Recent Progress and Comprehension of Corrosion of Steels in the Hot-Dip Galvanizing Industry

Industrial Hot-dip galvanizing is the process of coating metals (steels) by immersing it in a bath of molten zinc. There are three fundamental steps in the hot-dip galvanizing process: “surface preparation, galvanizing, and inspection”. When the fabricated steel arrives at the galvanizing facility, it is hung by wire or placed in a racking system which can be lifted and moved through the process by overhead cranes. The steel then goes through a series of three cleaning steps; “degreasing, pickling, and fluxing”. Degreasing removes dirt, oil, and organic residues, while the acidic pickling bath will remove mill scale and iron oxide. The final surface preparation step, fluxing, will remove any remaining oxides and coat the steel with a protective layer to prevent any further oxide formation prior to galvanizing. Proper surface preparation is critical, as zinc will not react with unclean steel. The purpose of this book chapter is to review the effect of silicon and phosphorus content in steel suitable for industrial Hot-dip galvanizing on its corrosion and to study a newly 5-p-tolyl-1H-tetrazole (PT) used as corrosion inhibitor of steels in industrial hydrochloric acid pickling. All the methods used are in reasonable agreement. Results show that the corrosion inhibition 82properties such as inhibition efficiency, polarization resistance and thickness of the electrical double layer for PT/Steel Class A system are better than PT/ Steel Class C system depending on the steels silicon and phosphorus content. On the other hand, it is observed that the electrolyte solution increased with the 5-p-tolyl-1H-tetrazole (PT) inhibitor addition. This can be explained by the protonated of the 5-p-tolyl-1H-tetrazole (PT) inhibitor molecules decreasing therefore the concentration of the H+ ions in the solution. It is also noted that the 5-p-tolyl-1H-tetrazole (PT) inhibition efficiency of steel class A is more that for steel class C.