Investigation of the buckling behaviour of circumferentially welded pipelines

Barrett, John (John Avery) (2009) Investigation of the buckling behaviour of circumferentially welded pipelines. Masters thesis, Memorial University of Newfoundland.

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Abstract

Many researchers have studied the buckling behaviour of pipelines under combined loading in the interest of defining pipeline capacity as the pipe undergoes large deformation due to extreme ground movement. Past studies have used a number of physical, analytical, and numerical methods in order to understand pipeline behaviour and define the strain limits necessary in limit states design. A review of published works has been presented here as well as two conference papers detailing the calibration of a numerical model and comments on the buckling behaviour of a pipeline. -- The first paper, accepted by OMAE 2009, extensively described the calibration of the numerical model which was used to study the buckling behaviour and capacity of pipelines. This paper had specific interest in the effects of radial offset imperfections, due to girth welding process, on structural capacity. A parametric study also examined diameter, thickness, internal applied pressure and applied axial force. The presence of a compressive axial force was shown to decrease critical moment and strain. Strain capacity was shown to be reduced by as much as 35% depending on the magnitude of girth weld imperfection. Strain behaviour over various pressure levels was shown to be non-linear and shown be reflected in the development of strain based equations. -- The second paper, submitted to CSCE 2009, conducted further analysis on the results generated from the parametric study with a focus on the resultant buckled waveforms and pipeline section ovality. Buckled wavelength and amplitude were influenced by pipeline diameter, diameter to thickness (D/t) ratio and applied internal pressure with limited influence from misalignment amplitude. Ovality, a measure of pipeline out-of-roundness, was found to remain constant over diameter, increase with decreasing D/t, decrease with internal pressure, and remain unaffected by axial force or amplitude of imperfection. End effects were discovered to be a problem when considering pressurized pipes and have been quantified for select cases. This has been shown to be a direct result of the diameter to length ratio of the tested pipeline. As result, it is recommended that the length to diameter ratios for test sections should be as large as practical, for both numerical and physical tests, to avoid boundary effects. -- The numerical procedure developed in this study has shown to be consistent with a number of sources, Ghodsi et al. (1994), Dorey (2001) and Torselletti et al. (2005). The main conclusion and recommendation given as a result of this study was that boundary effects greatly influence the buckling behaviour of the short pipelines studied and that further investigations warrants the use of longer test sections.

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