Critical force of upheaval buckling for imperfect subsea pipe-in-pipe pipelines on nonlinear foundation

Upheaval buckling behaviors of imperfect subsea PIP (pipe-in-pipe) pipelines on nonlinear foundation are studied using finite element method. A parametric study is performed and the effects of the parameters on the critical force of upheaval buckling are discussed, including initial imperfection amplitude to wavelength ratio (AWR), the characteristic parameter of initial imperfection shape, stiffness ratio, clearance between outer and inner pipes, and soil condition as well as vertical pipe-soil interaction. A simplified empirical formula considering the above factors is presented to determine the critical force of upheaval buckling for subsea PIP pipelines based on dimensional analysis and the results of the parametric study. The results of case studies show that the proposed empirical formula has good accuracy.