Asymmetric loading/unloading profiles during the start-up and shut-down operations of high pressure high temperature pipelines may cause an accumulated axial displacement over several operational cycles known as Pipeline Walking phenomenon. This pipeline walking can be triggered by several factors e.g. the seabed slope, riser tension and thermal transients. Several studies have been carried out in the literature regarding the influence from individual factors; nevertheless, very little has been made in the evaluation of coupled triggering mechanisms, common for a pipeline segment.
This paper investigates the pipeline walking phenomenon using finite element modelling and analysis software SAGE Profile 3D versus standard analytical formulae. The keys aims are (i) to study the interaction and coupling between the walking triggering mechanisms by comparing coupled and uncoupled analyses, and (ii) to compare the obtained numerical results with analytical predictions, commonly used in the subsea industry. Depending on the pipeline and soil properties, the effect of triggering mechanisms is parametrically investigated with varying pipeline tension and seabed slope for a specific thermal gradient profile.
It is found that the common approach to sum up the individual walking rate by the uncoupled analysis for a combination of any two triggering mechanisms, underestimates the walking phenomenon when compared with the coupled analysis. This highlights how attention must be paid to the interaction mechanism. In addition, this study emphasizes that the analytical models severely overestimate the pipeline walking phenomenon, especially when more than one triggering mechanisms are present.