The efficient maintenance of offshore structural integrity using reliability analysis

Abstract

AbstractEfficient maintenance of offshore structures is one of the priority development areas of the offshore industry world‐wide. The maintenance of the installations in a hostile environment such as the North Sea poses a particular problem. Owing to the large number of wave‐induced stress cycles experienced by the structures, the integrity is subject to progressive degradation under fatigue crack growth. If cracks are discovered in service, the operators of the structures will need to decide on the appropriate course of action. The priorities for actions will also need to be determined for cracks of various sizes found in different locations of the structures.In the past, the above decisions have depended very much on engineering judgement. However, the latest developments in reliability fracture mechanics (RFM) analysis have for the first time provided an objective criterion for this type of decision making. Moreover, this criterion is consistent with the established structural design criteria based on reliability analysis of strength—load interaction. Therefore, it has become a real possibility to incorporate structural integrity considerations by design.The reliability‐fracture‐mechanics‐based fatigue analysis includes studies on the uncertainties of load history, materials crack growth behaviour, fracture mechanics modelling, non‐destructive inspection and other environmental factors. This paper will review the development in this methodology.In order to integrate the above analysis into the overall design process, it is useful to carry out reliability analysis for the complete structural system. The current state of the art of structural system reliability analysis is therefore briefly reviewed. The necessary development in order to accommodate fatigue reliability degradation is then discussed.