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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.

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References

Figures

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Fig. 1

Flexible riser structural layers

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Fig. 2

Interlocked steel carcass cross section (dimensions in mm)

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Fig. 3

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

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Fig. 4

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

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Fig. 5

Strain gauges used in the left window

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Fig. 6

Strain gauges used in the central window

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Fig. 7

View of the experimental setup

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Fig. 8

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

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Fig. 9

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

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Fig. 10

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

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Fig. 11

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

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Fig. 12

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

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Fig. 13

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

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Fig. 14

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

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Fig. 15

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

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Fig. 16

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

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Fig. 17

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

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Fig. 18

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

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Fig. 19

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

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Fig. 20

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

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Fig. 21

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

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Fig. 22

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

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Fig. 23

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

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Fig. 24

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

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Fig. 25

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

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Fig. 26

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

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Fig. 27

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

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Fig. 28

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

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Fig. 29

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

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Fig. 30

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

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Fig. 31

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

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