Influence of impingement flows with sand particles on the barrier properties of organic coatings

The installations of offshore wind farms, especially the type with monopile structures, increase the number of suspended particles in the surrounding area. The offshore wind structures are usually coated with several layers of coatings, including a thin layer of organic coating as a topcoat. In this study, we aim to investigate the influence of the stresses on the organic coatings due to the kinetic energy of the suspended sand particles. To accomplish the goal, impingement flow jets with particles were applied on coated steel samples for a week in a lab-scale impingement chamber. The working fluid for the experiments was 3.5 wt% NaCl solution with 1 wt% suspended sand particles. Electrochemical impedance spectroscopy (EIS) was conducted to monitor the degradation of organic coatings while exposed to the impingement flow. Computational fluid dynamics (CFD) modeling was utilized to calculate the magnitude of the applied fluid stresses on the coatings. Thermodynamics of electrochemical reactions and the activation theories were utilized to compare with the electrochemical parameters. It was concluded that for the lowest flow rate (Q₁ = 6.31 cm³/s), the added sand particles started to show destructive influence after the first three days of exposure. As the flow rate increased, the destructive influence of sand particles on coating samples appeared earlier at the beginning of the exposure, and the elements of equivalent circuit model showed larger difference between coatings exposed to pure NaCl solution and those exposed to solution with sand particles. For the highest flow rate (Q₃ = 18.93 cm³/s), the destructive influence of sand particles was significant, indicating that for the particulate flows with the velocity of 1 m/s, which is the regular velocity of the underwater zone in shallow sea regions (with a depth of 30 m), the momentum impact of the sand particles plays a vital role in the degradation of the organic coatings.