Analysis of walking rate for subsea pipelines neighbouring the pipeline end terminations/pipeline end manifolds

Abstract

Pipeline walking is a global axial movement caused by the asymmetric distribution of axial force along the pipeline during the repetitive operational loading cycle. The pipeline walking rate, increasing with the loading cycles, may lead to high stress thereby the failure of connectors at PLETs or PLEMs. Current research studies and design guidelines focused on free-end pipelines and neglected changes in the pipeline walking rate and axial resistance with effects of pipeline end structures. However, in practice, several pipelines are adjacent to PLETs or PLEMs, which potentially affect the pipeline walking and expansion behaviour thereby walking rate and axial displacement. This study analyses the walking phenomenon considering the effects of mobilisation of the resistance at the pipeline end structures and develops new analytical solutions for the present problem, in terms of different walking mechanism, maximum axial resistance Pmax, and positions of pipeline end structures. The analytical solutions are validated through numerical simulation results. The case study results indicate the axial resistance generated by PLETs/PLEMs can effectively mitigate pipeline walking rate compared with free-end pipeline walking. In particular, the influence of PLETs/PLEMs is investigated, highlighting the sensitivity of the pipeline walking to the end boundary conditions covering different design scenarios.