Influences of Seawater Flows on the Degradation of Organic Coatings Applied on Offshore Wind Turbines
Abstract
The regular protection methods of offshore wind structures consist of the application of two or three layers of epoxy-based coatings with a polyurethane topcoat. The coating systems of offshore wind turbines are mostly tested on-site, where different coated samples are exposed to the sea water at the specific locations planned for the installations of the turbines. Despite several advantages of laboratory testing, the majority of laboratory-based tests have been limited to the exposure of coated or unprotected metals to stationary electrolytic solutions, while the flow-induced corrosion measurements have not received enough attention until recently. The focus of our work is to investigate the influence of applied mechanical stresses due to the water flow on the degradation of organic coatings. In order to resemble the condition of coated monopile structures in shallow water flow, an impingement chamber device and a wave tank were designed and constructed. The Electrochemical Impedance Stereoscopy (EIS) method was utilized for monitoring the electrochemical processes occurred during the degradation of coatings. Computational Fluid Dynamic (CFD) method, as well as Particle Image Velocimetry (PIV) tests were utilized in order to calculate the magnitude of applied stresses on the coating surfaces. Atomic Force Microscopy method (AFM) was employed for characterizations of coating’ surfaces. The theory of thermo-activated processes in combination with the thermoelasticity equations were derived in a way to calculate the influence of applied stresses on different electrochemical parameters of the coatings’ degradation. The afore-mentioned experimental methods and the developed analytical procedure can potentially predict the behavior of organic coatings applied on offshore wind turbines at different exposure zones with respect to the sea water flow.