Reliability Based Assessment for Fatigue Integrity Management

Reliability analysis can be used to assess the risk of structural failure in ageing offshore installations and to subsequently optimise inspection plans. This paper describes the findings of a joint industry project to develop and implement a methodology for system reliability updating based on the results of in-service inspections. The effects of different combinations of inspection techniques, namely flooded member detection (FMD) and magnetic particle inspection (MPI), and inspection intervals on the component reliability were examined. Additionally, a case study was performed to demonstrate the system reliability of actual structures with inspection histories. A comprehensive methodology for updating the assessment of system reliability of offshore structures based on in-service inspection results was developed. The methodology allows several important features associated with system reliability, i.e. redundancy, stress redistribution and correlation between the random variables, to be accounted for. The structural reliability is given in terms of an overall reliability for combined fatigue and pushover. The study demonstrated that the methodology may be used to target inspections to those areas of the structure with low fatigue life and low redundancy.