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The Recent Development on the Non-Destructive Inspection Reliability and Its Applications in Offshore Structural Integrity Analysis

  • J. C. P. Kam

Abstract

Due to the many design uncertainties involved in the long term fatigue loading and performance of offshore structural components, in-service non-destructive inspections (NDI) are usually incorporated as part of the maintenance programme to ensure the actual performance abides. by the design. However, the (un)reliability of NDI introduces another type of uncertainty into the assessment process. The aerospace and other industries, facing similar problems, carried out extensive studies in NDI reliability and statistical trials.

The differences in the structural configurations, and in the operational features mean that data exchange between industries are difficult. However, the exchange of modelling and analytical techniques is possible.

This paper briefly reviews the development of the fitness for purpose philosophy in structural maintenance and the associated research in NDI reliability. Emphasis, however, will be put on the scope of applications in offshore structures. Moreover, the paper will discuss some problems which are unique to the offshore industry and these require special considerations in obtaining and using the NDI reliability data. Some possible solutions to the above problems will also be discussed in this paper and illustrated with examples.

Keywords

Fatigue Crack Growth Crack Size Structural Reliability Maintenance Strategy Offshore Structure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

A, B

Weibull distribution parameters

\(\hat B\)

Bias factor for σ

Cj

Paris crack growth constants for segment j

\(\hat K\)t

Non-dimensionalised stress concentration factor

P(X)

Structural reliability (probability of failure) before updating

P(XIθ)

Updated structural reliability (probability of failure)

P(θ)

NDI reliability (probability of sizing /detecting defect present)

a, a’

An arbitrary crack size

ai,af

Initial and final crack growth sizes

acr

Critical crack size (Maximum size prior to failure)

aNDi

Critical non destructive inspection size

â

A measured crack size

da/dN

Crack growth rate

fy(X)

Probability density function of Y when Y = X

g

State function

mj

Paris crack growth exponents for segment j

p(a)

Probability density function of crack size a

p(XIθ)

Probability density function of X given an event θ

ΔK

Stress intensity range

Ф(X)

Cumulative standard Normal distribution at X

β

Reliability index

δa

An arbitrary, infinitesimally small crack size

µx

Mean of X

σ

Long term stress time history root mean square (RMS) value

σx

Standard deviation of X

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References

  1. 1.
    Marshall, P.W.: “Problems in Long Life Fatigue Assessment for Fixed Offshore Structures”, Preprint 2638, ASCE, National Water Resources and Ocean Engineering Convention, San Diego, California, Apr., 1976.Google Scholar
  2. 2.
    Cohesive Programme of Research and Development into the Fatigue of Offshore Structures. July 1985 - June 1987. Final Report ed. by Dover W.D., Dharmavasan, S., UCL, 1989.Google Scholar
  3. 3.
    Kam, J.C.P. 1988: “Fitness for Purpose Assessment of Tubular Welded Joints in Offshore Structures”, Proc. 7th Int. Offshore Mechanics and Arctic Eng. Sym., ASME, Houston, Feb., 1988.Google Scholar
  4. 4.
    Kirkemo, F.: “Applications of Probabilistic Fracture Mechanics to Offshore Structures”, Applied Mechanics Reviews Vol 41, No. 2, Feb., 1988.Google Scholar
  5. 5.
    Rummel W.D., 1988.“Methodology for Analysis and Characterization of Non-Destructive Inspection Capability Data”, Review of Progress in Quantitative NDE, Vo17, 1988.Google Scholar
  6. 6.
    Madsen, H.O., Krenk, S., Lind, N.C.:Methods of Structural Safetv.Published by Prentice - Hall Inc.,1986.Google Scholar
  7. 7.
    Thoft-Christensen, P., Baker, M.J.: Structural Reliability Theory and its ApplicationsPublished by Spring Verlag, 1982Google Scholar
  8. 8.
    Hasofer, A.M., Lind, N.C.: “An Exact and Invariant First Order Reliability Format”, Proc. ASCE. Jnl. Eng. Mechanics Div 1974, pp 111–121.Google Scholar
  9. 9.
    Shooman, M.L.: Probabilistic Reliabili v: An Engineering Approach McGraw - Hill Book Co., New York, 1968.Google Scholar
  10. 10.
    Baker, M.J., Private communication on fatigue reliability of offshore structures.Google Scholar
  11. 11.
    Kam, J.C.P.: “A Study on the NDI and Corrosion Fatigue Crack Growth in Tubular Welded Joints Using Reliability Methodologies”, Proc. 9th Int. Conf. Offshore Mechanics and Arctic Engineering, ASME, Houston, 1990.Google Scholar
  12. 12.
    Department of Energy: Background Notes to the New Fatigue Design Guidance for Steel Welded Joints in Offshore Structures HMSO, London, 1983.Google Scholar
  13. 13.
    Kam, J.C.P., Dover, W.D.: “Corrosion Fatigue of Welded Tubular Joints: Fracture Mechanics Modelling and Data Interpretation”, Proc. 8th Int. Offshore Mechanics and Arctic Eng. Sym., ASME, The Hague, Apr, 1989.Google Scholar
  14. 14.
    Nichols, R.W.: Non-Destructive Examination In Relation to Structural Integrity (PISC-I) Applied Science Publishers, 1984.Google Scholar
  15. 15.
    Rummel, W.D., et al., 1974.Detection of Fatigue Cracks by Non-Destructive Testing Methods NASA Contractor Report, NASA-CR-2369, Feb 1974.Google Scholar
  16. 16.
    Forli, O.:A Comparison of Radiographic and Ultrasonic NDE The Danish Welding Institute, 1983.Google Scholar
  17. 17.
    Ledermann, W., 1984. Nand-book of Applicable Mathematics. Vol VI., Statistics. Part B Published by John Wiley & Sons, 1984.Google Scholar
  18. 18.
    Kam, J.C.P.: “The Efficient Maintenance of Offshore Structural Integrity Using Reliability Analysis”,Quality and Reliability Eng.Int. Jnl, Vol 5, No. 3,1989.Google Scholar
  19. 19.
    Wirsching, P.H., Chen, Y.N.: “Considerations of Probability Based Fatigue Design for Marine Structures”, Int, Jnl. Marine Structures. Design. Construction & S afetyv. Elsevier Applied Science, Vol 1, No. 1.Google Scholar
  20. 20.
    Bertini, L.: Private Communication on the Corrosion Fatigue Crack Growth Data Base University of Pisa, Italy, 1988.Google Scholar
  21. 21.
    Buchan, A. Comparison Between the Parametric Equations in Calculating Spot Stresses, Working Group Report for Fatigue Crack Growth Software (FACTS), Sept, 1989, Cohesive Programme of Research and Development into Fatigue Crack Growth of Offshore Structure, 1987–89.Google Scholar

Copyright information

© Elsevier Science Publishers Ltd 1990

Authors and Affiliations

  • J. C. P. Kam
    • 1
  1. 1.Department Of Mechanical EngineeringUniversity College LondonLondonUK

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