Under the development of the Brazilian pre-salt onerous concession areas Petrobras contracted Enseada Industria Naval for the conversion of 4 (four) VLCC ships into the hulls of FPSOs P74, P75. P76 and P77, for which PROJEMAR have awarded a contract for the complete hull conversion engineering design.

Even with the accumulated experience on the design of 12 (twelve) FPSOs conversions, nothing could be compared with 4 (four) ships being simultaneously converted in two shipyards, being one in Brazil and one in China, to receive 4 (four) Process Plants weighting about 35.000 t designed by 3 (three) different Topsides engineering designers.

This paper intends to describe the main challenges and achievements of the engineering design work for the conversion design of the 4 (four) FPSOs, where the need to maximize standardization conflicted with the different hull configuration of the VLCCs that were being converted, with the different production characteristics of the two shipyards involved on the conversion work and with the different design philosophies of the Topsides engineering designers. These can be exemplified by:

  • The need to face single hull and double side VLCCs that were built in different shipyards in Korea and Japan, what led to different main deck reinforcement and different strategies for steel renew;

  • The different Topsides engineering led to different main deck reinforcements for the Topsides equipment and structures;

  • The main equipment was standardized, but the different ship´s hull structure led to different structural solutions, and smaller equipment were acquired from local suppliers close to shipyards;

  • Different arrangements and tanks configuration led to different piping designs;

  • A new standard accommodation block needed to be fitted in different main deck structure configurations;

  • Individual motions analyses were carried out for each FPSO, but needed to be validated by a unique model tests program;

  • etc

In summary, maximize the design standardization is a key path to improve construction productivity, but as an FPSO conversion design is essentially a tailor made activity, this duality was highly pronounced when dealing with the multiple simultaneous activities of the Cessão Onerosa FPSOs design.

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