Rapid Assessment Technique To Evaluate Corrosion Resistance Of The Steel Members Coating System In The Hot And Humid Maritime Environment

In the study of coating protective performance of sea wind power steel structure, the most commonly evaluation methods are conventional standard tests, including salt spray test, immersion test, damp heat test, natural exposure, artificial ultraviolet aging resistance experiment and so on. These methods are not only inconvenient to field test, but also time-consuming, low efficiency and high cost, for example, salt spray test normally need 5000 h, and natural exposure test cycle need at least 12 months. Electrochemical impedance spectroscopy(EIS) is a kind of burgeoning and promising rapid evaluation method. Early data process method of EIS is equivalent circuit simulation program, now this method is being replaced by characteristic frequency method and phase angle method because of its complex, low accuracy and the high requirement of experience, but these rapid evaluation methods are just based on a part of EIS points, and inconvenient to field test too. Therefore, in this paper, coating performance will be evaluated rapidly by analysis the area change rate under the impedance spectroscopy Bode diagram line. In our country, few researchers refer to this method.In this paper, altogether six kinds of classic coating systems selected from sea wind power steel structure atmospheric zone and splash zone had been evaluated by conventional test and area change rate under Bode diagram line, then compare the rapid evaluation results with the conventional test results to verify the rapid evaluation method is feasible. At the same time, combined with EIS characteristics in the different corrosion stages, the feasibility of rapid assessment method has been verified by analysis the change of microstructure of these coatings. Main conclusions of this paper as follows:(1) The corrosion resistance and aging resistance of atmospheric zone coating system had been evaluated by 5000 h salt spray test and 2000 h artificial ultraviolet aging resistance experiment. And the corrosion resistance and water resistance of splash zone had been evaluated by 5000 h salt spray and 5000 h immersion test. At the same time, all the coating system is evaluated by natural exposure experimental. Results show that the comprehensive performance of three samples selected from atmospheric zone rank in sample 1(EP150 epoxy zinc-rich/ZSS 132 epoxy mica iron oxide/ UL800 H fluorocarbon)>sample 2(102 HS epoxy zinc-rich/ epoxy mica iron oxide/fluorocarbon)>sample 3(epoxy zinc-rich/ epoxy mica iron oxide/fluorocarbon). For the splash zone coating systems, sample 5(epoxy/ abrasion resistance epoxy) > sample 4(high build epoxy / epoxy glass flake) > sample 6(epoxy/ abrasion resistant epoxy glass flake).(2) EIS of six coating systems after 24 h, 360 h and 720 h artificial seawater immersion corrosion had been test by Princeton electrochemical workstation, calculate the area change rate under Bode diagram line. Integrated data processing results, the area change rate of atmospheric zone and splash zone coating system respectively rank in sample3>sample2>sample 1, sample 6>sample 4>sample 5. From the relationship between area change rate and coating performance known that the rapid evaluation results accordance with the conventional test results, shows that using the area change rate rapid evaluate coating performance is completely feasible. Moreover, the experimental period of rapid evaluation is 720 h, only 1/7 of the salt spray, and far less than natural exposure.(3) Electrochemical test equipment has achieved miniaturization, test duration generally need half an hour to 2h. Combined with data processing software, can evaluate coating performance at the project field. Conventional experiment need professional equipment, natural exposure need standard experimental base, test chamber and other equipment need to maintain long-term stability during the operation of salt spray experiment and ultraviolet aging experiment. These high requirements lead it unsuitable to evaluate servicing coating performance at the project field.(4) The corresponding microstructure characteristics of EIS of different corrosion stages had been studied by SEM, further confirmed the feasibility of electrochemical fast evaluation method. Conclusions as follows: the microstructure of coating will occur a series of change during it failure process, cause the coating performance decline at the same time. These changes will be reflected in the EIS, namely curves and area under line drops. Therefore, this rule fit with the rapid evaluation theory, the rapid evaluation based on area change rate under Bode diagram line is completely feasible.