Study On Corrosion Failurerelationship Of Organic Coating Protective System Under Different Environments

The organic coating protection system has many advantages such as long-term protection,economical and practical,energy saving and environmental protection,etc.The organic coating protection system is the most widely used metal anti-corrosion method.China has a vast territory,and its natural conditions are complex.There are huge differences in the atmospheric environment between different regions.Therefore,it is meaningful to make a comprehensive evaluation of the corrosivity,to study the different failure modes and failure mechanisms of the coating protection system,and to predict the service life of the coating protection systems under different atmospheric environments.In this paper,radar chart analysis method is used to select comprehensive evaluation of different atmospheric environments in six aspects:ambient temperature,ambient humidity,ultraviolet radiation,chloride ion deposition,oxidizing,and acidity.According to the corrosivity of the environment,develop a corresponding accelerated environmental test spectrum,and compared it with natural atmosphere.Accelerated corrosion tests which combine with ultraviolet radiation test,cyclic immersion test,and blow sand test were performed on different organic coating protection systems.Analyze the difference in the failure modes of the coating protection system under different environments.Analyze the failure mechanism of the coating system under different environments by scanning electron microscopy,atomic force microscopy,infrared spectroscopy,and electrochemical impedance spectroscopy.Finally,by comparing the experimental results of accelerated corrosion test and atmospheric exposure test,the equivalence between the them was obtained.The results show that there are significant differences in the corrosivity of different atmospheric environments.The marine atmospheric environment has the characteristics of high temperature,high humidity,and high salinity.The industrial atmospheric environment has high content of salt and contains strong acidic SO2 gas.The urban atmospheric environment contains high concentrations of nitrogen oxides,which have strong oxidation.The plateau atmospheric environment is pretty dry and the ultraviolet radiation is extremely strong;the desert environment is hot and dry,ultraviolet radiation is strong,and there are extreme weather conditions such as dust storms that cause severe physical aging of the coating system.In the coating failure mode:the marine atmospheric environment mainly manifested as the gloss lose,thickness reduced,adhesion reduced,blistering,and powdering;the urban atmospheric environment and industrial atmospheric environment are mainly manifested as blistering and pulverization.There will be a small amount of blistering in the coating system of plateau atmospheric environment.In general,the corrosion of the coating system is not strong.The desert environment is mainly manifested as by gloss loss,thickness reduced,adhesion reduced,and chalking.In terms of the corrosion mechanism:under various circumstances,the C=O bond,N-H bond,and C-O bond of the coating surface were weakened.The failure of the marine atmospheric environment is mainly caused by the infiltration of corrosive media.A large number of continuous blisters appear on the coating surface,and a large number of micropores are generated due to the blisters."The surface roughness of the coating increases."There was also a large amount of blistering in the urban atmospheric environment and the industrial atmospheric environment,but the blistering was not obvious,and no micropores appeared on the surface of the coating.For the strong oxidation in the urban atmospheric environment,the unsaturated bonds of the coating,such as C=C bonds and C=O bonds,were weakened significantly.In the plateau atmospheric environment,only a few blisters appeared on the surface of the coating,the surface roughness did not increase,and the chemical bonds did not be weakened significantly.In the desert atmospheric environment,the surface of the coating is severely damaged by the dust and the surface roughness is extremely high.Compared the accelerated corrosion test with the natural exposure test of coating systems.Considering the changes of coating gloss,thickness,electrochemical impedance,the relationship between the accelerated corrosion test and the natural exposure test is about 0.65-0.7.