The majority of offshore installations worldwide are currently operating beyond their design life. There are still plenty of oil reserves left in existing fields and new smaller fields are unprofitable for stand-alone development. It is therefore essential to use the existing infrastructure efficiently. There is a need to estimate the remaining life of ageing installations more precisely. Ageing is generally characterized by fatigue and corrosion. For an accurate estimation of the remaining life, it is important to simulate the past loadings and structural degradation precisely. However, the past loading histories are generally not available. Also, very few guidelines are available for the simulation of structural degradation in the absence of thickness reduction measurements. To address these issues, this paper first presents an overview of the age profile of fixed offshore installations. The simulation of past loading and structural degradation is then discussed. Guidance is provided on the selection of a suitable wave scatter diagram to represent past loading precisely. Guidelines are also provided on the selection of suitable corrosion wastage model parameters especially in cases where detailed degradation data is not available. The significance of the proposed guidelines is highlighted through a case study on an existing ageing jacket structure. Finally, conclusions are drawn and recommendations are made.

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