Lateral Buckling Theory and Experimental Study on Pipe-in-Pipe Structure

Abstract

With the increasing depth of marine oil and gas exploitation, more requirements have been proposed on the structure of deep-sea oil pipelines. The influencing factors of lateral buckling of a pipe-in-pipe (PIP) structure containing initial imperfections and its critical force were investigated in this study by conducting an experiment, a finite element analysis, and a theoretical derivation. The change laws on the influence of initial imperfections of the PIP structure during thermal loading were revealed through an experimental study by using imperfection amplitude and wavelength as parameters. Appropriate finite element models were established, and the influences of initial imperfections, pipe-soil interaction, and the height and the number of centralizers on the global buckling critical force of the PIP structure were analyzed. The formulas of global buckling critical force of inner and outer pipes and that under pipe-soil interaction was obtained by using a theoretical derivation method. A comparative verification with experimental and finite element (FE) models result was conducted, which provided a corresponding basis for steel pipeline design.

Investigation of the Torsional Effects on the Lateral Buckling of a Pipe-Like Beam Resting on the Ground under Axial Compression

“…The equation system (19) will be solved below for two particular choices of boundary conditions: concerning the tranverse displacement, simply-supported conditions will be equally assumed in both cases (as already considered in many previous studies, such as [39,40]), whereas the torsional rotation at the ends of the beam will be either fixed or free. All the subsequent results are applicable, provided that the following condition is fulfilled (which is always the case in practice):…”

“…Considering now, for simplicity purposes, that the middle of the beam corresponds to the longitudinal coordinatex = 0, only even functions will be involved in the sought buckling modes. Hence, the general symmetric solution of the equation system (19) for the lateral displacement turns out to be in the following form:ū z = c 0 + c 1 cosh(ax) cos(bx) + c 2 sinh(ax) sin(bx)…”

“…Wang and van der Heijden [5] made use of a more realistic non-linear pipe-soil interaction model that accounts for the effect of lateral breakout resistance. The use of these pipe-seabed models depends on the type of seabed, which may consist in soft clay [17,13,18], stiff clay [16] or sand [19]. In practice, the pipe is supposed to penetrate into the seabed with a finite depth, giving rise to a finite contact area between the pipe bottom and the seabed.…”

“…The conventional design practice for the pipe-soil interaction assumes thus classically a uniform frictional behavior in the horizontal direction (proportional to the pipe effective weight underwater, in the simplest case) [27,23]. With these simplifications, spring elements shall be used to represent the resistance force in the pipe-soil interaction, assuming the seabed to be rigid [28,11,29,19].…”

Lateral Buckling of Pipe-in-Pipe Systems under Sleeper-Distributed Buoyancy—A Numerical Investigation

“…The third one is to stimulate controlled lateral buckling (vertical buckling is usually catastrophic) at the appropriate location [7]. Even with the increase in pipeline laying depth, most deep-sea pipelines can be directly laid on the rugged seabed, and the lateral buckling of high-temperature and -pressure pipelines is almost inevitable [8,9].…”