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.
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June 2018
Research-Article
Lazy-Wave Buoyancy Length Reduction Based on Fatigue Reliability Analysis
Vinícius Ribeiro Machado da Silva,
Vinícius Ribeiro Machado da Silva
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
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Luis V. S. Sagrilo,
Luis V. S. Sagrilo
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Search for other works by this author on:
Mario Alfredo Vignoles
Mario Alfredo Vignoles
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Search for other works by this author on:
Vinícius Ribeiro Machado da Silva
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Luis V. S. Sagrilo
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
Mario Alfredo Vignoles
Civil Engineering Program/COPPE,
Federal University of Rio de Janeiro/COPPE,
Rio de Janeiro 21945-970, Brazil
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. Jun 2018, 140(3): 031602 (7 pages)
Published Online: February 13, 2018
Article history
Received:
June 15, 2017
Revised:
December 14, 2017
Citation
da Silva, V. R. M., Sagrilo, L. V. S., and Vignoles, M. A. (February 13, 2018). "Lazy-Wave Buoyancy Length Reduction Based on Fatigue Reliability Analysis." ASME. J. Offshore Mech. Arct. Eng. June 2018; 140(3): 031602. https://doi.org/10.1115/1.4038937
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