Upheaval buckling behavior of offshore oil pipeline

Ashutosh (AS) Dhar

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: INFRASTRUCTURE - IV Pipelines & Tunnels

ABSTRACT: Offshore oil pipelines generally operate under very high pressure and temperature in order to maintain flow assurance. The high pressure and temperature could significantly increase the longitudinal forces in the pipeline resulting in upheaval bucking, which is one of the key design considerations. Prediction of the upheaval buckling of offshore pipelines is challenging because of number of factors involved including seabed sediment behavior, cover depth, pipe material, and the operating conditions. Different models currently exist in the literature to predict the critical buckling loads that are based on assumed shapes of pipeline imperfection, soil loading, and boundary conditions. However, researchers have demonstrated that the critical load is very sensitive to the imperfection geometry, soil resistance, and end boundary conditions, which are very difficult to be predicted for subsea pipelines. One possible way to deal with the problem is to model the possible scenarios numerically. Numerical modelling of upheaval buckling of subsea pipeline using finite element (FE) method is being used over the past several years to address this issue. Current research progress in this area is mostly limited to simplified imperfection geometries, use of elastic spring for uplift resistance, and fixed end conditions. This paper presents an investigation of upheaval buckling under a realistic imperfection geometries using FE modeling. A parametric study is conducted to investigate the effects of initial shape of imperfection and the pipe cross-sectional property on the upheaval buckling. The universal design curve used to design preventive measure against upheaval buckling is evaluated using FE analysis.

RÉSUMÉ: Offshore oléoducs fonctionnent généralement sous trèla circulation. La haute pression et la température pourraient augmenter significativement les forces longitudinales dans le pipeline entraînant bouleversement à contre-des facteurs clés de la conception. Prédiction de la déformation de bouleversement de pipelines offshore est difficile en raison de nombreux facteurs impliqués, y compris le comportement des sédiments des fonds marins, la profondeur de la couverture, matériau de la conduite et les conditions de fonctionnement. Différents modèles existent actuellement dans la littérature pour prévoir les charges critiques de flambement qui reposent sur des formes supposées de pipeline imperfection, chargement de sol et conditions aux résistance du sol et fin des conditions aux limites, qui sont très difficiles à prévoir pour pipelines sous-marins. Une façon possible de régler le problème est de modéliser les scénarios possibles numériquement. Numérique, modélisation des bouleversements flambage du pipeline sous-dernières années pour régler ce problème. Progrès de la recherche actuelle dans ce domaine sont principalement limité ment de bouleversement. La courbe de la conception universelle utilisée pour la conception de mesure préventive contre des bouleversements flambage est évaluée en INTRODUCTION Offshore oil and gas development activities have grown rapidly over the past few decades to meet the global energy demand. Pipelines, as the most viable mean for transporting oil and gas, is being used worldwide for transporting offshore oil and gas. However, offshore pipeline design faces a number of engineering challenges, which require proper understanding of the behavior of the pipelines on and in the seabed under various operating conditions. Upheaval buckling was recognized as an important design consideration for offshore pipelines in the early 1980s when a few upheaval buckling incidents occurred in the North Sea (Liu and Yan 2013). Upheaval buckling is a mode of pipeline deformation (upward) that overstresses the pipe wall and may lead to fracture (DNV-RP-F101 2007). Such fracture damage in pipelines should be prevented not only to avoid the huge economic loss associated with a system shut-down, repair, and the loss of products, but also to safeguard the environment from the escaping contaminants. Therefore, the prediction of upheaval buckling and protective measures against this phenomenon is very important for offshore pipelines (Liu et al. 2015). The offshore pipeline transporting oil with high internal pressure and high temperature (HP/HT) experiences high compressive force normal to the pipe cross-section when the pipe is constrained along longitudinal direction. The pipe buckles laterally, vertically or obliquely when this

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