Assessment of Existing Offshore Platforms

The subject of this work is the evaluation of possible life extension of existing offshore jacket structures. The relevant standards for life extension of existing offshore jacket structures as reviewed, with focus on ultimate limit state analysis and fatigue analysis. In general , it can be said that the existing standards and procedures recommend assessment of existing structures for life extension based on linear analysis and component checks, non-linear system strength analysis and component checks and structural reliability analysis for the ultimate limit state check. A risk evaluation of an ageing structure in needed as a part of the assessment . such a risk evaluation should include identification of hazards and failure modes. A review of hazards and failure modes for an ageing offshore jacket structure are presented. It is concluded that a review of hazards and failure modes should be included as a part of an assessment for life extension. It is chosen to represent the system strength with the reserve strength ratio indicator and damage strength with the damaged strength ratio. The use of different probabilistic methods in assessment for life extension is also evaluated. It is focused on a predictive Bayesian approach for probabilistic assessment.