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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. In fact, ASCE 7 has over 100 mentions of P-delta (P-Δ). However, piping stress models have traditionally ignored P-Delta effects since most older generation piping stress software programs are incapable of P-Delta analysis.
As this Ansys article says regarding large deflection (aka P-delta): “geometric nonlinearity involves a few different concepts and it is not always easy to identify when it is required.” and “If you don’t know if you need large deflection (P-delta) or not, you should turn it on. There is really no way to know for certain if it’s needed or not unless you perform a comparison study with and without it.”
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."
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