Deepwater Flexible Risers and Pipelines. Yong Bai
Чтение книги онлайн.
Читать онлайн книгу Deepwater Flexible Risers and Pipelines - Yong Bai страница 34
Название: Deepwater Flexible Risers and Pipelines
Автор: Yong Bai
Издательство: John Wiley & Sons Limited
Жанр: Физика
isbn: 9781119322733
isbn:
(4.15)
(4.16)
Figure 4.28 MSFP-based reinforced longitudinal profile.
Tensile forces comparison for those pipes with three different configurations is shown in Figure 4.29. As expected, the strength provided by MSFP is the lowest. In fact, for the same inner diameter, the MSFP shows a decrement in axial resistance equal to 81.07% compared to the case which includes two tensile armor layers. At the same time, it is possible to see the improvement in terms of tensile capacity when the pressure armor is included in the MSFP design equal to 81.53%, which results from the comparison between Case 1 and Case 2. When both the pressure and tensile armor layers are included in the design, the high strength in radial direction is not only provided by the pressure armor but also by the tensile armor due to its relevant thickness. Thus, reducing the thickness of the wires not only affects the tensile capacity itself but also the loss of the external capacity.
Figure 4.29 Tensile force comparison.
Being the elongation of the pipe strictly related to its weight, which mostly depends on the amount of the reinforcement needed as well as the water depth, it is possible to assert that the steel strip reinforcements in terms of axial strength of the pipe are suitable for shallow waters. On the other hand, the contribution of thick steel wires is suitable for extreme loading conditions such as for deep water design. It is noteworthythat for both Cases 2 and 3, the contribution of the radial stiffness induced by pressure armor plays an important role in terms of axial capacity of the pipe.
4.6 Conclusions
In this chapter, an easy theoretical method for estimating the tensile stiffness of the unbonded flexible pipe is verified by numerical simulations. Secant modulus is employed in order to carry out the plastic behavior of the material, and this theoretical model is suitable for high loading conditions, which can provide relatively accurate tensile strength for pipeline engineers. The following conclusions could be drawn.
When considering both pressure and tensile armor layers in the pipe’s profile, the external pressure will not have very big impact on its tensile capacity as the radial stiffness of the pressure armor are large enough to resist the radial deformation induced by external pressure.
MSFP is only suitable for shallow water application. Adding a certain profile of pressure armor into MSFP leads to a significant increase in terms of resistance capacity (about eight times). In order to avoid material waste, the profile of the pressure armor could be adjusted according to the water depth, and this can make MSFP exploitable for deeper water depth.
Tangent modulus should be used for next works in order to obtain more accurate results. The contribution of the interlocked carcass should also be taken into account in future works, to verify whether its radial stiffness leads to a remarkable increasing tensile capacity of the pipe.
References
1. Fergestad, D., Løtveit, S. A., ‘Handbook on Design and Operation of Flexible Pipes’, NTNU, 4Subsea and MARINTEK, 2014.
2. Bai, Liu T, et al. Buckling stability of steel strip reinforced thermoplastic pipe subjected to external pressure[J]. Composite Structures 152(2016)528–537.
3. Bai Y, Liu T, et al. Mechanical behavior of metallic strip flexible pipe subjected to tension[J]. Composite Structures, 170(2017)1–10.
4. Knapp, R. H. (1975, September). Nonlinear analysis of a helically armored cable with nonuniform mechanical properties in tension and torsion. In OCEAN 75 Conference (pp. 155–164). IEEE.
5. Knapp, R. H. “Derivation of a new stiffness matrix for helically armoured cables considering tension and torsion.” International Journal for Numerical Methods in Engineering 14. 4(1979): 515–529.
6. Feret, J. J., and C. L. Bournazel. “Calculation of stresses and slip in structural layers of unbonded flexible pipes.” Journal of Offshore Mechanics and Arctic Engineering 109. 3(1987): 263–269.
7. Ramos, R., Martins, C. A., Pesce, C. P., etc. Some further studies on the axial–torsional behavior of flexible risers[J]. Journal of Offshore Mechanics and Arctic Engineering, 2014, 136(1): 1–11.
8. Ramos, R., Kawano, A. Local structural analysis of flexible pipes subjected to traction, torsion and pressure loads[J]. Marine Structures, 2015, 42(1): 95–114.
9. Sævik, S., Bruaseth, S. Theoretical and experimental studies of the axisymmetric behaviour of complex umbilical cross-sections[J]. Applied Ocean Research, 2005, 27(2): 97–106.
10. Sævik, S. Theoretical and experimental studies of stresses in flexible pipes[J]. Computers & Structures, 2011, 89(23): 2273-2291.
11. Sævik, S., Gjøsteen, J. Strength analysis modelling of flexible umbilical members for marine structures[J]. Journal of Applied Mathematics, 2012, 2012(1): 1-18.
12. Dong L, Zhang Q, Huang Y. Energy approaches based axisymmetric analysis of unbonded flexible risers[J]. Huazhong Keji Daxue Xuebao (Ziran Kexue Ban)/J Huazhong Univ Sci Technol (Nature Science Edition)2013;41(5).
13. Guo Y, Chen X, Fu S, Wang D. Mechanical Behavior Analysis for Unbonded Umbilical under Axial Loads[J]. Journal of Ship Mechanics, 1007-7294(2017) 06-0739-11.
14. de Sousa, JoséRenato M., et al. “Structural response of a flexible pipe with damaged tensile armor wires under pure tension.” Marine Structures 39(2014): 1–38.
15. Yue, Qianjin, et al. “Tension behavior prediction of flexible pipelines in shallow water.” Ocean Engineering 58(2013): 201–207.
16. Jiang, K., Liu, T., Yuan, S., & Bai, Y. (2018, June). Mechanical Behaviors of Metallic Strip Flexible Pipe Under Axisymmetric Loads. In ASME2018 37th International Conference on Ocean, Offshore and Arctic Engineering (pp. 005T04A010-V005T04A010).
СКАЧАТЬ