New developments in coatings for extended lifetime for offshore wind structures
After more than 15 years’ service life of the first large offshore wind farms in the North Sea, mostly positiveexperiences are reported on the condition of the protective coating systems.
Today however, the requirements for corrosion protection for new projects are often extended to at least 25 years’ maintenance-free service lifetime.
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Constructions such as offshore windfarms are subject to aggressive environments. They are exposed to humidity with high salinity and to intensive UV-radiation. The UV-radiation occurs directly on the constructions as well as from light reflections from the sea.
An area of special concern is the tidal zone (splash-zone), where the wind turbine construction is stressed both from mechanical impacts – service boat collisions and waves – and from corrosion strains created by shifting saline seawater with high oxygen level.
The stress from seawater may be extensive in waters with high tidal activity, such as the Irish Sea or the English Channel. Thus, in particular, the protection of the wind turbine foundation, the transition piece (TP), is imperative. Long-term resistant coating systems with no need for future refurbishment – combined with flawless application operation activities – are essential, as offshore repair is costly.
Following an uncertain start, the present offshore coating systems for windfarms have shown fine durability against the aggressive marine environment. Positive features from the first windfarms with more than 15 years of service are described. The importance of quality management, satisfactory coating performance testing and learnings from existing and decommissioned structures are explained in this paper.
After more than 15 years’ service life of the first large offshore wind farms in the North Sea, mostly positive experiences are reported on the condition of the protective coating systems.
In this paper experiences from site inspections of offshore wind farms in operation and from decommissioned constructions have been discussed. The trends seen in the offshore wind segment are requirements for corrosion protection being extended to at least 25 years’ maintenance-free service lifetime.
This fact is also reflected in newly issued and coming standards where extended prequalification tests (such as long-term field exposure for 5 years, abrasion, impact and color retention tests) are included in order to convince owners and certifiers that new coating systems may actually have 25 years’ maintenance-free service lifetime.
On the other hand, this paper also suggests that prequalification tests alone do not necessary pull out the right coating systems for real service. The lifetime of a coating system also highly depends on the quality of surface preparation, the coating thickness and the quality of workmanship. At the same time, these factors are usually the most uncertain elements and require strict QC during production.
One might think that the demand for extended service life and at the same time the wish for cost reductions point in opposite directions. This is not necessary the reality:
- More QC during the coating process will extend the service lifetime of the coating system and thereby also reduce the overall costs for corrosion protection.
- Learnings from extended pre-qualification tests go hand in hand with real life experiences from site inspections of constructions in operation and constructions being decommissioned. The experience from both scenarios will continuously help optimizing the coating systems needed for wind offshore service and help in updating standards and guidelines to make extendedservice lifetime for offshore wind structures possible.
- Novel concepts bringing in automated production processes and application of standard components might be tools to improve production quality and thereby extending the useful service life of the coating system, and at the same time bringing down production costs.