Detailed Fatigue Analysis for Jackets in Shallow Waters of Bohai Bay

摘要

Because in shallow water it is uncommon for jacket platforms to have fatigue problems, the simplified fatigue analysis can be used instead of detailed fatigue analysis under some conditions which have been defined in many related international standards, for example API. However, according to the results of detailed fatigue analysis for shallow water jackets with relatively large natural period, we find that the fatigue life of some joints may not satisfy the design requirements even though they can satisfy the simplified fatigue analysis conditions. In order to make clear the reason, in this paper some design properties of these jackets are discussed such as design water depth, natural vibration period, conditions for simplified fatigue analysis and yearly probability of wave occurrence. Finally we find that when the natural vibration period of these jackets is close to the wave period, resonance which can cause fatigue problem of tubular joints usually occurs between the jackets and wave. So if you don't have enough confidence, detailed fatigue analysis should not be replaced, although these replacements may accord with some international standard.