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

Abstract

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.

Analytical study of third-mode lateral thermal buckling for unburied subsea pipelines with sleeper

“…( 9), the axial compressive force in the entire buckled region 0 ≤ ≤ 3 is constant and equal to the force P at the centre of the buckle. The same approximation was made by Hobbs [9,36,39]. An error analysis shows that the assumption of constant axial compressive force for the calculation of lateral deflection is acceptable [36,39].…”

“…The single-buoyancy method was further studied by Shi and Wang [5]. Analytical solutions were derived based on the first lateral buckling mode by Wang et al [34] and on the third lateral buckling mode by Li et al [35] and Wang et al [36] for a pipeline section with a distributed buoyancy section. An analytical solution for controlled lateral buckling of unburied subsea pipelines was studied by Wang et al with the consideration of interaction between adjacent buckles [4].…”

Effect of proximity of imperfections on buckle interaction in deep subsea pipelines

“…4. It should be noted that unlike upheaval buckling response, which is sensitive to the assumed shape of the initial imperfection (because of initial state of stress in the pipe) [8,31], in lateral buckling the pipe is initially unstressed and the deformed shape quickly takes one of the Hobbs' mode shapes [32,33]. Therefore, assuming imperfections of sinusoidal shape will not affect the accuracy of results.…”

Line-Element Formulation for Upheaval Buckling Analysis of Buried Subsea Pipelines Due to Thermal Expansion

“…Nevertheless, such design consideration is sometimes difficult because it is significantly affected by several crucial factors, including the initial out-of-plumpness of pipelines, the depth of buried soils, and the tightness of seabed etc., leading to the rigorous analysis of upheaval buckling difficult. This topic has gained continuous attentions and studied by several researchers for a decade [7][8][9][10][11], which is still popular up to date. Experiments on studying subsea buried pipeline buckling have been initiated in the mid-1990s.…”