0
Research Papers: Structures and Safety Reliability

Lazy-Wave Buoyancy Length Reduction Based on Fatigue Reliability Analysis

[+] Author and Article Information
Vinícius Ribeiro Machado da Silva, Luis V. S. Sagrilo, Mario Alfredo Vignoles

Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received June 15, 2017; final manuscript received December 14, 2017; published online February 13, 2018. Assoc. Editor: Carlos Guedes Soares.

J. Offshore Mech. Arct. Eng 140(3), 031602 (Feb 13, 2018) (7 pages) Paper No: OMAE-17-1090; doi: 10.1115/1.4038937 History: Received June 15, 2017; Revised December 14, 2017

The current downturn of the oil and gas industry force managers to take hard decisions about the continuity of projects, resulting in delays, postponements, or even their cancellation. In order to keep with them, the rush for cost reduction is a reality and the industry is pushing the involved parties to be aligned with this objective. The Brazilian presalt region, characterized by ultra-deep waters, faces this scenario where flexible risers in lazy-wave configurations are usually adopted as a solution to safe transfer fluids from sea bed until the floating unit. The smaller the buoyancy length, the cheaper the project becomes, reducing the necessary amount of buoys and the time spent for its installation. This paper investigates the possibility of buoyancy length reduction of lazy-wave configurations by using structural reliability methods on fatigue failure mode. The application of the fatigue reliability approach considers four 6 in flexible riser configurations: an original lazy-wave, a lazy-wave with less 30% of buoyancy length, another one with less 50% of buoyancy length and a free-hanging. Failure probabilities and safety factor calibration curves are shown for each configuration and compared among themselves. The results indicate the possibility of defining a lazy-wave configuration with smaller buoyancy lengths, reaching 75% of reduction without changing the preconized high safety class. Structural reliability analysis is available to help engineers understand the driving random variables of the problem, supporting the actual scenario of cost reduction for better decision-making based on quantified risk.

FIGURES IN THIS ARTICLE
<>
Copyright © 2018 by ASME
Your Session has timed out. Please sign back in to continue.

References

DNV, 2005, “ Recommended Practice—Riser Fatigue,” Det Norske Veritas, Hovik, Norway, Standard No. DNV-RP-F204. http://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2010-10/RP-F204.pdf
DNV, 2010, “ Offshore Standard —Dynamic Risers,” Det Norske Veritas, Hovik, Norway, Standard No. DNV-OS-F201. http://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2010-10/Os-F201.pdf
SINTEF, 2014, “ Handbook on Design and Operation of Flexible Pipes, Joint Industry Project (JIP): Safe and Cost Effective Operation of Flexible Pipes,” SINTEF, Trondheim, Norway, accessed June 3, 2016, http://www.sintef.no/download-handbook
Filho, F. S. L. , 2008, “ Fatigue Analysis Methodology for Flexible Pipes Based on Structural Reliability,” M.Sc. dissertation, COPPE/UFRJ, Rio de Janeiro, Brazil (in Portuguese).
Filho, F. S. L. , Lima, E. C. P. , Sagrilo, L. V. S. , Lima, E. C. P. , and Lemos, C. A. D. , 2012, “ Methodology for Fatigue Analysis in Flexible Pipes Based on Structural Reliability Considering S-N Bilinear Curve,” ASME Paper No. OMAE2012-83585.
Benbow, D. W. , and Broome, H. W. , 2008, The Certified Reliability Engineer, 2nd ed., ASQ Quality Press, Milwaukee, Wisconsin, Chap. 1.
ANP, 2015, “ Operational Safety of Subsea System Management—SGSS,” Resolution 41, Brazilian Regulator Agency of Oil and Gas—ANP, Rio de Janeiro, Brazil.
Silva, V. R. M. , 2015, “ Fatigue Reliability Assessment for Flexible Riser Armour Wires,” ASME Paper No. OMAE2015-41526.
Leira, B. J. , Baarholm, G. S. , Igland, R. T. , Farnes, K. A. , and Percy, D. , 2005, “ Fatigue Safety Factors for Flexible Risers Based on Case Specific Reliability Analysis,” ASME Paper No. OMAE2005-67432.
Melchers, R. E. , 2002, Structural Reliability Analysis and Prediction, 2nd ed., Wiley, Chichester, UK, Chap. 3.
Almar-Naess, A. , 1999, Fatigue Handbook Offshore Steel Structures, Tapir, Trondheim, Norway.
Silva, V. R. M. , 2015, “ Fatigue Reliability Analysis for Armour Wires of Flexible Pipes,” M.Sc. dissertation, COPPE/UFRJ, Rio de Janeiro, Brazil (in Portuguese).
Principia, 2011, “ DeeplinesTM 4.5—Theory Manual,” Principia, La Ciotat, France.
Feret, J. , and Bournazel, C. H. , 1987, “ Calculation of Stresses and Slip in Structural Layers of Unbounded Flexible Pipes,” ASME J. Offshore Mech. Arctic Eng., 109(3), pp. 263–269. [CrossRef]
Feret, J. , Leroy, J. M. , and Estrier, P. , 1995, “ Calculation of Stresses and Slips in Flexible Armour Layers With Layers Interaction,” 14th International Conference on Offshore Mechanics and Arctic Engineering, Copenhagen, Denmark, June 18–22, pp. 469–474.
Vignoles, M. A. , 2002, “ Deterministic and Random Analyses for Fatigue Life Evaluation of Flexible Risers' Metallic Armours,” M.Sc. dissertation, COPPE/UFRJ, Rio de Janeiro, Brazil (in Portuguese).
ASTM, 2011, “ Standard Practices for Cycle Counting in Fatigue Analysis,” American Society of Testing Materials, West Conshohocken, PA, Standard No. E1049-85.
Sousa, J. R. M. , Campello, G. C. , Kwietniewski, C. E. F. , Ellwanger, G. B. , and Strohaecker, T. R. , 2014, “ Structural Response of a Flexible Pipe With Damaged Tensile Armor Wires Under Pure Tension,” Mar. Struct. J., 39, pp. 1–38. [CrossRef]

Figures

Grahic Jump Location
Fig. 1

Flexible risers' configurations of previous study [8]

Grahic Jump Location
Fig. 2

Normalized function for Xi [8]

Grahic Jump Location
Fig. 3

Flexible risers' configurations

Grahic Jump Location
Fig. 4

Fatigue calculation schematic sequence [12]

Grahic Jump Location
Fig. 5

Importance factors for the last year in operation [8]

Grahic Jump Location
Fig. 6

Failure probability behavior due to different amount of random variables

Grahic Jump Location
Fig. 7

Selected random variables

Grahic Jump Location
Fig. 8

pf versus Toper for the four configurations

Grahic Jump Location
Fig. 9

Importance factors for the last year in operation

Grahic Jump Location
Fig. 10

Safety factor behavior of the four configurations

Tables

Errata

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