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Pipeline Walking of High Pressure/Temperature Flowlines
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

The offshore pipeline industry are facing more complex design challenges as the oil and gas industry moves into deeper water in search for hydrocarbons. One of these challenges are related to high pressure/high temperature pipelines subjected to frequent start-up and shut-downs during its? lifetime. One consequence of this kind of load cycles is that the pipeline may move cycle wise and axially towards its? cold end, which may be detrimental for the end connection design. This phenomenon is termed pipeline walking. The SAFEBUCK Joint Industry Project was initiated in 2002 to assess the challenges connected to pipeline walking, in addition to other related issues. Through this project several aspects affecting the walking behaviour have been established. These factors have, in this thesis, been addressed through a sensitivity analysis, where the seabed conditions ? hereby the equivalent friction factor ? the seabed slope, the effect of a global lateral buckle and the effect of a connected SCR have been included. The sensitivity study was performed on a pipeline modelled in SIMLA with 900 beam elements, each connected with a spring to a seabed beam element. This original case have here been labelled the base case. Four cases were analysed, were one factor were changed throughout each of the cases. The pipeline was subjected to a transient temperature profile in each case, provided by IKM Ocean Design, to simulate the heat transfer in a pipeline. For the seabed conditions case, the walk per load cycle increased with increasing equivalent friction factor up to a certain point, before the walk per load cycle decreased as the equivalent friction factor continued to increase. The seabed slope case showed that the relationship between walk per cycle and increasing angle is approximately linear. In addition it was established that when the seabed slope is steep enough, the pipeline will walk towards its? warm end. In the global lateral buckle case on could observe that the effective axial friction force was relieved in the buckle, and that the walk per cycle increased as the length of the buckle increased. When a steel catenary riser tension was introduced, the axial movement of the pipeline appeared to fluctuate around the walk per cycle values for the base case. An analytical analysis was performed, however, the accordance between the numerical and analytical results was not as good as predicted. For this reason an improvement of the analytical model is suggested for further work. An other topic which is relevant for further work is an extension of the seabed conditions case to include mobilisation length. Additional sub-cases in the steel catenary riser case, as well as creating a new case by combining the impact from several walking inducing factors are other possible topics.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2013. , 116 p.
URN: urn:nbn:no:ntnu:diva-22366Local ID: ntnudaim:9144OAI: diva2:649609
Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2013-09-19Bibliographically approved

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