Session: 04-04-03 Rigid Pipelines III

Submission Number: 182372

Analytical Study of Lateral Buckling Behavior of Pipelines Under Cyclic Loads With Nonlinear Pipe-Soil Interaction 

Unburied subsea pipelines expand and contract under cyclic thermal loads. High-pressure and high-temperature (HPHT) conditions can trigger uncontrolled lateral buckling acting on operating pipelines due to pipe initial imperfections and soil resistance. Due to lateral soil resistance, the pipeline fails to fully revert to its original straight configuration after the heat-up and cooldown procedures. The limit state design approach for pipeline lateral buckling design, as specified in the DNV code, provides detailed limitations on stress, strain, and fatigue damage for pipeline design. Several analytical solutions exist for the buckled pipeline in the operating condition, which can only estimate the maximum stress and strain of the pipeline in the operating condition. There are still no analytical works available to evaluate subsea pipelines in the shut-in condition; therefore, finite element analysis (FEA) is often utilized to investigate pipeline lateral buckling under cyclic thermal loads, including both operating and shut-in conditions, due to the inherent complexity of the problem. However, FEA approach is known to be time-intensive. In this study, an analytical theory describing a symmetric lateral buckling configuration of a pipeline on the seabed with non-linear pipe-soil interaction for both operating and shut-in conditions is derived from differential equilibrium equations for small deformation. The analytical solutions are benchmarked against FEA results, showing that the predicted buckled length, buckle amplitude, and maximum stress/strain deviate by less than 10%. These findings demonstrate that the analytical methodology provides reliable predictions for the limited state checks in the pipeline VAS lateral buckling design. The critical buckling loads, accounting for initial pipeline imperfections, are derived. The effects of feed-in zone length and lateral soil resistance on lateral buckling behavior during both heat-up and cool-down cycles are also discussed. The proposed analytical approaches can be formulated into computational worksheets to support the pipeline lateral buckling design, providing practicing engineers with an efficient and cost-effective alternative for the design of HPHT pipelines.

Presenting Author: Qiang Bai Ocean College, Zhejiang University

Presenting Author Biography: Qiang Bai, PhD, Professor of the Institute of Marine Structures & Naval Architectures, Ocean College, Zhejiang University

Authors:

Qiang Bai Ocean College, Zhejiang University
Shichao Wang Ocean College, Zhejiang University