The FPSO's now under operation or construction are mainly ship-shaped structures. However these units differ significantly from oil trading tankers for their service conditions, being in continuous operation at sea and Site specific as opposed to ocean trading. Therefore, Classification Rules for FPSO's are providing complement, and provide the necessary input, before application of the Ship Rules that are the standard reference for shipyards.

A FPSO is constantly in loading/unloading process and loading conditions have to be carefully studied, taking into account both operating requirements, and future maintenance and inspection requirements.

As a FPSO is a site specific unit, study of the loads induced by waves is to be performed, and comparison of the results with the standard requirements for trading ship will provide the data required for the application of (ship) Class Rules.

Given Operator's objectives of a vessel in continuous operation at sea, and no dry-docking for the intended service life, durability is an essential consideration, with implication on design for e.g. accessibility, corrosion protection and corrosion margins, and Fatigue strength.

Tools are available, at the design stage, to perform strength and fatigue evaluations of the structure, and help in design. The database thus obtained will provide, during vessel operation, a compliance management tool for the hull structure.

Issues in this paper are discussed based on the experience gained in new-built but also converted FPSO's actually moored in various areas of the globe like West Africa, China and Brazil.


The FPSO's (Floating Production Storage and Offloading Units) now under operation or construction worldwide are mainly ship-shaped structures purpose-built or converted by shipyards based on their know-how and application of Classification Societies Rules.

The Classification Societies were established during the 19th century with the development of the shipping industry, to provide independent information on the actual condition of the ships, and to develop Rules for Classification of Ships including design, construction and maintenance/surveys requirements.

With the development of international conventions, Flag states have recognized their competence and technical expertise and have often delegated their technical inspections to them.

This has helped Classification Societies to harvest and compile unrivalled knowledge in terms of ocean-going structures and safety at sea. Then, the development of an expertise in offshore installations was considered as a natural extension of their duty of encouraging the protection of life and environment at sea.

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