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The use of floating production, storage and offloading (FPSOs) vessels has rapidly increased in recent years. The advantage of FPSOs over other floating production facilities is the ability to store produced fluids, which can be later offloaded to a shuttle tanker. The components of an FPSO include the vessel (which is either a new build or a tanker conversion), the mooring system, the processing facilities, and the storage tanks. A riser system is usually attached to the FPSO to permit produced fluids from subsea fields to be processed on the topsides equipment. FPSOs differ from mobile ships in that they are positioned in a stationary condition over the production field for years at a time.
An FPSO is a complex structure when it comes to corrosion control. Numerous types of coatings are utilized to protect surfaces from corrosion. Cathodic protection is included to protect the external hull from corrosion caused by the seawater. Cathodic protection is also applied to the internals of many tanks that can contain water such as ballast, slop, and cargo tanks. This article will focus primarily on the coating requirements at the new build stage for the FPSO hull, ballast tanks, cargo tanks, and topsides equipment. This article is not intended to be a comprehensive discussion of all companies' FPSO painting practices but is an overview based on those of the authors' company and their knowledge of common industry practice.
Method of Corrosion Protection for FPSO Hulls
Generally, the preferred form of corrosion control for an FPSO hull exposed to seawater is a combination of coatings and cathodic protection. The offshore industry has long-term experience selecting and applying hull coatings. Typically, the hull coating system includes various layers of epoxy paint. The epoxy needs to be compatible with the preconstruction primer (PCP) normally applied during hull plate fabrication. Often, an antifouling topcoat is used. Not all operators use an antifouling paint because its performance in eliminating fouling under static conditions is not well documented and proven. However, it is commonly accepted that the antifouling paint may not fully eliminate all marine fouling but will assist with underwater hull inspection by allowing easier fouling removal.
Finally, the hull coating system needs to be compatible with the cathodic protection system. Typically, a cathodic...