Collapse mechanisms of pipe-in-pipe systems under external pressure during operation

This study investigates collapse mechanisms of the inner pipe of a pipe-in-pipe (PIP) system under external hydrostatic pressure. It is observed that the geometric and material properties of the outer pipe affect the collapse pressure of the inner pipe (Pci). A finite element analysis (FEA) is presented and is validated against the experimental results. Using the validated FEA, a parametric study is conducted. An empirical expression is proposed for Pci. Then the collapse mechanisms of the inner pipe during the operation, by incorporating various fractions of the burst pressure in the inner pipe, are studied using the FEA and are compared to the response of PIP with no internal pressure. It was shown that the collapse pressure of the inner pipe when the outer pipe caused a local contact pressure is not significantly affected by the internal pressure. © 2019 by the International Society of Offshore and Polar Engineers (ISOPE).