Reassessment of installations on the UK Continental Shelf is an important control measure in assuring continuing structural integrity. At present this is achieved via the certification process. Risk based regulations have now been introduced requiring a safety case for each installation; these will be supported by the introduction of additional regulations. Preparation of the safety case requires the identification of major accidental hazards and a demonstration of how the associated risks are to be controlled. In the US reassessment procedures have been developed and issued in 1993 as draft section of API RP2A. Structures installed some time ago have been designed to codes and standards, for which the design requirements may have since changed as a result of more data becoming available. Examples are given for both the static and fatigue strength of tubular joints. Other important factors include the design wave height and the air gap: System behaviour and reserve strength are important in justifying performance and an acceptance criterion for reserve strength is included in the draft section 17. Recent HSE studies on benchmarking "pushover" type software have shown that current industry practice can lead to significant variations in prediction of reserve strength. In addition consideration of reserve strength alone may not be sufficient to demonstrate the adequacy of reserve capacity in a structure.
There is a need to provide adequate structural integrity of North Sea installations as an important contribution to the overall safety of the workforce that use or visit such installations. An increasing number of offshore installations are approaching the end of their original planned life and decisions regarding their ongoing integrity for future operations are required. One part of this decision making process is the role of re-assessment as a control measure in assuring this integrity.