An Experimental Study On The Corrosion Mechanism And Protective Coatings Of Offshore Tank Wall Under The Atmospheric Environment

Oil tanks are critical facilities, which is broadly applied in oil exploration, transportation, storage, processing of vital infrastructure, and have serious impact on the stability of the operation of the entire oil and petrochemical system. When oil tanks are placed in offshore environment, due to the high air humidity and the salt concentration, its wall can be easily corroded. Thus research on factors affecting the corrosion of steel tanks is an important guiding significance. Among a wide variety of protection methods, the protective coating is one of the most widely used and efficient. And as there are so many types of market available coatings, of which performance vary greatly, it’s significant to design a reasonable protective coating systems for reducing losses caused by corrosion.This paper is part of the project " A study on anti-corrosion technology for oil tanks and steel in offshore atmosphere ". Firstly, the effects of temperature, humidity and chloride ion concentration on corrosion behavior of the active material Q235 was studied through the salt spray test. Results showed that: the corrosion rate of Q235 steel increased with the temperature rises in a range of 25 ~ 40 ℃; when sodium content in the range of 0.875% to 7%, the corrosion rate of Q235 firstly increased and then decreased, showing a parabolic trend, appear extreme in the mass fraction of 1.75%. Always settlement compared to salt spray environment, alternating wet and dry etching rate increases in Q235. After that, according to the target level of atmospheric corrosion for C5-M-class, four different coating systems was designed for the zinc-rich epoxy primer, epoxy intermediate coat iron, acrylic polyurethane topcoat(APU1) from Tianjin, fluorocarbon from Tianjin(FC1), acrylic polyurethane topcoat from Qingdao(APU2), topcoat is fluorocarbon from Qingdao(FC2). The total dry film thickness was designed as 320 μm. Their performance were evaluated by salt spray test, UV aging tests and immersion tests. The results showed that : APU1 showed the best anti-aging performance, which was followed by FC1, and APU2 and FC2 acted worst; FC1 has a relatively good salt spray resistance, APU1 followed, APU2 and FC2 worst; APU1 has a best resistance to neutral immersion, which is serially followed by FC1, FC2 and APU.