Nonlinear finite element analysis of collapse and post-collapse behaviour in dented submarine pipelines

• A practical and robust verification method for free-issued offshore pipe sizes beyond the recommended practice limits.
• Analysis considering residual carry-on effects from denting of the pipes.
• Possibilities of applying various shapes and sizes of indentation, depicting actual damaged pipe scenarios.
• Identification of line pipe utilisation factor for continued usage after sustaining damage.
• Comparison with theoretical and available experimental results from previous studies.

The venture of oil and gas exploration into deeper waters has increased drastically in these recent years, as the shallow water fields approaching exhaustion. Large diameter pipelines installed in these areas are exposed to the severe pressure loading resulting from the water depth and any pre-installation damages sustained during transportation or pipelay and may reduce the collapse and buckle propagation resistance drastically. This work focuses on the utilisation and application of the finite element method as a robust and practical engineering tool to establish a methodology for analysing the effects of initial imperfections in the form of dents of various shapes and sizes on pipelines, sustained prior to pipelay, to determine the collapse pressure and buckle propagation pressure which can result in costly abandonments and unnecessary replacements. Comparison between the available theoretical closed-form simplified solutions available via 2D ring analogy, the experimental test conducted by various researchers on steel tubes, empirical formulations from past works and the analysis results obtained from this research were conducted, by incorporating the material plasticity, residual stresses and external pressure. The methodology employed herein provides a relatively realistic and practical assessment tool for computing the collapse and buckle propagation pressures of dented large-diameter submarine pipelines.