Observations made during more than 4000 in-service nondestructive examinations of tubular joints in North Sea jackets are utilized to determine the initial crack depth and probability of detecting (POD) cracks in magnet particle and eddy current inspections. Based on exponential distributions of the initial crack size and POD, it was found that the mean initial crack size and detectable crack depth was 0.94 and 1.95 mm, respectively. This initial crack size is referred to one crack occurrence per three joints and corresponds to a mean crack depth of 0.38 mm with a frequency of one crack per hot-spot area. The predicted number and size of undetected cracks are found to correspond well with actually reported “second inspection” cracks. The estimated depth of undetected cracks is used to estimate how deep the post-inspection grinding should be, to establish a certain residual fatigue life. [S0892-7219(00)00503-3]

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