Corrosion Resistance Evaluation of Zinc coatings on Mild Steel Substrate for Soil Applications
Keywords:Cold Galvanizing, Epoxy Zinc Coating, Electrochemical Impedance Spectroscopy (EIS), Open circuit potential (OCP)
The underground and over-ground pipelines and structures are extensively used for transporting natural gas and oil are made of expensive steel alloys. They are used in many aggressive media: sea water, soil, marine and industrial environments. Because of the presence of salt content and other atmospheric factors, the pipeline goes under severe corrosion problems. This causes pits and holes in pipe surface making it useless and causing a huge loss of money and time. This study aimed to corrosion resistance evaluation of different zinc coatings (cold galvanized and zinc electroplating) on mild steel substrate for soil applications. Two types of coatings were deposited on mild steel substrate cold galvanized zinc coatings and industrial grade electroplated zinc coating. Cold galvanized zinc coatings were applied on substrate using two methods; brushing and dipping. Corrosion behavior of the zinc coated and uncoated mild steel samples was assessed in prepared soil by open circuit potential (OCP) and Electrochemical impedance spectroscopy (EIS) at 0 and 24hours. Â The EIS study revealed that all types of zinc coatings have barrier properties in prepared soil. Cyclic polarization revealed that cold galvanized zinc coating produced by brushing was highly susceptibility to pitting. Cold galvanized dipped coating behaved well in the electrochemical testing and proved to be the best coating in prepared soil. The high coating thickness, uniform coating over substrate and low surface roughness were the main factor contributed towards its better corrosion resistance than the other coatings in prepared soil.
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