Discuss the corrosion of light oil tanks

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Let’s discuss the corrosion of lightweight oil tanks. The oil stored in metal tanks often contains certain chemical substances that are corrosive to metals, thereby affecting the service life of these tanks. Metal oil tanks, when left without anti-corrosion protection, are prone to oil leaks, which pollute the environment and affect the safe operation of the storage tanks. 1. Corrosion characteristics of light oil tanks: Light oil tanks refer to tanks used for storing light petroleum products such as gasoline, diesel, and kerosene. Light petroleum products with high volatility, like gasoline, are more corrosive than heavy petroleum products with lower volatility; corrosion is particularly severe in the gas phase area. Due to the high solubility of oxygen in light oil, some of the dissolved oxygen can enter the water at the bottom of the tank; as a result, mild galvanic micro-corrosion and oxygen concentration cell corrosion still occur at the tank bottom. Moreover, the specific corrosion conditions of such oil storage tanks also vary depending on the medium. 2. Corrosion environment of light oil tanks: The internal corrosion of oil tanks is related to factors such as the type and properties of the stored medium, temperature, and the design of the oil tank. There are two corrosion environments inside the oil tank: one is the liquid phase and the other is the gas phase. For oil tanks with a temperature of less than 100°C and a water phase, the liquid phase is divided into two layers; in addition to the oil layer, there is usually a water layer at the bottom of the tank. For fixed-roof oil tanks, the corrosion characteristics in various internal areas are as follows: (1) The tank roof and the upper part of the tank walls: These areas do not come into direct contact with the oil, and corrosion in this area falls under the category of electrochemical corrosion. Corrosion occurs due to a condensation water film, along with the action of harmful gases such as SO2, CO2, H2S, and O2, which lead to the formation of corrosive galvanic cells. Due to the thin water film, oxygen can diffuse easily, so oxygen-consuming corrosion plays a dominant role. Corrosion at the gas-liquid interface on the tank wall is corrosion under oxygen concentration cell conditions, and it is one of the most severe areas of corrosion on the tank wall. ⑵Middle part of the tank wall: The middle part of the tank wall is in direct contact with the oil, and its corrosion is primarily caused by the chemical properties of the oil; thus, the degree of corrosion in this area is the lowest. In oil tanks where the liquid level changes frequently, corrosion at the gas-liquid interface is relatively severe. ⑶Lower part of the tank wall and upper surface of the tank bottom plate: These areas suffer the most severe corrosion inside the oil tank, primarily due to electrochemical corrosion. Typically, oily wastewater contains Cl- and sulfate-reducing bacteria, as well as harmful gases such as SO2, CO2, and H2S, making it highly corrosive. Differential corrosion occurs at the interface where oil and water meet on the lower part of the tank wall and the upper surface of the tank bottom plate. Therefore, by clearly understanding the corrosion characteristics of light oil tanks as well as the corrosion environments in which they operate, and by grasping the mechanisms of corrosion, it is possible to adopt effective protection methods to improve the service life of these storage tanks.