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TECHNICAL PAPERS

Initial Crack Depth and POD Values Inferred From In-Service Observations of Cracks in North Sea Jackets

[+] Author and Article Information
Torgeir Moan

Department of Marine Structures, Norwegian University of Science and Technology, 7034 Trondheim, Norway

Ole T. Vårdal, Nils-C. Hellevig, Knut Skjoldli

Aker Offshore Partner, Bergen, Norway

J. Offshore Mech. Arct. Eng 122(3), 157-162 (Apr 14, 2000) (6 pages) doi:10.1115/1.1286676 History: Received March 02, 2000; Revised April 14, 2000
Copyright © 2000 by ASME
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References

Moan, T., 1994, “Reliability and Risk Analysis for Design and Operations Planning of Offshore Structures” in Structural Safety and Reliability, Schuëller, G.I., Shinozuka, M., and Yao, J. T. P., eds., Proc. 6th ICOSSAR Conf., A. A. Balkema, Rotterdam, pp. 21–43.
Kirkemo, F., 1989, “PIA Theory Manual,” Aker, Oslo, Norway.
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Veritas Sesam System, 1989–1992, “Theory, Example, Distribution Manual for the PROBAN Analysis Program,” A. S. Veritas Research, Oslo, Norway.
Vȧrdal, O. T., and Moan, T., 1997, “Predicted versus Observed Fatigue Crack Growth. Validation of Probabilistic Fracture Mechanics Analysis of Fatigue in North Sea Jackets,” Proc., 16th OMAE, Paper No. 1334, Yokohama, Japan.
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Winkworth, W. J., and Fisher, P. J., 1992, “Inspection and Repair of Fixed Platforms in the North Sea,” Paper No. OTC 6937, Offshore Technology Conference, Houston, TX.
Silk, M. G., Stoneham, A. M., and Temple, J. A. G., 1987, “The Reliability of Non-Destructive Inspection,” Adam Hilger, Bristol.
Barnouin, B., et al., 1993, “Underwater Inspection Reliability Trials for Offshore Structures,” Proc., 12th OMAE, Vol. IIIB, Materials Engng., pp. 883–890.
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Figures

Grahic Jump Location
Total number of 690 fabrication and fatigue cracks, as arranged by crack depth
Grahic Jump Location
Probability density function fA(a), probability of crack detection function PD(a) and distribution of detected cracks fA,D1(a) plotted in the same figure. λ=1.95 mm (POD) and λ0=0.94 mm (mean initial crack size). The bars plotted represent the observed frequency of fabrication cracks. The bars to be compared with the distribution of detected cracks fA,D1(a).
Grahic Jump Location
Back calculated initial crack size based on 144 cracks judged as fatigue crack. Method 1 presented in Section 3.2 is applied. The prior distribution of initial crack depth is assumed to be uniform over the interval 0–3 mm and the posterior distribution is fitted to an exponential distribution with parameter λ0=1.0 mm.

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