Study On Corrosion Failure Behavior Of Ship Ballast Tank Coating Under Different Conditions

Ballast tank is usually one of the most serious corrosion cabins in ship and offshore platforms. It will be affected by structure stress, ballast water temperature change and the cathodic protection and these factors can cause damage to its protective performance of the coating. This thesis was mainly studied by electrochemical impedance spectroscopy (EIS) to research the influence of different stress, cathodic protection potential and solution temperature on the performance of ballast tank coating. Through the analysis of measured data and the measurements of coating adhesion, thereby the influence of various factors on coating failure was carefully analyzed.1. The coating samples were divided into two groups, A and B and the failure process of the two groups that immersed in 3.5% NaCl solution under different magnitudes stress was studied by EIS. The results show that both tensile and compressive stress can cause damage to the protective properties of the coating. The effect of compressive stress on the failure process of the coating increases as the stress increases initially but the effect decreases afterwards. The effect of tensile stress increases with the increase of stress amplitude. The contrast effect of compressive stress and tensile stress of the same amplitude on the performance of coatings shows that the coating sample affected by tensile stress is easier to fail.2. The protective performance failure of ballast tank coating under different amplitude of cathodic protection potential was studied by EIS method. The result shows that cathodic protection can significantly reduce the coating protection performance. The effect of stress on the failure of ballast tank coating under the cathodic protection is also studied. It could be found that the tensile stress will accelerate the failure rate of the coating which is protected by cathodic protection. However, the effect of this acceleration will gradually become less obvious with the decrease of the potential.3. EIS test was carried out on the ballast tank coating that immersed in different temperature corrosion solution. It was found that the temperature of the solution had a great influence on the water absorption of the coating at the beginning of the immersion. The coating water absorption rate with high temperature solution was significantly higher than that of the coating sample with lower solution temperature. Integrating the whole test process, it was showed that the higher the temperature, the faster the protective properties of the coating decreased. It indicated that the increase of solution temperature would speed up the process of coating failure.