RELIABILITY BASED INSPECTION PLANNING OF A JACK-UP RIG

A reliability based inspection planning of the spud-can-chord connections in a jack-up structure were performed as these have shown to be prone to fatigue cracking. A non-linear dynamic stress range distributions is established and the effect of non-linearity in the inspection planning is thereby included. The non-linearities and dynamic amplifications of the wave loads are determined in the stochastic seaway by a consistent procedure, based on the theory of diffusion processes. The dynamic stress range is multiplied by a correction factor, derived from finite element calculations and measurements, to obtain the hot-spot stress range needed in the fatigue calculations. The fatigue crack growth is calculated for a two- dimensional semi-elliptical surface crack, and used for the reliability based inspection procedure to obtain suitable inspection times. A numerical example illustrates the procedure.