0
Research Papers: Piper and Riser Technology

Some Further Studies on the Axial–Torsional Behavior of Flexible Risers

[+] Author and Article Information
Roberto Ramos, Jr.

e-mail: rramosjr@usp.br

Clóvis A. Martins

e-mail: cmartins@usp.br

Celso P. Pesce

e-mail: ceppesce@usp.br
University of São Paulo–Escola Politécnica,
Mech. Eng. Department,
05508-970, Av. Prof. Mello Moraes 2231,
São Paulo, Brazil

Francisco E. Roveri

Petrobras– CENPES,
21941-915, Av. Horácio Macedo, 915,
Rio de Janeiro, Brazil
e-mail: roveri@petrobras.com.br

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received September 14, 2010; final manuscript received September 2, 2013; published online November 12, 2013. Assoc. Editor: Pingsha Dong.

J. Offshore Mech. Arct. Eng 136(1), 011701 (Nov 12, 2013) (11 pages) Paper No: OMAE-10-1093; doi: 10.1115/1.4025541 History: Received September 14, 2010; Revised September 02, 2013

Flexible risers are complex structures composed of several concentric polymeric and steel armor layers that withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the response of these structures when subjected to axisymmetric loadings (i.e., any combination of traction, torsion, and internal or external pressures) is an important task for the local structural analysis since it provides probable values for the loading distribution along the layers and, thus, allowing estimating the expected life of a riser using fatigue tools. Although finite element models have been increasingly used to accomplish this task in the last years, the simplicity and the reasonable accuracy provided by analytical models can be seen as reasons that justify their continued use, at least in the initial cycles of the design. However, any analytical model proposed for such a task must be checked with well-conducted experimental results in order to be considered as an acceptable analysis tool. The aims of this article are twofold: (i) to present the main results of experimental tests involving both internal pressure and traction loadings on a 63.5 mm (2.5 in.) flexible riser, carried out at the Institute for Technological Research of São Paulo (IPT), which can be used as a means of checking finite element or analytical models proposed by other researchers, and (ii) to compare some results obtained experimentally with those predicted by an analytical model which can also include any combination of axisymmetric loadings. Besides presenting full data concerning the internal structure of the riser, the experimental procedures used to perform the tests and the main results (e.g., Force × Displacement curves) are also presented. A brief discussion about the validity of some hypotheses that are usually assumed by analytical models found in the technical literature is made.

Copyright © 2014 by ASME
Your Session has timed out. Please sign back in to continue.

References

Knapp, R. H., 1979, “Derivation of a New Stiffness Matrix for Helically Armoured Cables Considering Tension and Torsion,” J. Num. Meth. Eng., 14, pp. 515–529. [CrossRef]
Costello, G. A., 1997, Theory of Wire Rope, 2nd ed., Springer, New York.
Lanteigne, J., 1985, “Theoretical Estimation of the Response of Helically Armored Cables to Tension, Torsion and Bending,” ASME J. Appl. Mech., 52, pp. 423–432. [CrossRef]
Akhtar, A., and Lanteigne, J., 1998, “Evaluation of Tensile Strength of Multistrand Conductors—Part I: Theoretical Basis,” ASME J. Eng. Mater., 120, pp. 33–38. [CrossRef]
Akhtar, A., and Lanteigne, J., 1998, “Evaluation of Tensile Strength of Multistrand Conductors—Part II: Experimental Results,” ASME J. Eng. Mater., 120, pp. 39–47. [CrossRef]
Feret, J. J., and Bournazel, C. L., 1987, “Calculation of Stresses and Slip in Structural Layers of Unbonded Flexible Pipes,” ASME J. Offshore Mech. Arct., 109, pp. 263–269. [CrossRef]
Witz, J., and Tan, Z., 1992, “On the Axial-Torsional Structural Behaviour of Flexible Pipes, Umbilicals and Marine Cables,” Marine Struct., 5, pp. 205–227. [CrossRef]
Witz, J., and Tan, Z., 1992, “On the Flexural Structural Behaviour of Flexible Pipes, Umbilicals and Marine Cables,” Marine Struct., 5, pp. 229–249. [CrossRef]
Witz, J. A., 1996, “A Case Study in the Cross-Section Analysis of Flexible Risers,” Marine Struct., 9, pp. 885–904. [CrossRef]
Custódio, A. B., and Vaz, M. A., 2002, “A Nonlinear Formulation for the Axisymmetric Response of Umbilical Cables and Flexible Pipes,” Appl. Ocean Res., 24, pp. 21–29. [CrossRef]
Vaz, M. A., Aguiar, L. A. D., Estefen, S. F., and Brack, M., 1998, “Experimental Determination of Axial, Torsional and Bending Stiffness of Umbilical Cables,” Proc. 17th Int. Conf. on Off. Mech. and Arct. Eng., OMAE 1998, Lisbon, OMAE98-0423.
Bahtui, A., Bahai, H., and Alfano, G., 2008, “A Finite Element Analysis for Unbonded Flexible Risers Under Axial Tension,” Proc. 27th Int. Conf. on Off. Mech. and Arct. Eng., OMAE 2008, Estoril, OMAE2008-57627.
Bahtui, A., Bahai, H., and Alfano, G., 2008, “A Finite Element Analysis for Unbonded Flexible Risers Under Torsion,” ASME J. Offshore Mech. Arct., 130, p. 041301. [CrossRef]
Merino, H. E. M., Sousa, J. R. M., Magluta, C., and Roitman, N., 2009, “On the Coupled Extensional-Torsional Response of Flexible Pipes,” Proc. 28th Int. Conf. on Off. Mech. and Arct. Eng., OMAE 2009, Honolulu, HI, OMAE2009-79468.
Neto, A. G., Martins, C. A., Pesce, C. P., Meirelles, C. O. C., Malta, E. R., Neto, T. F. B., and Godinho, C. A. F., 2013, “Prediction of Burst in Flexible Pipes,” ASME J. Offshore Mech. Arct., 135, p. 011401. [CrossRef]
Neto, A. G., and Martins, C. A., 2012, “A Comparative Wet Collapse Buckling Study for the Carcass Layer of Flexible Pipes,” ASME J. Offshore Mech. Arct., 134, p. 031701. [CrossRef]
Ramos, Jr., R., Martins, C. A., Pesce, C. P., and Roveri, E. F., 2008, “A Case Study on the Axial-Torsional Behavior of Flexible Risers,” Proc. ASME 27th Int. Conf. Off. Mech. Arct. Eng., Estoril, Portugal, OMAE2008, 11 p.
Ramos, Jr., R., and Pesce, C. P., 2004, “A Consistent Analytical Model to Predict the Structural Behavior of Flexible Risers Subjected to Combined Loads,” ASME J. Offshore Mech. Arct., 126, pp. 141–146. [CrossRef]
Jolicoeur, C., and Cardou, A., 1991, “A Numerical Comparison of Current Mathematical Models of Twisted Wire Cables Under Axisymmetric Loads,” ASME J. Energ. Resour., 113, pp. 241–249. [CrossRef]
Sathikh, S., Moorthy, M. B. K., and Krishnan, M., 1996, “A Symmetric Linear Elastic Model for Helical Wire Strands Under Axisymmetric Loads,” J. Strain Anal., 31, pp. 389–399. [CrossRef]
Maranhão, F. A. F., 2011, “A Comparative Study of Models for the Local Analysis of Flexible Pipes,” M.Sc. dissertation, University of São Paulo, São Paulo, Brazil, (in Portuguese), http://www.teses.usp.br
Elata, D., Eshkenazy, R., and Weiss, M. P., 2004, “The Mechanical Behavior of a Wire Rope With an Independent Wire Rope Core,” Int. J. Sol. Struct., 41, pp. 1157–1172. [CrossRef]
Young, W. C., and Budynas, R. G., 2002, Roark ´s Formulas for Stress and Strain, 7th ed., McGraw-Hill Inc., New York, Chap. 4.

Figures

Grahic Jump Location
Fig. 1

Flexible riser structural layers

Grahic Jump Location
Fig. 2

Interlocked steel carcass cross section (dimensions in mm)

Grahic Jump Location
Fig. 3

F × t and ΔL × t curves for load case A2 (no internal pressure and ends PFR)

Grahic Jump Location
Fig. 4

Top view of the windows cut from the external plastic layer (dimensions in mm)

Grahic Jump Location
Fig. 5

Strain gauges used in the left window

Grahic Jump Location
Fig. 6

Strain gauges used in the central window

Grahic Jump Location
Fig. 7

View of the experimental setup

Grahic Jump Location
Fig. 8

Force × Elongation curve (load case A1: no internal pressure and ends PFR)

Grahic Jump Location
Fig. 9

Force × Elongation curve (load case A2: no internal pressure and ends PFR)

Grahic Jump Location
Fig. 10

Torque × Elongation curve (load case A1: no internal pressure and ends PFR)

Grahic Jump Location
Fig. 11

Torque × Elongation curve (load case A2: no internal pressure and ends PFR)

Grahic Jump Location
Fig. 12

Force × Elongation curve (load case B1: no internal pressure and ends FTR)

Grahic Jump Location
Fig. 13

Force × Elongation curve (load case B2: no internal pressure and ends FTR)

Grahic Jump Location
Fig. 14

Twisting angle per unit length × Elongation curve (load case B1: no internal pressure and ends FTR)

Grahic Jump Location
Fig. 15

Twisting angle per unit length × Elongation curve (load case B2: no internal pressure and ends FTR)

Grahic Jump Location
Fig. 16

Force × Elongation curve (load case C1: internal pressure and ends PFR)

Grahic Jump Location
Fig. 17

Force × Elongation curve (load case C2: internal pressure and ends PFR)

Grahic Jump Location
Fig. 18

Torque × Elongation curve (load case C1: internal pressure and ends PFR)

Grahic Jump Location
Fig. 19

Torque × Elongation curve (load case C2: internal pressure and ends PFR)

Grahic Jump Location
Fig. 20

Force × Elongation curve (load case D1: internal pressure and ends FTR)

Grahic Jump Location
Fig. 21

Force × Elongation curve (load case D2: internal pressure and ends FTR)

Grahic Jump Location
Fig. 22

Twisting angle per unit length × Elongation curve (load case D1: internal pressure and ends FTR)

Grahic Jump Location
Fig. 23

Twisting angle per unit length × Elongation curve (load case D2: internal pressure and ends FTR)

Grahic Jump Location
Fig. 24

Strains (left window) × Force (load case A1)

Grahic Jump Location
Fig. 25

Strains (central window) × Force (load case A1)

Grahic Jump Location
Fig. 26

Strains (right window) × Force (load case A1)

Grahic Jump Location
Fig. 27

Strain (mean of experimental values and analytical prediction) × Force curves (load case A1)

Grahic Jump Location
Fig. 28

Strains (left window) × Force (load case C1)

Grahic Jump Location
Fig. 29

Strains (central window) × Force (load case C1)

Grahic Jump Location
Fig. 30

Strains (right window) × Force (load case C1)

Grahic Jump Location
Fig. 31

Strain (mean of experimental values and analytical prediction) × Force curves (load case C1)

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In