Offshore wind turbines are considered as a reliable source of electricity generation. However, due to the large cost of the construction, installation and maintenance of offshore wind turbines, most offshore wind turbines are designed to operate for more than 20 years. One of the biggest issues which causes a severe damage to the construction of offshore wind turbines is the existence of a very corrosive environment including large mechanical loads applied to the construction by the waves, as well as the high concentration of salt and other chemicals in the sea water. The construction of offshore wind turbine can be divided into four main regions based on the types of exposure to the water and the corrosive environment, including submerged zone, tidal zone, splash zone, and atmospheric zone. Corrosion occurs due to bacterial growth, chemicals, PH level, and salt content of the water, while abrasive action of waves expedite the failure rate of the coatings. The corrosion rate at different zones varies due to the unbalanced participation of different corrosive factors in the degradation process. In this study, experiments were conducted to compare the impact of impingement flow of 3.5 w.t. %  NaCl solution on the epoxy coating samples to the exposure of the same type of samples to a stationary 3.5 w.t.% NaCl solution. Those two exposure conditions correspond to the environments at the top part and the bottom part of the submerged zone of offshore wind turbines respectively. Electrochemical Impedance Spectroscopy (EIS) method was used  to monitor the degradation of organic coatings. Equivalent circuit models are employed to interpret the EIS spectra. Atomic Force Microscopy (AFM) was employed to study the influence of fluid flow on the surface topology of the coating samples. The roughness of the coated surfaces before and after the exposure was compared. For the two different flow conditions, i.e. impingement flow and stationary immersion, significant differences have been discovered from the EIS results and AFM results. We observed a more severe degradation in the epoxy coatings in impingement flow, and a rougher surface is formed for coating samples subjected to impingement flow. The influence of flow conditions on coating thickness has been monitored. The thickness of the coated samples exposed to the stationary fluid increased after the exposure period. On the other hand, the thickness of the samples decreased after the exposure to the impingement flow. Discussions have been carried out to explain this phenomenon.  


Comparison of Epoxy Coating Degradations Under Impingement Flow and Stationary Immersion

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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