Many North Sea installations are now at or beyond their original design lives, and this raises questions about the demonstration of the safety of the structures to remain in service. Whereas most of the topsides equipment is accessible for inspection and maintenance, and deteriorating parts can be repaired and replaced, such IRM is extremely expensive for the underwater structure. Indeed, widespread inspection of structures cannot realistically be undertaken for both cost and safety reasons. The North Sea concerns on managing life extension affect both fixed platforms and semi-submersibles, and these are also reflected in many other parts of the world including the Gulf of Mexico and the Far East.

The management of life extension requires an assessment of both the original design requirements, changes in standards and loading conditions and the current state of the structure. ISO 19902 includes a new section on reassessment, which has been developed with international input (including the authors).

A methodology has been developed by Cranfield University, in conjunction with Galbraith Consulting and Sauf Consulting, to assess how well operators and their contractors apply their knowledge of individual structures, corporate requirements, behaviour of materials and worldwide experience in determining inspection and repair requirements for an individual structure.

The work was funded by the Norwegian Petroleum Safety Authority (PSA), as they needed a tool to provide a framework for their structural audits; however the methodology can be used by operators as a self assessment tool. An assessment determines the "maturity" of the operators’ decision making in a number of different areas — higher maturity requires greater understanding and investment in planning, but the resulting maintenance should be both cheaper and safer, particularly for life extension purposes.

The paper describes the main issues in managing life extension, including evolution and operation of the above methodology.

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