This paper presents a method which utilises the inspection history/in-service observations to measure and improve the accuracy of fatigue analysis method. The method is exemplified by using more than 4000 NDT (Non Destructive Testing) inspection results in the period 1972 to 1995, including 600 platform years in the North Sea. Cracks were detected in 438 joints, while 181 joints have been found to contain propagating cracks ('fatigue cracks'). Each joint contains one or more cracks. The observations of cracks are compared with theoretical predictions using a probabilistic fracture mechanics approach. The experience clearly demonstrates that the present tools for predicting fatigue crack growth give very uncertain but generally conservative estimates of the fatigue life. However, 1 to 3 percent of the components that have long fatigue life, have been observed to develop propagating cracks in a period, which is 20 years or less. For main structural and horizontal framing components the theory overpredicts the number of propagating cracks by a factor of approximately 3 while it predicts 70 to 80 percent of the propagating cracks observed.


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    Title :

    Comparison between observed and predicted characteristics of fatigue cracks in North Sea jackets


    Contributors:
    Vardal, O.T. (author) / Moan, T. (author) / Hellevig, N.C. (author)


    Publication date :

    1999


    Size :

    10 Seiten, 15 Quellen


    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English