Offshore Floating Units, usually deployed under long-term plan, handle the field production so they cannot be easily removed for dry-docking and repair. An Asset Integrity Management System (AIMS) has been developed for several major complex Floating Units currently in operation for TOTAL.
This paper focuses on the methodology developed for two significant units: the concrete N'KOSSA FPU located offshore Congo and the huge GIRASSOL FPSO installed offshore Angola. The FPU is the largest pre-stressed concrete floating production unit built with high performance concrete, installed offshore since 1996 in 170 m water depth. She has now accumulated almost 10 years of production. The GIRASSOL FPSO was installed offshore Angola in 2001 at 1,400 m water depth. The experience gained from this particular FPSO is also very important, considering the challenges this unit raised.
The paper describes the various results obtained. In particular: For the concrete unit, a significant part of the methodology is based on a full finite element model with non-linear analysis capacity for the concrete structure, incorporating a description of passive and active steel. The model has been calibrated by comparison with the design and the concrete characteristics used during the construction, allowing in the same time a verification of the design of the structure. This model is coupled with the inspections carried on board providing, with time, a closer understanding of the floating unit structural behavior.
For the GIRASSOL FPSO a coupled structural model is developed incorporating the interaction of the living quarters and the topsides with the main hull. In particular this model will be used to analyze accurately the effect of additional topsides during the Rosa field hook-up in 2006. A global dynamic model has been developed as well to describe the interaction of the FPSO and the offloading buoy connected by underwater transfer lines, and the behavior of an export tanker in tandem offloading. This model allows the calculation of the residual fatigue life of the moorings.
The Asset Integrity Management System is a multidisciplinary coordination tool. It is a living system that will continue to develop and mature with time and use. It will improve information and documentation transfer. But more important it will help in minimizing production shutdown and optimizing maintenance and repair costs.
Following TOTAL Corporate Requirements , a Floating Unit Integrity Management program is to be implemented to ensure management and continuous follow up of all floating units from a safety, environmental, operational, maintenance and quality management viewpoint. It includes recommendations on inspection, maintenance and repairs. The main activities called in this Program are the following:
Structural and mooring analysis
Qualitative RBI implementation
Yearly review of the IRM plan
Data management and storage
Assistance for Emergency First Response.
These requirements are applied to F(P)SO Units in general, although differences between the various types of units will impose a case by case study to know which services and systems are the most appropriate to each Floating Unit.