Propagation Buckling of Subsea Pipelines and Pipe-in-Pipe Systems

This chapter investigates buckle propagation of subsea single-walled pipeline and pipe-in-pipe (PIP) systems under hydrostatic pressure, using 2D analytical solutions, hyperbaric chamber tests and 3D FE analyses. Experimental results are presented using hyperbaric chamber tests, and are compared with a modified analytical solution and with numerical results using finite element analysis for single-walled pipelines and PIPs. The experimental investigation is conducted using commercial aluminum tubes with diameter-to-thickness ( D/t ) ratio in the range 20 – 48. The comparison indicates that the modified analytical expression presented in this work provides a more accurate lower bound estimate of the propagation buckling pressure of PIPs compared to the existing equations, especially for higher D o /t o ratios. A 3D FE model is developed and is validated against the experimental results of the propagation bucking. A parametric FE study is carried out and empirical expressions are provided for buckle propagation pressures of PIPs with ( D o /t o ) ratio in the range 15 – 25. Moreover, empirical expressions are proposed for the collapse pressure of the inner pipe ( P ci ), the proposed empirical equation for P ci , is shown to agree well with the experimental results of the tested PIPs.