On assessment of existing offshore structures

The methods normally used for assessment of existing offshore structures are based on design level check, ultimate strength check or on a probabilistic approach. There are arguments against all these methods. Design level analysis are claimed to be very conservative, as after some years of experience the knowledge of the structure are increased compared with design. Ultimate strength analysis are claimed to cover only a small part of the hazards that should be analysed. The probabilistic approach is claimed to be model dependent and to give inconsistent results between analysis groups, as the subjective choices of the analyst are of significant importance. It is also claimed that there is no reasonable target reliability in a reliability approach, but that this has to be established in each case dependant on the methods and models that are used. The probabilistic approach is tending towards a Risk approach, but is claimed to not fully appreciate all the possible hazards for an offshore structure. This paper describes procedures for safety assessment of existing offshore structures as described in ISO 13819-1 (ISO 1995), API RP2A-WSD (API 2001), ISO/DIS 13822 (ISO 2000) and ISO/CD19902 (ISO 2001). The procedures are presented and discussed as how they are capable of being measured against a goal of even and acceptable risk for the society.