As with many other offshore structures the primary corrosion control method is the coating applied to the hull, this is backed up by a cathodic protection system that takes care of exposed steel at coating defects. When designing the C.P. system, it is necessary to predict the efficiency of the coating system both initially and at the end of life. Given that regular ocean-going vessels are required to be dry-docked at intervals not exceeding 5 years, there is always an opportunity to repair or re-coat the hull during the ships life, thus the coating degradation has only to be considered over this time span. An FPSO on the other hand may be offshore for 15+ years. This will require a re-evaluation of the coating performance at the end of this period and appropriate re-sizing of the cathodic protection system current capacity to deal with the increased bare steel area.
Special attention must be paid to the compatibility of the coating system with cathodic protection, this is particularly true of impressed current systems that will generate higher negative potential values at the edges of the dielectric shields associated with hull mounted anodes.
See also: Fouling,FPSO, Ions in seawater,DO in seawater, Seawater scaling, Anti-fouling coatings