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Although P-delta effects can have a significant effect on some plant piping layouts, P-Delta analysis with large displacements can be particularly important in analysis of buried and seabed pipelines where soil friction causes built-up compression forces that can make lateral or upheaval buckling a design concern. In the widely referenced paper, “About upheaval and lateral buckling of embedded pipelines”, author Dr. K. Peters emphasizes that rigorous analysis of upheaval and lateral buckling requires “second order solutions” (aka P-delta analysis), and he warns that “piping programs not able to produce second order solutions may not be used in solving upheaval or lateral buckling problems."
In addition to more realistic analysis of compressive forces in pipelines which are not perfectly straightPiping ball joints, flexible hoses, and swivel arms can also involve large displacements which need to be properly accounted for.
In addition, P-delta with large displacements enables engineers to more accurately calculate stresses and reactions in layouts where flexible piping exhibits catenary behavior. Following is a simple example illustrating the effects of P-delta with large displacements which users can easily reproduce with their own piping stress program. Pipe section OD 6.625" wall thickness .188", A106-B, fluid contents specific gravity 1.0 (water), no insulation. 80 ft. span of unsupported pipeline divided into 5 ft. segments. Anchors on each end have moment releases with rigid fixity in all 3 translational directions. That is, anchors are rigid in global X, Y, and Z direction with no rotational restraint stiffness.
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You can create this example with your own piping stress program and compare with CSiPlant by downloading a free fully-functional CSiPlant trial license by clicking the "Trial" link here https://www.csiamerica.com/products/csiplant
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We welcome users of other piping stress software to compare their results with results from CSiPlant. If your piping stress program is incapable of properly considering second order P-delta resultseffects, then results may not be realistic in some (many?) designs, particularly with analysis of buried and subsea pipelines.
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