Particular Aspects Regarding the Lateral Buckling Analysis of Flowlines

The paper is concerned with the analysis of the effects of lateral buckling along a flowline. The analysis is considered to be relevant to the early stages of design, i.e. typically pre-FEED, and specifically addresses the significant effect that material strength properties has on the calculation of maximum strains along a flowline that could develop lateral deformations due to high temperature operating conditions. The analysis approach used here to generate the results presented in the paper is based on the assumed distances between sites of lateral buckling. This is generally known as the virtual anchor spacing (VAS). It is also assumed that the assessment of the acceptability of the deformations and the calculated maximum strain levels, with regard to the safety of the operating flowline, may validly be based on the displacement controlled methodology contained in guidance prepared by DNV. It is shown that the interaction between the material properties and the levels of lateral friction results in an ambiguity with regard to the relevant displacement patterns that can occur along the flowline at the site of a lateral buckle. It is concluded that the calculation models used even during early stages of design, should be based on the relevant pipe material properties and that compromise with these properties, perhaps to improve the stability of the numerical modelling, should be avoided. Another conclusion from the results relates to the assumption of symmetry boundary conditions in finite element and other models since this assumption could possibly underestimate the calculated levels of the maximum strain at the lateral buckle and thus undermine the use of the displacement controlled approach to safety assessment.