Publications

Most people agree on the necessity to carry out numerical analyses on converted units to evaluate their adequacy for the future offshore service and the latter analyses are usually required by Classification Societies for Certification purposes. For new-builts, Class Rules exist that define the calculations needed for the design evaluation. For some time now the use of Offshore Floating Units has been increasing steadily and the prospects are that it will continue growing in the next couple of years. FPSO’s (Floating Processing Storage and Offloading), FPU’s (Floating Processing Unit) and FSO’s (Floating Storage and Offloading) seem to have the stronger growth rate, be it new-builds or conversions. The latter are always an attractive option as they may reduce times for deployment and CAPEX. The converted vessels are usually “mature” VLCC`s (being 20 years old or more) and may have hidden defects and weaknesses not always evident through inspection. A standard design approach on the converted unit can leave unattended many potential flaws that would otherwise be spotted if the previous service life is taken into account. The benefits of an early and thorough analysis to the conversion inspections are long-termed. Being FPSO’s complex systems where production rates are always threatened by several degradation mechanisms implicit to the process, the addition of a hurdle which is the flaws of the supporting hull structure can delay the expected payback time. Apart from being economically annoying these flaws can lead to sea pollution and if not treated correctly, place the whole asset in danger. The hull is not the expensive part of a deep-water production project and the expenditure and time needed to assess conveniently the state of the structure is nothing compared to the possibility of having to reduce by half the production rate and storage capacity because cracks have appeared on several tanks. A huge investment is made on the topsides and subsea equipment which may have to stay idle because not enough thought was given to the sustaining structure. Similarly, the new oil and gas recovery solutions and the current oil prices have led to economic development of marginal fields or extended exploitation of existing ones beyond the original expected life. This leads to keeping the assets for a longer period thus requiring a life extension assessment. This paper will present the available analysis that can define the structural needs for a safe operation and the state-of-the-art on conversion or life extension. Examples of typical concerns that have been reported in converted units will be given.