Key parameters and guidelines for achieving a corrosion protection system for newbuilding FPSOs have been established by DNV. If used properly, operators’ costs over the lifetime can be reduced significantly.
The number of Floating Production Storage and Offloading (FPSO) vessels actually operating around the world has increased to more than 100. Up to now, a cost-optimal corrosion protection system for these and coming vessels has not been in place.
Many of the current newbuilding FPSOs are being built to function on huge oil fields and some have production capacities in excess of 200,000 bbl per day. Any lost production time can have very significant economic consequences.
The new corrosion control design addresses both the fabrication of a new vessel and the operational aspects of a producing unit.
For a newbuilding FPSO, corrosion management involves decisions taken at various stages relating to design, fabrication and operation. A combination of specific corrosion margins, coating systems and cathodic protection systems is recommended in the new guidelines.
During the operational phase, there are some factors that tend to significantly influence the corrosion wastage. These include temperature increases, oxygen in seawater, chlorinity, humidity, temperature gradients and types of cargo oil. The relative impact on corrosion protection design is indicated in the guidelines. A cost optimal inspection, maintenance and repair system intended for a 20-year service life remains a major challenge. Consistent inspection plans for all essential areas, based on all relevant design parameters and guidelines for the coated surfaces, can then be achieved.
Corrosion can result in fatigue, buckling and leakage, and leakage can again lead to pollution and, in the worst case, explosion. Therefore, it is very important to design, implement and manage a proper corrosion protection design.
DNV’s recently developed tool (CoatInsp) for the cost optimised planning and follow-up of coating systems over the lifetime is also presented in the guideline.