Uplift Resistance of Offshore Pipelines Subject to Upheaval Buckling

Abstract

Offshore pipelines that transport oil and gas in different areas in the world are often buried in trenches to provide stability and protection against upheaval buckling. Hydrocarbons in the pipeline are transported at high temperatures and pressures to facilitate the oil flow and prevent its solidification. However, this mode of transport causes an increase in the axial compressive forces inside the pipeline which may lead to upward buckling in the direction of the least soil resistance. Upheaval buckling can result in pipeline failure causing severe environmental and economic losses. In this paper, a 3D parametric study of upheaval buckling of pipelines buried in medium dense sand with fines is performed using the finite element software Abaqus©. The effects of pipeline diameter, embedment depth ratio and diameter to wall thickness ratio on the soil resistance against uplift are investigated for pipeline pullout cases simulating plane strain conditions. The results are compared with the available analytical/empirical solutions for the uplift resistance. The results show that the uplift resistance depends in part on the pipeline diameter and embedment depth ratio. The available design methods which assume mobilized soil blocks above the pipeline with inclined slip surfaces better capture the behavior observed in the numerical models, as compared to those methods in which vertical slip surfaces are considered.