STUDY ON CORROSION BEHAVIOR OF HOT DIP COATINGS IN WET-DRY CYCLIC CONDITIONS

The corrosion of fasteners in ballast tank is much serious, due to the wet-dry corrosive conditions. Now most fasteners are protected by zinc-aluminium coating. In order to evaluate the anticorrosion performance of hot dip Galvanized (GI), Galfan (GF) and Galvalume (GL) coated fasteners in wet-dry cyclic conditions, the corrosion behavior of these coatings in 1h wet and 7h drying condition were investigated by electrochemical impedance spectroscopy technology. The corrosion rate of GI coating in drying condition is much faster than that in wet condition before 23rd cycle, after that time the corrosion rate in sea water is faster than that in drying condition, however the corrosion rate of GF coatings in drying condition is much slower than that in wet condition, and for GL coating, the polarization resistance is both than 10(4)Omega.cm(2), whether it is immersed in seawater or in drying condition, which suggests it has better anticorrosion performance. The corrosion rate of the GI, GF and GL coating is 30 mu m per year, 1.5 mu m per year and 1.3 mu m per year respectively and corrosion resistance of GL and GF is therefore twenty two and twenty times as that of GI.