In-Place FE Modeling of Unbonded Flexible Pipelines Capturing Pressure Stiffening and Decoupled Axial/Nonlinear Bending Stiffness

2010 ◽  
Author(s):  
Edvin Hanken ◽  
Evelyn R. Hollingsworth ◽  
Lars S. Fagerland
Keyword(s):  
Water Injection ◽  
Bending Stiffness ◽  
Axial Stiffness ◽  
Fe Model ◽  
Nonlinear Bending ◽  
Upheaval Buckling ◽  
History Effects ◽  
System Integrity ◽  
Non Linear ◽  
Bending Behaviour

For fast track pipeline projects the need for costly installation vessels and sophisticated materials for rigid pipeline water injection systems, have made flexible pipelines a competitive alternative. They can be installed with less costly construction vessels, provide a competitive lead time and a corrosion resistant compliant material. Flexible pipelines have relative high axial stiffness and low non-linear bending stiffness which is a challenge to model correctly with FE for in-place analyses of pipelines. Whilst some FE programs can model the non-linear bending behaviour of a flexible pipeline at a given pressure, current FE tools do not include the effect of increased bending resistance as the system is pressurized. Therefore, a 3D FE model in ANSYS was developed to simulate the decoupled axial and nonlinear bending behaviour of a flexible, including the bend stiffening effect for increasing pressure. A description of the model is given in this paper. It will be demonstrated how the FE model can be used to simulate the 3D nonlinear catenary behaviour of an high pressure flexible pipeline tied into a manifold during pressurization. Due to high manifold hub loads during pressurization it is essential that such a model is capable of capturing all effects during pressurization to achieve an acceptable confidence level of the system integrity. It is also described how the FE model is used for upheaval buckling design, capturing non-linearities and load history effects that can reduce the conservatism in the design.

Large-Scale Tests for Identifying the Nonlinear, Temperature-Sensitive, and Frequency-Sensitive Bending Stiffness of the NordLink Cable

2017 ◽  
Author(s):  
Magnus Komperød ◽  
Jon Ivar Juvik ◽  
Gunnar Evenset ◽  
Roger Slora ◽  
Lars Jordal
Keyword(s):  
Large Scale ◽  
Bending Moment ◽  
Bending Stiffness ◽  
Temperature Sensitive ◽  
Nonlinear Bending ◽  
Hvdc System ◽  
High Voltage Direct Current ◽  
Highly Nonlinear ◽  
Industry Practice ◽  
Large Scale Tests

The NordLink project is a cooperation between Statnett, TenneT, and KfW to build a subsea High Voltage Direct Current (HVDC) system between Norway and Germany. The cables are produced by Nexans Norway and ABB. This paper presents the main results of 30 bending stiffness tests run on the NordLink cable using a novel, dynamic bending stiffness test rig developed by Nexans. It is concluded that there is a highly nonlinear bending moment vs. bending curvature relationship. Also, this relationship is most sensitive to the temperature and somewhat sensitive to the frequency of the cable oscillations. Within a realistic range of curvature amplitudes, temperatures, and frequencies, the bending stiffness varies from 12 to 124 kNm2. These observations strongly suggest that the common industry practice of using a constant bending stiffness should be abandoned.

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