On lateral buckling of subsea pipe-in-pipe systems

Lateral buckling is a common phenomenon in unburied high temperature and high pressure (HT/HP) subsea pipe-in-pipe systems. An effective finite element model based on beam element and tube-to-tube contact element is proposed to study lateral buckling in pipe-in-pipe systems, in which the initial imperfection (out-of-straightness), nonlinear pipe-soil interaction and nonlinear material properties are considered. The results show that it is the resultant axil force of the inner and outer pipe that governs the lateral buckling phenomenon in pipe-in-pipe systems. The initial imperfection and pipe-soil interaction are the most important factors which influence evolution of the displacement and stress in pipe-in-pipe systems. Nonlinear material properties are necessary when plastic strain may occur in post-buckling stage. At last, a simplified model is proposed which can easily calculate the critical buckling temperature of the corresponding pipe-in-pipe system.