Performance and integrity of protective coating systems for offshore wind power structures after three years under offshore site conditions

Abstract

Six corrosion protection systems for offshore wind power constructions have been subjected to offshore conditions on a test site in the North Sea in three different exposure zones, namely splash zone, intermediate zone, and underwater zone. The systems included single- and multiple-layered organic coatings, metal-spray coatings, and duplex coatings. Special testing specimens were designed and manufactured and exposed to an offshore environment for three years in order to characterize particular constructive details for different corrosivity zones. The following target parameters were investigated: intensity of fouling, anti-corrosive effect, coating adhesion, coating integrity, flange corrosion, coating performance over welds, and condition of screw connections. Fouling was an issue in the underwater zone and in the intermediate zone, but it did not affect the coating corrosion protection capacity. It was found that duplex systems, consisting of Zn/Al spray metallization, intermediate particle-reinforced epoxy coating, and polyurethane top layer, provided the highest anti-corrosive effect. Mechanical damage to the coatings initiated coating delamination and substrate corrosion. Effective coating systems should be either very resistant to impact or able to compensate for corrosion of the steel. Flange connections were found to be critical structural parts in the splash zone in terms of corrosion. Notable crevice corrosion was observed at places. Except for one coating system, welds have been protected well. Welds, however, affected the corrosion of the steel inside the uncoated internal sections in the underwater samples. Coating integrity on difficult-to-coat structural parts was satisfactory for all systems.