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.
Highlights
With the gradual increase of marine oil and gas exploitation depth, high temperature, high pressure, corrosion effect, and ocean currents are all extreme conditions experienced by subsea pipelines, which result in enormous economic losses and catastrophic and irreversible environmental pollution [1]
Based on the experimental and finite element (FE) parameter analysis, we find that the initial imperfections, pipe-soil interaction, and height of centralizers has a great influence on the PIP global buckling
F end = Fend /n where n is the number of centralizers in the imperfection segment; Nin is the axial force of the inner pipe; Nout is the axial force of the outer pipe; μ1 is the frictional coefficient between the centering ring and outer pipe; μ2 is the axial frictional coefficient between the outer pipe and seabed; μ3 is the lateral frictional coefficient between the outer pipe and seabed; W is the underwater self-weight of the PIP structure
Summary
With the gradual increase of marine oil and gas exploitation depth, high temperature, high pressure, corrosion effect, and ocean currents are all extreme conditions experienced by subsea pipelines, which result in enormous economic losses and catastrophic and irreversible environmental pollution [1]. The study by Vaz and Patel neglects the two important factors in the theoretical framework of overall buckling, namely, frictional force and initial imperfections Their analysis was only the first step in conducting a global buckling analysis of the PIP structure, and a large quantity of work remains to be improved. Previous studies have focused on theoretical studies, and the proposed computational formulas of buckling critical force of the PIP structure have not considered the influences of initial imperfections, pipe-soil interaction, and centralizers between the inner and outer pipes, for which they have certain limitations. Based on a nonlinear finite element analysis, a parametric study was conducted to analyze the influence of several variables in the lateral buckling of the PIP structure, namely, the initial imperfections, the pipe-soil interaction, and the height and number of centralizers. South China Sea, the formula is shown to have high accuracy, which can provide a corresponding basis for steel pipeline design
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