Corrosion Resistance Evaluation of Zinc Coatings on Mild Steel Substrate for Marine Applications

Muhammad Hamza Ayyub, Asma Salman, Jawad ahmad, Ameeq Farooq, Arshid Mahmood Ali

Abstract


Steels are the most important structural materials and their corrosion problems must be considered during industrial and marine applications. Corrosion protection of over-ground and underground structures by protective coatings is one of the most proven methods. Zinc rich coatings are being used by many industries for the corrosion protection of steel substrates. This study looked at corrosion resistance evaluation of different zinc coatings (cold galvanized and zinc electroplating) on mild steel substrates for marine applications. Cold galvanized zinc coating was applied by two methods; brushing and dipping. Electrochemical techniques were utilized to assess the corrosion resistance of different zinc rich coatings in medium of 3.5%w/v NaCl solution. The tests were done at 0 hour exposure and 24 hours exposure in 3.5% NaCl solution as a corrosive medium. Salt spray test was also employed to get the corrosion resistance comparison of the coatings carried out for 500 hours. Open circuit potential revealed that all the zinc rich coatings were sacrificial in nature. Electrochemical impedance spectroscopy also revealed that their corrosion resistance increased after 24 hours of exposure in 3.5% NaCl solution due to the formation of corrosion product. Pitting susceptibility of coatings was also evaluated by cyclic polarization. The visual inspection of salt spray samples clarify the results of electrochemical testing by showing most of the white rust as corrosion product. The results of both electrochemical and salt spray testing indicated, cold galvanized zinc coating applied by dipping as the best coating for marine applications.

 


Keywords


Cold Galvanizing, Epoxy Zinc Coating, Electrochemical Impedance Spectroscopy, Marine Applications, Open circuit potential



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