Research On Corrosion Of Ballast Tank And Coating Protection In Seawater Electrolysis

The marine organism invasion caused by ship ballast water has been considered as one of the four threatens to harm ocean by Global Environment Facility (GEF). Regarding the organism invasion, the international maritime organization (IMO) went through The Convention on the control and management of ship's ballast water and sediments (hereinafter referred to as the convention) in February 2004. The Convention shall enter into force twelve months after the date on which not less than thirty States, the combined merchant fleets of which constitute not less than thirty-five per cent of the gross tonnage of the world's merchant shipping. There are twenty-five Contracting States to the Convention, representing approximately 24.28% of the gross tonnage of the world's merchant shipping, the Convention will enter into force soon.Among all kinds of ship ballast water treatment technology, ballast water online electrolysis technology has become one of the two main ship ballast water treatment technologies (another one is based on UV treatment technology). Therefore, it appears increasingly important and urgent for the study of metal corrosion and coating failure caused by ballast water electrolysis treatment technology.For ballast tank corrosion and coating protection during the process of ship ballast water electrolytic treatment, the followings were studied:1) Water ballast tank corrosion under different environmental factorsThe study mainly contains:laboratory metal immersion experiment under different water temperature and total residual chlorine. Electrochemical impedance spectroscopy (EIS) method is used to study the metal corrosion under different residual chlorine concentration of electrolyte seawater. Combined with weight-loss experiment, this paper studied the environmental factors effect on carbon steel corrosion. The results show that with the increase of residual chlorine concentration and temperature, carbon corrosion rates is increased.2) Experimental study of coating EIS behavior under different residual chlorine concentration of electrolyte. Equivalent circuit method was used to analysis the dynamic parameters. In addition, using high frequency phase, low modulus characteristic parameters, combining with open potential changes and sample of organic coatings corrosive morphology observation, the corrosive medium diffusion law in coating and the influence mechanism of the residual chlorine to coating failures were discussed. The results show:The water absorbing of coating mainly depends on water diffusion, irrespective of residual chlorine at the beginning time of immersion. However, when the solution come to the metal surface it has something to do with osmotic pressure:the higher the residual chlorine concentration, the more serious corrosion, the higher forming the corrosion product salt solution concentration, the higher osmotic pressure, the more serious destruction of coating.