Buckle propagation in pipe-in-pipe systems.

Abstract

Abstract In Part II we examine and evaluate the performance of three levels of models for estimating the two new propagation pressures of pipe-in-pipe systems introduced in Part I (PP2 and PPS). The first type of model involves uniform collapse of the system through a kinematically admissible mechanism resulting from the formation of plastic hinges. Closed-form expressions for PP2 and PPS are derived which provide a valuable qualitative view on how they depend on the main parameters of the problem. The predictions, however, significantly underpredict the measured values. The second type of model also involves uniform collapse but is conducted numerically instead. An energy balance between prebuckling and collapsed configurations obtained from a uniform collapse model yields approximate values of PP2 and PPS. It is demonstrated that such predictions are within acceptable engineering accuracy. The third type of model involves fully three-dimensional numerical simulation of the initiation and steady-state propagation of collapse. It is demonstrated that, provided the geometric and material characteristics of the pipes used are accurately represented in such models, both PP2 and PPS can be predicted to great accuracy. Such models are, however, numerically intensive. Part II finishes with conclusions and design recommendations drawn from both the experimental and analytical parts of the study.