buckling.

A general rule of thumb for cold bending that works almost all the time and that is easy to remember is to limit curvature to 1 degree from tangent per length equal to 1 diameter of pipe. That is an equivalent of 60D.
40D will work for most pipe, but check your wall thickness reduction with bending and that need for the required pressure, especially when using sch10 or less walls.

Circumference of a 360 degree bend = C
C = pi * D = = 360deg * D_pipe
C = pi 2R = 360deg * D_pipe
R = D_pipe * 360/2/pi
R = 180/pi * D_pipe
R = 57 D_Pipe round that up to 60D

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[EdStainless]

For small diameter this gets a little more problematic as roundness becomes a major issue. We found that for sizes under 2", with walls that were at least 6.5% of the OD, using matched OD tooling (support all around OD, clamped both sides and fed onto a formed bend die) we could bend R=10d and keep thinning and ovality less than 10%.
If you bent with just and inside form bender then R>30d was required.
If the bend was made with a flat tool or no tool then R>50d was needed.
Sch10 was no real problem, sch5 got dicey. (we made tube as light as 1.125" OD x 0.018" wall)

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P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

An ancient guideline exists that addresses your question.

Pipe bending, PFI Standard ES-24, Pipe Bending Method, Tolerances, Process and Material Requirements, may be used as a guide.

Be aware that newbies cold bending of piping can generate a lot of very expensive scrap... Some wall thinning and ovality cannot be repaired

Some diameters/wall thicknesses and materials will ovalize when bent

Cold bent pipe MUST BE DONE IN ACCORDANCE WITH YOUR CODE OF RECORD. Different codes have different limits on wall thinning acceptability.

MJCronin
Sr. Process Engineer