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The ABS-classed FPSO Cossack Pioneer started life as a 250,000 dwt very large crude carrier (VLCC), delivered in 1972. Substantially modified and converted to its current role in 1995 the vessel will undergo its seventh special survey in 2009 and its operator, Woodside Petroleum, is now working with ABS to identify the most effective way to extend the unit’s operating life.

In many cases, FPSOs are on-site for upwards of 20 years. In the case of the Cossack Pioneer it has been on-site for 12 years. With this extended time on station careful attention needs to be paid to the overall hull girder strength, corrosion and fatigue. 

For the Cossack Pioneer, ABS surveyors will provide survey assessments and conduct a series of close up survey inspections. Gaugings will also be taken in order to make life extension recommendations. ABS engineers will run fatigue analyses on the vessel for its field location offshore Northwest Australia.

SafeHull for FPSOs is a tool available from ABS that is used to evaluate the residual strength of a hull structure to determine its fatigue life. Hull fatigue life predictions can be updated continuously throughout the vessel’s lifetime. 

Related to this topic read the Offshore Technology Conference (OTC) technical paper from ABS Flexible Approaches to Risk-Based Inspection of FPSOs that discusses the challenges of how to efficiently manage the lifecycle integrity of an FPSO using a risk and reliability approach. The paper outlines a multi-level risk-based inspection methodology ranging from simplified deterministic approaches using standard design analysis to sophisticated probabilistic approaches.