Ship's water ballast tanks are exposed to the extremely corrosive environments due to immersion or non-immersion by cyclic loading/unloading of ballast water. For cargo oil tankers, the temperature of the ballast tanks walls adjacent to the cargo oil tanks can reach up to 60° and drop to 0° in the cold sea causing higher hostility of corrosive environment. In ageing ships, coating failures, such as cracking, peeling off, are often observed in the areas of erection jointed weld seams and other stress concentrated areas.
To improve coating performance of these vulnerable areas, the current surface preparation methods and coating materials for the erection jointed seams of water ballast tanks are evaluated. Three types of surface preparation tool were tested and evaluated in terms of surface profile and subsequent coating performances, such as long term corrosion resistance, crack resistance, rust creepage, cathodic disbondment test, etc. From these results, optimum surface preparation methods and proper coating materials for erection jointed seams of water ballast tanks are proposed.
To achieve good coating adhesion, steel substrate must have proper roughness in order to provide an increased effective surface area for mechanical bonding. This roughness, also known as anchor pattern or surface profile, forms micro pattern of peaks and valleys at the surface, which can be obtained via power-tooling methods when an abrasive blast cleaning is not practical due to limited accessibility [1]. The surface preparation of a ship's erection weld joints is a typical example, where the complexity and heavy weight of the process equipment for abrasive blasting cause poor accessibility to complicated and huge marine structures. Therefore, as an alternative, power tooling has been increasingly used for the surface treatment of some areas of marine vessels and offshore structures such as welded joints after erection. It has been known, however, that the conventional power tooling method provides less favorable final coating quality than the abrasive blasting method, probably due to its inferior surface profile. However, C. S. Park et al.[2] showed that proper selection of coating material itself, such as surface tolerant type, will also provide better long-term coating performance upon employing power tooling surface treatment. These results suggest that a certain type of power tooling method could be a reasonable alternative to abrasive blasting in the surface treatment of marine structures in their erection stage such as erection welded joints.
Water ballast tanks(WBT) in ships are exposed to extremely corrosive environments due to cyclic loading/unloading of ballast water. Especially, for the cargo oil tankers, the temperature of the ballast tanks adjacent to the cargo oil tanks can reach up to 60° and drop to 0° in the cold sea. Therefore, the inner water ballast tank surface area is very hostile to a coating's performance.
