Analytical study of distributed buoyancy sections to control lateral thermal buckling of subsea pipelines

Unburied subsea pipelines operating under high temperature and high pressure (HT/HP) conditions tend to relieve their axial compressive force by forming lateral buckles in an uncontrolled manner. In order to control lateral buckling, a distributed buoyancy section is often employed. In this study, analytical solutions are deduced for lateral buckling of unburied subsea pipelines with a distributed buoyancy section. An energy analysis is employed to investigate the stability of the buckled pipeline. The influence of the length and weight of the distributed buoyancy section on pipeline buckled configurations, typical lateral buckling behaviour and the minimum critical temperature difference is illustrated and analysed. The results are shown to be in good agreement with experimental data in the literature. The effect of imperfections is also discussed and an error analysis is conducted for one of the main assumptions of the proposed analytical method. The results show that increasing the length or decreasing the weight of the distributed buoyancy section can both be used to decrease the minimum critical temperature difference. The maximum compressive stress will decrease with decreasing weight of the distributed buoyancy section. However, the influence of the length of the distributed buoyancy section on the maximum compressive stress is complicated.