Guide or calculations to bending Pipe of Pipelines

[juancd200914]

I am developing the Engineering for a 4 inch Schedule 160 Pipeline, in Standard B31.4 I have the table with the minimum radius to bend the pipe cold but I need to calculate the minimum bend radius as a function of the pipe has external coating and schedule 160 I appreciate your help

 

[LittleInch]

juan,

A 4" pipeline is rather small but I can't really understand your question.

The radius is based off OD of the pipe minus any coatings.

However Sch 160 is quite thick and cold bending is an art not a science.

Be sure that whatever radius you use is actually possible to get constructed / bent.

I've seen cold bends of 10D in my time but it took a LOT of effort not to wrinkle them.

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

 

[MikeHalloran]

I am not a pipeline person by any definition, but I have personally bent hydraulic tubing up to 2" OD.

To make a bend anywhere in the range of '10D', meaning centerline radius is ten times the pipe OD, you generally need some kind of tooling, comprising minimally a curved shoe that supports the inside radius and keeps the 'inner side' walls from ballooning out where the material is being compressed in cold bending, plus a hook of sorts to grab the stationary tangent, and a sliding shoe that moves around outside the shoe and forces the moving tangent to be, er, tangent to, the shoe while applying compression to the 'outer side' walls. Such a bender can be as simple as the 'conduit hickey' you find at Home Depot, up through 'compression benders' as awkwardly described above, to 'mandrel benders' that support the inside of the tube while the outside is being bent.

All of those tools will leave scars in a coating on the pipe OD, and they're big and expensive and heavy and require power, so they're normally used in a shop, and any coatings are applied after bending.

I get the impression you are not asking about shop bending, but field bending, e.g. establishing some minimum radius for the trench into which the pipe will be laid.

That is off the edge of my experience, but I would take a run at it as follows:

Take a guess at an arbitrary radius to which the pipe must conform (via three bulldozers and fabric straps for instance), and calculate the strain in the pipe's outer 'fiber' at that radius. First compare it to the yield strain for the pipe material. Then compare it with the allowed elongation of the coating. Or even try a test bend in the shop to see what the coating can take, if you can't get a usable number from the coating supplier.

Or take a look at photos of similar pipe being entrenched. The pipe, being flexible on a large scale, assumes an S sort of shape as it is being lowered. Take a guess at the radius in a vertical plane, and infer that you can safely bend it to the same radius in a horizontal plane. There's your trench radius.

Or restate your question with a little more detail, Juan. Thanks.


Mike Halloran
Pembroke Pines, FL, USA

 

[chicopee]

In my past engineering projects, I only worked on thin wall tubing that was to be bent in a hydraulic tube bender, however, in your case, the wall thickness being slightly over 1/2", I SUSPECT that you'll need to heat(red hot) in order to soften the section to be bent. I have seen corrugated furnaces made at the Lebanon, PA Cleaver Brooks facility which require red hot heating 1/2" thick wall pipe in order to make the corrugations.

 

[racookpe1978]

Well, you should not (generally) be bending that thick-walled a series of pipe. Look again at your design and try to find out WHY you are requiring the fabrication shop to be bending (hot or cold) when the standard short-radius and long-radius elbows are readily available. And much cheaper, much more likely to accurately follow your pipe trajectory.

You will still need NDE for the hot bending or cold bending. Very likely to have crimped or distorted intrados bend walls, or thinned extrados walls. (Pack with sand or a commercial filler to try to avoid crimping or kinking.) If hot bent, what will the red-hot/orange-hot bending temperature do to your previous metalurgy and crystal structure? What will it do to you coating? What will the rollers and clamps and skids (rubbing) do to your exterior coating?

You (in general) should not be trying to find out "how" to bend the pipe that is that thick, but "who can bend a pipe that thick?" (in your area) and "how much will it cost to bend a pipe that thick?" Be very careful, one shop "can bend" that pipe the way you want, but another might be able to only do shorter lengths or lengths with fewer multiple bends. Either may, or may not, bid for your project.

 

[MJCronin]

Straight out of the crypt ....

Some empirical pipe bending guidance and experience from "the ancient ones" ...... PFI-ES 24 !!

http://pfi-institute.org/products

MJCronin
Sr. Process Engineer