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8738309 
Meetings & Symposia 
Lessons learnt from 12 years of operations of a huge floating production unit made of pre-stressed high performance concrete 
Lanquetin, B; Dendani, H; Collet, P; Esteve, J 
2008 
3 
1966-1980 
English 
The last years have seen an impressive increase of Floating Production Storage and Offloading (FPSO) units deployed all over the world both in number and in variety of designs. But all of them in steel.This paper presents the lessons learned from the huge floating production unit made of pre-stressed high performance concrete in operation for TOTAL E&P Congo.They touch all aspects of the life of the unit, design, construction and maintenance on site. The paper will also present the main key issues for the floating concrete structures and some guidelines on how to avoid them, resting on some of the available existing codes.The unit is in production since 12 years on the N'KOSSA oil field in 170 m water depth. Main characteristics: L 220 m, B 46 m, D 16 m, displacement 107,000 t including 73,000 t for the hull and 34,000 t for the topsides. This concrete unit used for construction 27,000 m3 concrete, 2,3501 pre-stressed steel and 5,0001 passive steel.This paper focuses on the following aspects specific to this floating production unit:Structural modeling techniques taking into account the non-linear characteristics of concrete and incorporating a description of passive and active steel. Ageing processes of the concrete units and the general typology of the defects encountered.Development of a tailor-made inspection program. Pre-stress concrete has many virtues and the fabrication process gets more and more industrialized, with better knowledge of the parameters and how controlling them. This makes it a potential material candidate that can allow new-builds outside traditional shipyards, providing new opportunities.However the paper is not intended to make a recommendation between steel and concrete because this entails many other considerations that are not only technical; the paper remains on the technical ground and shares valuable knowledge on the behavior of floating concrete units on the long term prospective of a field life time and on the integrity management techniques developed the minimize the risk of production shutdown and optimize maintenance and repair costs. Copyright 2008. International Petroleum Technology Conference.