Water percolation into coating-metal interface is usually the main cause for the deterioration of corrosion protective property of organic coatings, which leads to coating delamination and under film corrosion. Recently, flowing fluid has received attention due to its capability to accelerate the degradation of materials. A plethora of works have focused on the corrosion of metallic materials accelerated by the flow of working fluids, while few studies have investigated the flow accelerated degrading behavior of organic coatings. For organic coatings, flowing fluid above the coating surface affects corrosion by enhancing the water percolation and by abrading the surface due to wall shear stress. Hence, it is of great importance to understand the influence of flowing fluids on the degradation of corrosion protective organic coatings.
In this study, a commercially available epoxy based clear coating and pigmented marine coating were exposed to the laminar flow as well as stationary immersion. The laminar flow was pressure driven and confined in a newly designed flow channel. A 3.5 wt% sodium chloride solution was employed as the working fluid with a variety of flow rates. The corrosion protective properties of organic coatings were monitored inline by Electrochemical Impedance Spectroscopy (EIS) measurement. Equivalent circuit models were employed to interpret the EIS spectra. The time evolution of coating resistance and capacitance obtained from the model was studied to demonstrate the coating degradation. Thickness, gloss, and other topography characterizations were conducted to facilitate the assessment of the corrosion. The immersing solutions were measured by pH and conductivity meters as well as Fourier Transform Infrared Spectrometer (FTIR) to trace coating degradation products as they leached out from the coating. Initial attempts to acquire acceleration factors and predict service lifetime of organic coatings were also conducted.