Asymmetric buckling of offshore pipelines under combined tension, bending and external pressure

Abstract

The seamless steel pipes inevitably incorporate various initial geometric imperfections introduced in the manufacturing process. The offshore pipelines close to the touch-down point in the sagbend have to withstand the combined actions of axial tension, bending and external pressure during deepwater installation. In this paper, a two-dimensional (2D) theoretical formulation is further developed to investigate the asymmetric buckling behaviour of offshore pipelines with arbitrary initial geometric imperfections under complicated loading conditions. In addition, numerical simulations based on a 3D finite-element model of the imperfect tube using the software ABAQUS are carried out. Close agreement between the results demonstrates the effectiveness and practicality of this theoretical method. The theoretical model is then employed to study the effects of some important influencing factors such as initial geometric imperfections represented by initial ovality and wall eccentricity, ovality orientation, material properties represented by effective yield stress and strain-hardening parameter, diameter-to-thickness ratio, axial tension, and load cases on the buckling behaviour of the imperfect tubes. Based on extensive parametric studies, some significant conclusions were drawn.