Corrosion and Anti-corrosion Measures of Oil Storage Tanks

With the development of the economy, almost every household has a car, so the big environment has created the development of the oil industry. People need to reserve oil and can’t put it into use immediately after exploitation, so oil storage tanks are usually used to store oil in the oil industry. The corrosion degree of oil storage tanks can directly affect the development of the petroleum industry, but the corrosion phenomenon of oil storage tanks in use is extremely common, which requires us to carry out anti-corrosion work when using oil storage tanks to avoid the perforation of oil storage tank walls and ensure the safety of people’s property and life.

Usage of oil storage tanks and causes of easy corrosion

Oil storage tanks play an important role in China’s petroleum industry. Many oil fields, oil refining companies and oil production bases will put oil storage tanks in large quantities. According to the different ways of using oil storage tanks, we can divide them into two types: floating roof tanks and dome tanks. According to their size, we can basically divide them into four types: small, medium, large and extra-large. Generally, we use dome tanks in oil fields, which we can use them to store crude oil, and the size will depend on the amount of oil.

In addition, some refineries will use oil storage tanks to store sewage containing chemicals. As the liquid stored in the oil storage tank has certain corrosiveness, it can be classified into consumables, and the general service life is within 5 years. If we can take anti-corrosion measures properly, we can appropriately extend the service life. The main reason why oil tanks are easy to corrode is that the stored liquid contains corrosive impurities such as hydrogen and sulfur compounds, and it is also easily disturbed by the external environment. Therefore, China has been studying the measures to prevent corrosion of oil tanks.

Corrosion-prone parts of oil storage tanks

1. Outer wall of oil storage tanks

According to the present situation, the outer wall of the oil storage tank is extremely easy to corrode. Generally, the external environment mainly cause the corrosion of the outer wall. The longer we expose the oil storage tank to sunlight, the more serious the corrosion degree of the outer wall will be.

In the refinery where the oil tank is stored, the outer wall will be corroded by chemical gas; If the oil storage tank is placed near the sea, the outer wall will be corroded by the atmosphere; Besides, the corrosion degree of the outer wall of the oil storage tank will be more serious in the humid cities in the south. The humid environment contains a large number of water molecules, which will form a water film on the metal surface of the oil storage tank, resulting in the electrolysis of water, and the chemical reaction will cause the outer wall to be corroded.

2. Inner wall of oil storage tanks

Except that the top of the inner wall of the oil storage tank will not be in direct contact with the oil, other parts will get along with the oil for a long time. The most seriously corroded is the bottom of the inner wall, followed by the top area of the tank. Although we weill store different liquids in the oil storage tank, they basically have some corrosion effects.

For example, water and other elements such as acid, alkali and salt will lead to electrolytic water on the inner wall, which will corrode the inner wall out of the pit, directly penetrating the pipe wall for a long time, resulting in leakage. In addition, there is plenty of oxygen at the top of the tank, but the uneven concentration distribution often occurs, which leads to the corrosion of the parts with low oxygen concentration. The mixed gas produced in the air gap will also have different chemical reactions, resulting in the corrosion of the tank top area.

3. External bottom of oil storage tanks

Generally, the factory will bury the bottom of a large oil storage tank underground, in which case the outer bottom of the oil storage tank is particularly vulnerable to corrosion. The oxygen concentration in the soil is not enough, so it will cause battery corrosion; When the water in the soil combines with the air to form other chemical reactions, it will also corrode the outer tank bottom; When the oil storage tank is in the open air and rain, snow, hail, etc., the electrochemical response will also appear at the tank bottom, which will lead to corrosion of the external tank bottom.

Basic measures for anticorrosion of oil storage tanks

1. Applying anticorrosive materials evenly on the outer wall

When we carry out anti-corrosion work on the outer wall of oil storage tanks, we can coat some anti-corrosion materials on it. These materials should have excellent anti-oil and anti-fouling properties, which is convenient for subsequent maintenance and secondary painting. In addition, for oil storage tanks bathed in sunshine for a long time, when coating anti-corrosion materials on the outer wall, it should also have the effect of preventing sun and adapting to the temperature.

Try to choose some materials that are not easy to be steamed in the sun and have less hair loss, such as dark anti-corrosion coatings. In this way, it is necessary to consider whether the anti-corrosion coating has fire resistance and expansion function when selecting it. This kind of coating can not only prevent corrosion and reduce heat radiation but also reduce the temperature to prevent the burning phenomenon caused by excessive temperature. At the same time, this kind of coating is a green and pollution-free anti-corrosion coating.

2. Painting internally

For the inner wall directly in contact with oil, different anti-corrosion measures should be adopted according to different parts.

(1) For the bottom of the inner wall, a coating with impermeability can be used to reduce the record of medium corrosion, and a high-potential coating can also be used. The conductive material is used as the bottom of the inner wall of the oil storage tank, which can effectively avoid iron as an anode;

(2) For the roof area of the inner wall of the tank, a resistance film with a resistivity of about 106° can be used to prevent static electricity from agglomerating together. When the anticorrosive coating is used, it should have a good effect on blocking the corrosion of chemical gases. At the same time, it should be ensured that the coating has no pollution to oil products;

(3) For other inner walls in contact with oil products, besides using the above-mentioned resistance film, it is necessary to ensure that the used anti-corrosion coating does not damage the inner wall steel and pollute the oil products, so as to prevent the steel from being corroded by the coating from the source.

3. Improve the environment at the bottom of the outer wall

When anti-corrosion work is carried out on the bottom of the outer wall of the oil storage tank, it can be carried out from the following three aspects:

(1) Improve the soil environment at the bottom of the outer wall. When burying the bottom of the outer wall of the oil storage tank, try to bury it in the sand. This kind of soil has a general water storage effect, which is conducive to reducing the corrosion degree of the bottom of the outer wall. Cement is injected into the surface of the land to form a cement field, which is conducive to reducing the infiltration of rainwater and other water into the soil, as shown in Figure 1;

(2) Increase the coverage of the protective layer. When the protective layer is added, some other substances containing polyethylene, such as glass fiber and plastic bags, can be added to reinforce the protective layer.

(3) Adopt cathodic protection. Cathode protection can improve the phenomenon of the insufficient protective layer, and can also ensure that underground structures are not damaged, which has a preventive effect.

Fig. 1 Oil storage tanks placed in cement ground

As the corrosion of oil storage tanks has a great influence on oil enterprises, once the oil leakage happens without anti-corrosion measures, the life safety of people nearby will be threatened, so our country attaches great importance to the anti-corrosion measures of oil storage tanks. With the development of science and technology, the anti-corrosion technology of oil storage tanks will be improved in the future, and technicians will constantly innovate and practice this problem to protect people’s lives and property in an all-around way and help the stable development of the oil industry.