Gas pipeline deformation 2

[ONENGINEER]

There is a gas pipeline overpassing a canal having an approx. span of ~ 80'. The pipeline is bowed upwards. Would this relate to the internal operating gas pressure or due to external geotechnical and support reaction A pic is attached for a better visualization.

 

[Latexman]

Pic?

Good Luck,
Latexman

 

[TugboatEng]

If the pipe were perfectly free and unconstrained, internal pressure would tend to straighten the pipe (see a Bourdon tube in a pressure gauge). External forces or constraints cause the bow. These can be related to internal pressure, a pipe rigidly constrained on both ends has to move somewhere. This is the least likely culprit, though as the thermal displacements are already many times greater than the pressure displacements.

 

[LittleInch]

Almost certainly the design at that sort of span the same sa an arch bridge.

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

 

[ONENGINEER]

Thank you for your replies. The missing photo is attached. Any hints how to quantify the internal forces that caused the bowing.

 

[TugboatEng]

Your photo doesn't show anything beyond what you described. Why are you concerned about the bow to begin with? Have you estimated the strain to cause such a deflection? You might find it to be well within the limits of concern.

 

[ONENGINEER]

TugboatEng. Thank you for the hint. Also I would like to know how much force does the pipeline apply to the concrete walls where the pipeline is supported.

 

[1503-44]

Hard to see the extent of the bowing from that angle.
The pipe was installed with the upward bending arch.
Load at each end is at least 1/2 the weight of the pipe plus contents.
I would add some amount of pipe that is embedded in the soil at each end, something around a length of 2x the depth and include the weight of the soil on top of the pipe too.
The bending moment at each end I'd estimate as (W*L^2)/10 where L= 80 ft, W = uniform distributed load = weight of (pipe + contents)/foot.

If you can get an accurate measurement of the profile, you may be able to get better approximations of the pipe stress and loads.

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

 

[LittleInch]

It looks to me like this was a "cold" bend when the pipe was installed to make it meet the pipe on the other side.

The fact that the guide looks to be free tells me this is not a case of the pipe being forced into this shape. Self weight of the pipe is the key force. Very hard to give any forces without knowing the start point and orientation of the rest of the pipe.

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

 

[1503-44]

I'm not thinking cold bend, probably fab of a 100 ft span, lifted from two points near mid span, swung into position, held in place and welded in as an elastic bend. Of course just my guess.

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

 

[LittleInch]

From one poorly taken photo you can tell nothing.

25m of steel pipe is pretty rigid.

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

 

[HTURKAK]

The picture is not enough to get the full story.. My initial opinion is, the PL is buried at both sides of the channel and upward bowing is at open channel crossing portion.. The pl is not touching to the wall support and probably exerting uplift force with U bolts ..

My opinion is due to temperature..













Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[ONENGINEER]

Appreciate valuable feedback especially on static calculations, attaching another photo. Also how to quantify the potential bow due to internal pipe pressures (Bourdon?), if the bow was not based on prefab, thermal or installation condition. Can the internal forces be so high to force the steel pipe to bend and rupture the support bolts?

 

[3DDave]

Bourdon tubes are deformed to specifically amplify the change in shape due to internal pressure. The main deformation is diameter.

That pipe is bent because the installation is forcing a bend in it. It would look the same without any pressure at all.

 

[TugboatEng]

It's only meant to be a visualization. I did follow up by saying that the changes in dimensions due to pressure are insignificant relative to temperature and external forces.

 

[LittleInch]

The second photo doesn't really show any significant bowing.

It's not clear how long the lever arm is between the pivot point on the concrete wall and the point where the next support or burial point is.

It definitely looks to me like there is a cold bend at the concrete wall or just after to change the angle from either side to virtually horizontal across the canal.

Whatever is or is not causing any further bending, internal pressure has very little to do with it. External forces or movement or collapse of supports and /or thermal expansion are far more important in any bending of a pipeline.

Wind, snow etc also exert forces which can snap support bolts and create movement.



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

 

[ONENGINEER]

I got the points that I was looking for. Thank you all for the comments, each being enlightening.