Protective coating systems are applied to protect offshore structures against corrosion in the splash and atmospheric zones. Due to limited accessibility and high repair- and maintenance costs for coatings offshore, the protective coating systems for offshore wind turbines should aim to be maintenance free for the designed lifetime, typically 25 years. Constant wetting by seawater and limited effect of cathodic protection makes the splash zone particularly challenging with respect to corrosion protection. According to experience from offshore oil & gas industry lifetimes above 25 years are expected for thick-film epoxy and glass flake reinforced polyester in this zone. For 3-coat paint systems used as corrosion protection in the atmospheric zone, the lifetime is typically 10 years or less, i.e. coating maintenance has to start after 8-10 years. Offshore wind towers are often protected by duplex coating systems consisting of metallized zinc (TSZ) and a 3-coat paint system. Such duplex coatings are regarded as maintenance free even in harsh environments. The present work was initiated to reduce costs of protective coating systems for offshore wind structures. Duplex coatings with reduced paint thickness, reduced number of paint coats, paint modification, and reduced TSZ thickness are investigated. The coatings are tested with respect to ageing resistance according to ISO 20340 and in a 3.5 to 5 years field exposure test at Fraunhofer IWES' test station at Heligoland.
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