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Pipe-In-Pipe system for offshore applications: Post buckling analysis associated with thermal expansion
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The usage of Pipe-In-Pipe (PIP) solutions for offshore applications has increased during the lastyears. The solution gives high thermal insulation and protects the flow line from environmental impacts. One critical load case is buckling of the pipeline system due to thermal expansions of the inner pipe. This project intends to increase knowledge about PIP systems, investigate the impact of different parameters as well as update parameters in an existing SIMLA model. A FE-model of a PIP system was created in ANSYS with a refined section where pipes and centralizers are modelled with solid elements.The ANSYS-model was tested against a verified FE-model created in SIMLA. The global results obtained from ANSYS and SIMLA did not give a perfect match. The ANSYS model tended to buckle in another way, which is assumed to be related to different modelling of resistance between the pipeline and the seabed as well as unwished properties between the side section and the midsection.Local results obtained from ANSYS showed that there are discontinuities in bending moment and effective axial forces when passing a centralizer. The contact force between centralizer and pipes give rise to high friction forces that acts along the same line as the axial force in the pipes.Increased friction coefficient between centralizer and outer pipe resulted in increased discontinuity in axial force. Selection of a proper friction coefficient thus has significant influence on the results.Centralizer stiffness was evaluated by a local FE-model where a centralizer was compressed between the inner and the outer pipe. Displacement of inner pipe was evaluated as a function of applied force. The result showed that the force-displacement curve describing centralizer stiffness follows 

 Q (Δ)=( Δ) 

where      is a constant depending on dimensions and material of the centralizer. Linearized indifferent sections and with a centralizer thickness of 0,1 meter the following expression gave stiffnesses in the range 100-1000 MN/m, which agrees with stiffnesses used in the SIMLA model.displacements up to 0.3 mm the radial stiffness used in SIMLA is still good to use.

Place, publisher, year, edition, pages
2014. , 92 p.
TRITA-AVE, ISSN 1651-7660 ; 2014:27
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-177312OAI: diva2:872195
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2015-11-18Bibliographically approved

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