Research On Immersed Thermal Aging Of Coatings In Nuclear Power Plant

In the current anti-corrosion field, the most widely used technology is organic coatings. It’s also the most cost-effective and most comprehensive protection technology. The most largely used organic coatings in the nuclear power plant are epoxy resins, polyurethanes, rubber resins and phenolic resins. The researches on special coatings for nuclear power plants since the late twentieth century have helped to dramatically reduce the losses caused by corrosions. Epoxy resin coatings are particularly outstanding during their applications in nuclear power plants.In this paper, the research object is the solidified coatings of Bitumastic 300 M and Bitumastic 50, hereinafter called BT 300 M and BT 50, all produced by the Carboline Company. The samples are in the form of unsupported films, which are black and opaque. BT 300 M is an epoxy resin, but BT 50 is not. The two coatings are mainly used in the outer surfaces of steel pipes in the third loop of nuclear power plant: service temperature 25 ~ 50 °C, relative humidity 50%, thickness 500 ~ 800 μm, service life 25 to 30 years.The coatings are used to protect the pipeline and prevent it from corrosions. They should be able to suppress the diffusion of water and oxygen into the interface of coatings and pipes. In this interface, the combination of water and oxygen can cause electrochemical corrosions of steel pipes.Due to time constraints and the experimental conditions, we mainly consider the acts of water and oxygen on coatings and test the properties of coatings themselves. The samples are completely immersed in water at different temperatures. We raise the temperature and the humidity to accelerate the aging process.Through the vacuum drying and water absorption experiments, we study the water absorption abilities of BT 300 M and BT 50 at 70°C and calculate the water diffusion coefficient of BT 300 M. We also study and master the acts of post-crosslinkings and evaporations of solvents on the water diffusion process in BT 300 M.During the immersed aging process up to 2400 hours at 70°C and 90°C, we analyze the infrared spectra of samples and find that the spectrum of BT 300 M doesn’t change much and only the concentrations of hydroxyl(-OH) slightly increase. We also find that BT 300 M is not very sensitive to the difference between two experimental temperatures. BT 50(Tg:-7.39°C) is in the rubbery state at ambient temperature, but it becomes very fragile during the immersed aging experiment.