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RR429 - Structural Reliability Framework for floating production, storage and offloading vessels/floating surface units Phase II

Structural Reliability Analysis (SRA) is a tool for calculating failure probabilities of a structure that takes into account all random variables involved in ship structural design and provides a better and alternative to deterministic approaches. With a number of different regulations based on structural reliability theory already existing for some time now in the areas of Civil and Aeronautical engineering and the Nuclear Power industry it has been only a matter of time before the ship/offshore field implemented such a procedure into its regulatory regime. Classification Societies have published since the early 1990s suggestions of how reliability analysis techniques can be used to analyse structures and recently some have incorporated and accepted those as an equivalent means of analyzing structures to supplement their existing regulations.

This research examines the structural reliability of Floating Production, Storage and Offloading Vessels (FSPSO)/Tanker structures already in operation in the North Sea/West of Shetland area, using a component time-variant reliability approach that takes into account the most suitable approach for calculating the ultimate strength of the vessel’s structure. Corrosion effects on the structure are modelled using a non-linear mathematical model based on actual measurements. Emphasis is placed on the modelling of loads for use in reliability analysis. Load combination methodology is used for the combination of wave bending, still water, slamming and thermal loads using a variety of different approaches. FPSO/Tanker vessels are analysed using First and Second Order Reliability Method (FORM/SORM) but also time-variant Monte Carlo simulation component reliability techniques to obtain Partial Safety Factors and probabilities of failure.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2010-03-19