Field cold bend

[frank2121]

Hello friends,

I want to know your advice and opinions if the vertical cold bend pipe is mandatory to makes it During pipeline construction projects located in desert area.
It's possible to adjust the difference level of land by changing the depth of Trench excavation instead to make vertical cold bend?
Thanks

 

[LittleInch]

There's nothing "mandatory" about this. That implies it would be against the law...

A cold bend is normally 40D radius. An elastic bend which follows the ground without spanning or lifting off is normally about 600D.

So do a survey and find out if it works.

But more excavation costs more money so it all depends on how much excavation you need vs the small cost of a cold bend

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

 

[1503-44]

Small elevation differences can be accommodated by using natural curvature resulting from the flexibility of the pipe. It is not ideal, because it results in bending stress that remain in the pipe after it is buried. Those permanent bending stresses may reduce the amount of allowable pressure stress and the resulting allowable operating pressure. Natural bends must be limited to avoid overstress. That may require extra attention in areas where pressure stresses are high, as near pump stations or at low points in the pipeline. Combined stresses must remain below the combined stress allowed by your design code.

While a hot or cold bend is stressed above the yield point when being fabricated, when the forces needed to bend the pipe during fabrication are removed, bending stress are returned to zero. Having zero bending stress leaves the full strength of the pipe available for pressure.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[frank2121]

Thank you for replying.
About natural bend allowed, what is the maximum angle permitted for pipeline 20 inch.

 

[LittleInch]

No limit, but in practice rarely more than 5 to 10 degrees.

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

 

[frank2121]

Of I understand you, I can replace vertical bend 5 degrees by natural bend???

 

[LittleInch]

Yes, but the distance needed will be much longer than a cold bend.

All depends on what your ground profile looks like.

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

 

[1503-44]

You're not going be doing much natural sag bending of a 20" pipe.
That's for 2-4" pipe.
Do you know how little a 20" pipe flexes under its own weight?
Rotation of a pipe, beam supported at each end, is 5 WL^3/24/E/I =0.3 degrees per 20ft length
You won't notice it. You'll need 30ft of pipe to make one degree of change.

And check your construction specs. The practice is banned by many clients.

On the other hand you can cold bend to around 1 degree for each diameter of length.
For a 20ft long 20" diameter pipe, that's about 12 degrees. Since most natural earth profiles are less than 12 degrees and can be done with one joint of pipe.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[alchemon]

Physically possible - yes of course.

A good idea, probably not - on a 20".

But not my line...

Have you considered changing the grade if bending with a mandrel is not feasible?