CSiPlant offers P-Delta analysis, including P-Delta with large displacements. P-Delta analysis, also known as second-order geometric nonlinearity, involves the equilibrium and compatibility relationships of a structural system loaded about its deflected configuration. It also accounts for real world changes to element stiffness due to axial loads, as tension loads increase lateral stiffness of elements, while compression loads reduce lateral stiffness. The tightening of guitar strings is a good example of the effects of P-delta effects changing element stiffness. These changes in element stiffness affect piping and frame resistances to lateral loads.
P-Delta analysis has been a near-mandatory requirement in structural design codes for many years due to the importance of its effects in design calculations. However, piping stress models have traditionally ignored P-Delta effects, possibly because most older generation piping stress software programs are incapable of P-Delta analysis.
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."
FRP/GRP piping and jacketed pipes are are also susceptible to buckling from compression load build-up due to axial friction. Piping ball joints, flexible hoses, and swivel joints can also involve large displacements which need to be properly accounted for in design calculations.
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We welcome users of other piping stress software to compare results from their results with program to results from CSiPlant. If your piping stress program is incapable of properly considering second order P-delta effects, then results may not be realistic in some (many?) designs, particularly with analysis of buried and subsea pipelines and other applications mentioned above.