Feasibility Study of Lateral Buckling Using Residual Curvature Method for Deep Water Pipelines

In recent years the residual curvature (RC) method has been used to provide buckle initiators to control and mitigate the lateral buckling of pipelines for some shallow water projects. With the appropriate planning of the controlled buckles using RC sections, an acceptable design of the pipeline in-place behavior is achieved. However, the RC method has not yet been applied to deep-water pipelines. The twist of RC sections in the sagbend during installation has been observed, and the orientation of as-laid RC section on the seabed is difficult to control in deep-water pipelines. The effects of as-laid RC-section orientation on in-place lateral buckling in deep water are unknown. The FRIC user subroutine in the Abaqus finite-element software suite has been developed for modelling pipe-soil interactions based on uncoupled axial and lateral soil resistances that are assumed to be independent of vertical pipe penetration after initial embedment into the soil surface. However, the penetration of a twisted RC section can vary dramatically from a normal pipeline on the seabed. The UINTER user subroutine in Abaqus was selected for presenting 3D pipe-soil interactions that incorporate the variations of independent axial and lateral soil resistances as a function of pipe penetration more accurately. UINTER is used in the present study to account for the effects of soil penetration on the lateral buckling performance of a pipeline with RC sections in soft clay. The analysis results show that the RC section twists in the sagbend area during installation, and the twist angle reaches its maximum value just prior to the RC section touching the seabed. The in-place lateral buckling analysis is carried out after the installation analysis is finished. The analysis results demonstrate the feasibility of applying the RC method as the primary buckle triggering mechanism for deep water pipelines, and it shows how the RC orientation affects the pipeline in-place performance in terms of strength and fatigue damage (only the stress ranges for use in fatigue calculations are shown in the paper).