axial buckling
axial buckling
(OP)
What are the criteria to evaluate the buckling effect for underground piping?
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RE: axial buckling
Allowable axial loads for tubular structures are available in tank codes, AISC-ASD, perhaps ASME B&PV, and a number of other sources, if your design code doesn't specify anything.
If you have significant earth loads, that will reduce the allowable axial load.
RE: axial buckling
RE: axial buckling
No special requirements for buckling there but the customer want a axial buckling evaluation.
RE: axial buckling
RE: axial buckling
Use Section VIII Div 1 rules for cylinders under axial compression or Code Case 2286.
RE: axial buckling
RE: axial buckling
Note that for small-diameter pipe, application of the local buckling criteria will just show that the pipe can yield before it buckles. And if it's large enough and thin enough for that not to be the case, then earth loading is liable to be more significant.
RE: axial buckling
The operating temperature is around 300F. I have large deflections and possibly large axial forces. The pipeline is restrained axially by friction and sometimes by natural or real anchors.
If the axial forces are high the pipe can buckle. The soil will act against the movement and it will reduce the vertical and/or lateral movement.
In what circumstances the vertical and/or lateral buckling can occur? How can I calculate the maximum axial force to prevent the buckling considering the elastic-plastic behavior of the soil?
RE: axial buckling
You might check with people familiar with piling. Piles are normally designed assuming they have lateral support from surrounding soil, not as free-standing columns, and I suppose similar issues arise there.
RE: axial buckling
This source will should answer your questions:
http://www.americanlifelinesalliance.org/pdf/ASCE_...
RE: axial buckling
I found calculation for side wall crushing, and ring buckling. Nothing about axial buckling for buried pipe.
RE: axial buckling
RE: axial buckling
If you want to do a calculation for column buckling, you can run a FEA with a long beam with periodic spring restraints representing the soil stiffness. Look to the B31.1 appendix VII for a method to calculate effective springs that simulate soil stiffness. But you should learn from this exercise that there is no problem with Euler buckling of buried pipe.
Of course there are local effects such as wrinkling due to bending a pipe over a change in direction, buckling due to soil loads under some circumstance, buckling due to external pressure (e.g. pipe under the water table), etc., but my understanding is that the question is with respect to axial loads.
RE: axial buckling
I know the soil characteristics and the spring rate for interaction with the pipe.
The level of stresses is under allowable but the axial buckling happened and the pipe popped out from the ground. I guess that the cause is axial buckling
There is not limitation for axial force in B31.8.
RE: axial buckling
What is more likely is that you had a vertical change in direction, so it is the thermal expansion forces pushing on that change in direction that pushed the pipe out of the ground. Folks use intermediate anchors at such changes in direction to handle that effect.
RE: axial buckling
But I still need to prove that Euler buckling did not happened.
RE: axial buckling
Look at B31.1 Appendix VII to figure where the virtual anchors are, and how much the pipe would actually move should it be able to.
See if all this explains what was observed.
Note that if the pipe is perfectly straight, it takes negligable lateral restrain to prevent axial buckling.
RE: axial buckling
A lot of work has been done on this, especially in the late 80s. For example SPE 68224 concerns a HP/HT gas line in Abu Dhabi, where section of the line started to protude from the trench soon after operations started; there are lots of OTC papers: OTC 6846 "Soil response for upheaval buckling analysis, full scale lab tests", OTC6333 "FEA model for analysing upheaval buckling response of submarine pipelines", OTC 6335 "Design of submarine pipelines against upheaval buckling", OTC 6488 "Upheaval buckling failures of insulated buried pipelines: a case history" etc etc.