Abstract
This paper presents a case study of the development of a risk-based inspection plan as part of the structural integrity management (SIM) of eight fixed offshore structures in Brazil. Alternatively, to the consequence-based approach, a risk-based philosophy was adopted to optimize inspection efforts related to the SIM program of eight jackets in Brazil.
The procedure to select what to inspect and how to inspect was based on API-RP-2SIM and ISO 19901-9 standard. The procedure considered quantitative methods to evaluate the level of redundancy of the platforms under extreme storms, and a semi-quantitative method to classify the importance of each joint to the global integrity of the platform jacket. Firstly, the probability of failure by fatigue of each joint was assessed following DNV recommended practice. In sequence, depending on the structural importance of each joint, a reduction factor of the global reserve strength of the jacket was considered in case such joint would fail due to fatigue. Finally, it was possible to define the potential increase of jacket global collapse probability under hypothetical joint fatigue failure scenarios.
By combining the importance of each joint to the overall jacket strength and the fatigue probability of failure, it became possible to understand, on a life extension perspective, which joints represent significant global failure risk increase to the platform. The riskier joints could then be prioritized by the inspection program and the joints which were not increasing the risk of global failure could be disregarded. In addition, it was possible to differentiate the joints worth of GVI, CVI or NDT, depending on the risk level each joint represents to the safe operation within design life. The application of the proposed procedure to the selection of joints to be inspected for eight jacket structures in Brazil coast demonstrated that, conversely to the consequence-based inspection program, by adopting semi-quantitative and quantitative methods, it was possible to significantly reduce the inspection scope, while at the same time, not reducing the global failure risk of the platform.
The present study applied available software tools to better assess the risk of each joint with focus on the global strength of jacket structures, independently to the year this platform was designed, demonstrating that to inspect less joints does not necessarily mean running intolerable risk.
