Corrosion Protection of Wind Turbine Support Structures
There are three distinct areas of the support structure which usually consists of a monopod and tower that require protection,
- Atmospheric Area -The area above the Splash Zone which includes the turbine tower
- The submerged area
- The Splash Zone
This area is above the splash zone and includes the turbine tower.
It is normally protected by the following applications,
1. Zinc primer applied preferably as a thermal spray
2. A silicon epoxy resin sealant
3. A coating of two-part liquid epoxy coating
4. A final coat consisting of polyurethane which consist of one or two- part and applied by brush or spray and are normally moisture curing and drying if solvent free.
The submerged area (Monopod Type)
This can be protected by the application of a coating of two-part epoxy compound, being applied at the construction yard.
A method of cathodic protection using zinc anodes should also be used to compliment the epoxy coating.
The anodes can be either fitted at the construction phase or an underwater sledge arrangement used. Both methods have their merits, the onshore fixing of the anodes to the structure being quicker and more economical, but difficult to replace under water.
An underwater sledge consists of a frame which contains numerous anodes welded into it. The frame is then positioned close to the support on the seabed and connected to the structure by heavy copper wire cables. This method allows for easy replacement of anodes but is expensive due to its installation to the location and, connection to the structure which requires underwater welding by divers.
Splash Zone Protection
This area requires treatment due to its contact with the seawater combined with the salt-laden air of the marine environment.
The offshore oil and gas industry has historically used rubber coatings or aluminium spray as a corrosion protection method. However, because of the simple structure design of a monopod, compared to the intricate oil and gas platform steel jacket supports, it doesn’t really warrant these expensive applications.
It can be adequately protected by using an identical anticorrosion procedure as that of the atmospheric area. Alternately a relatively new concept in corrosion attack is to apply two layers of polyester based powder which should attain at least a 1000um thick coating.