Abstract
Insulation panels are fitted to the inner hull of LNG carriers by bonding with a load bearing epoxy mastic adhesive onto the inner steel surface of the double hull. The steel surfaces of the hull are usually protected after blast cleaning with a wash primer. The adhesion strength between the steel surface and the primer will depend on various conditions; a number of factors will affect the adhesion such as steel surface preparation, the film thickness and types of primer used.
In this study we evaluated the adhesion strength and their corrosion properties at different film thickness for each of the primers used, and also the method of surface preparation used for the steel substrate. In addition we evaluated the temporary anti-corrosion properties of primers by carrying out comparative tests, which has been used for a similar purpose in the past.
Adhesion strength of both primers to surfaces prepared by power tool grinding shows superior adhesion than that of blast cleaning, this is due to power tool grinding providing a more efficient anchor pattern. In case of where the coating thickness is lower than the physical roughness of steel surface, the corrosion resistance of the specimens prepared by power tool grinding is higher than those prepared by blast cleaning. Also, the microstructure and hardness of steel substrate influences the formation of the anchor pattern. Therefore, the hardness of the steel substrate should be considered when selecting the most appropriate method of surface preparation. In case of DFT less than 75µm wash primer shows better corrosion resistance than epoxy Zn primer. However, at higher DFT epoxy Zn primer shows considerably increase in corrosion resistance.
