Recovery of an elevated jack-up with leg bracing member damage

Source Information
May 2004, Volume17(Issue3-4) Page325To351

During the winter of 2001-2002, while drilling over the Leman Delta platform in the southern North Sea, a modern harsh-environment jack-up operating in shallow water on a hard sandy bottom encountered an incrementally increasing, partly scour-induced, problem with eccentric spudcan loading and associated rack phase difference (RPD). After 3 months on location, while the unit was in the process of being re-levelled for the third time, leg braces were damaged. The decision was taken to move the jack-up to a shipyard to repair the damage, and this paper describes the analytical and practical steps that were taken to do so in the least hazardous manner. The mechanics of the RPD effect are described in detail, and the observed bracing damage is assessed against the theoretical models that were used to predict behaviour. Some general conclusions on the best methods of handling units suffering this type of damage are drawn, and suggestions are made on how to minimise similar damage in the future.

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doi: 10.1016/j.marstruc.2004.08.007