Upheaval Buckling of Buried Pipeline 1

[Johnrem]

Dear Specialist;

I’m facing a problem of upheaval buckling of a gas injection buried pipeline. Originally the pipeline was buried 1meter below the ground (01 meter from ground to the top of the 10” pipeline).
As you can see in the attached photo, due to thermal expansion, the pipeline is coming out from its trench. I’m requested to provide a solution but I have no idea how to proceed.
1) Please help by giving your advices.
2) As you know, we used to provide expansion loops in order to absorb a thermal expansion of above ground pipes.
If we provide an underground loop for an underground pipeline, can someone tell me if it will absorb thermal expansion or soil lateral bearing effect will not allow. In other words, is it usual to provide underground loops for buried pipes?

Thanks in advance

 

[athomas236]

Eyeoftheneedle,

What are your thoughts on the latest posts.

Regards,

athomas236

 

[BigInch]

Where you use overbends and underbends in the pipeline to conform to the land's elevation profile, essentially you already have the shape of a buckle, but maybe its not visible. In these cases you assume you have an arch structure, fixed at both ends, at the virtual anchor distance, or at underbend inflection points. Calculate deflections with pressure and temperature expansion, weight of pipe, contents and soil and simply put enough soil load (burial depth) at the overbends to hold the deflections neutral.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[Johnrem]

More explanation and advices, please.

 

[BigInch]

Most of the upheaval calculations are directed towards predicting the risk of its occurance and then the possible shape of the deflection. When following the ups and downs of the landscape, you know the shape because the pipe is bent into that shape when its laid down in the trench.

When crossing the top of a hill for example, you have two valley points on each side and, if uplift occured going over the top of the hill, it is likely that the valley points would not be forced further down, but in fact form rigid supports for what would become an arched segment of pipe crossing over the top of the hill. You then have a structural problem of analyzing an arch composed of a pipe section with weight of pipe, contents, insulation and soil on top. As the pipe expands longitudinally due to temperature increase, the overbend portion would be forced up and out of the trench. It then becomes a problem of "simply" burying the pipe enough so that the soil weight on top of the pipe will hold the pipe down in the trench rather than allow the pipe to expand and be forced out of the trench at the top of the hill, while still not allowing it to become overstressed at any point. Maybe the attched diagram is more clearly describing the effects you need to consider. You know the as laid shape of the arch which can be analyzed for deflection and stress by structural mechanics for distributed load, with a superimposed thermal expansion.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[Johnrem]

Big thanks for you BigInch;

I got your explannations. However still can't understand followings:
1) When crossing hills or dunes, is there any requirement regarding the trench profile? I think we can't cross hills and dunes just by laying down the pipeline in the trench. I think we have to smooth the crest of the hill(or dune) and provide a radius equivalent to elastic bend (around 500 time O.D) for it. Vertcal field cold bends are generally rejected by Clients, that's why we shall use elastic bends.

2) If you have experience with Palmer calculation, please inform what shall be 'di' (imperfection depth) in my case?
As it is shown on my previous attachment, the difference of elevation between the crest of the hill and the vally is around 15m (49 feets). Can'I consider these 49 feets for 'di' ?

Best Regards

 

[BigInch]

Elastic bending, natural sag, or natural end deflection is preferred for vertical curves, its cheaper to let gravity do the work, but technically there is little difference in a vertical cold bend, or a horizontal cold bend.

Don't use the equation. I assume its going to happen when you have a certain bend angle and specify burial depth to control it.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[racookpe1978]

Have you been able to verify that the light-weight sand at the top of the dune hasn't been blown away from the pipe?

It's a very, very small cover (1 meter total) obviously using the locally available wind-blown sand crystals right next to the ipe.

If the dune blew away, the pipe is uncovered (and supported in both adjacent "valleys" as mentioned by BigInch. So the rigid or stiff coverings of a dirt and gravel (US typical) fill over a pipe simply are not present.

You need to face the problem of needing to check both valleys. If coverage is correct in both valleys (and who's to say that the pipe was really buried 1 meter deep as it crossed the original dune contour???) then you need to "shorten" the pipe to lower the hill (the visible bump in the pipe) back into the new dune contour minus the 1 meter pipe cover now missing. This will require removing 2-4 meters of pipe and obviously, re-digging the ditch, then re-welding the pipe inside the new ditch. IF (big IF!!!) the new dune height is stable: if the new dune contour blows away again, then you are back to today's picture.

To keep the pipe the same length, you need to dig an s-shaped curved ditch the right length to make up the total length of the bow, plus the new ditch depth.