Selection and Construction Strategy of Oil Tank Anticorrosive Coatings

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1. Selection of anticorrosion coating for oil storage tank
 
Electrostatic conductive coating for inner wall According to relevant requirements, electrostatic conductive coating should be used for the inner wall of a crude oil tank. According to different conductive media, common electrostatic conductive coatings for the inner wall of the oil storage tanks can be divided into the following three types:
(1) Non-metallic electrostatic conductive coatings, commonly used non-metallic electrostatic coatings include solvent-free epoxy antistatic oil pipe paint, epoxy phenolic oil tank paint, epoxy oil-resistant antistatic anticorrosive paint;
(2) Metal electrostatic conductive coatings, the color of which is limited by the color of metal powder, have cathodic protection and antirust effect on steel when metal powder with lower potential is used as a medium, and electrochemical corrosion is easy to form if the potential of metal powder is higher than that of steel. The metal powder is easily oxidized, which leads to a decrease in the conductivity of the coating film. Epoxy zinc-rich primer and inorganic zinc-rich primer are commonly used metal electrostatic conductive coatings.
(3) Conductive composite mica powder has the advantages of lasting and effective conductivity, good compactness of paint film and light color, and can be made into electrostatic paint of various colors, but the disadvantage is that it is expensive. Common products include light-colored solvent-free epoxy antistatic oil tank paint, light-colored epoxy phenolic oil tank paint, light-colored epoxy oil-resistant antistatic anticorrosive paint, etc.
 
Anticorrosive coating for the outer wall
In order to meet the requirements of the long service life of oil tanks, the coating should have a long anti-corrosion life. Anti-corrosion coating for the outer wall is divided into three layers: top coat, middle coat and primer, and some oil tanks only have two layers: top coat and primer. Among them, the top coating should be easy to construct and maintain, and polyurethane top coating is usually used. Its advantages are unlimited coating time, good compatibility, excellent oil resistance and solvent resistance, excellent color retention, anti-pulverization, no yellowing and good decoration. Generally, epoxy micaceous iron mid-coat paint with good compatibility with topcoat and good adhesion to zinc-rich primer is used for mid-coat paint. Its main feature is good shielding and impermeability, which can effectively prevent the corrosive medium from entering and corroding the substrate. Commonly used primer materials are inorganic zinc-rich primer and epoxy zinc-rich primer. Because the paint film contains a large amount of zinc powder, it has the advantages of excellent oil resistance, fast drying, rust resistance and cathodic protection. At present, there are many brands in the domestic anti-corrosion coatings industry, and the quality is uneven. In order to effectively guarantee the quality of anti-corrosion coatings for oil storage tanks, the quality of anti-corrosion coatings on the market should be evaluated regularly, and better ones should be selected for the construction of anti-corrosion coatings for oil storage tanks.
 
Construction Strategy of Oil Tank Anticorrosive Coatings
 
Surface treatment
Before the construction of anti-corrosion coating for the oil storage tank, the surface of the oil storage tank should be sandblasted, de-rusted and degreased, so as to ensure that the surface of the oil storage tank is flat, clean and smooth, without burrs, rust spots, electric arc smoke and dust, etc. The primer shall be applied within 6h of surface treatment.
 
Coating environmental conditions
The painting should be carried out in sunny weather, the construction environment temperature should be 5-35, and it is not suitable for construction in rainy, snowy and foggy weather. The painting site should be sheltered and the environment should be clean, so as to avoid rain, snow and dust falling on the wet paint surface, and the indoor air humidity should not be greater than 80%. During construction, the oil tank should be dry and clean.
 
Painting operation process requirements
There are the following three commonly used painting construction methods, each of which has its own advantages and disadvantages. The construction method should be reasonably selected according to the coating performance, construction conditions and construction area.
 
Brush coating method
Workers use paintbrushes for painting construction. During construction, corners, rivet heads and welding seams should be pre-painted and then painted in a large area. In order to ensure that there are no omissions in the painting, vertical painting and horizontal painting should be staggered.
 
Roll coating method
Workers use the roller to dip in the paint for painting, which is faster than the brush painting method. However, when dipping in paint, it should be noted that the whole roller should be dipped in paint evenly, so as to avoid the occurrence of a thick middle, thin sides or a situation that makes the paint beneficial to both sides of the roller. When painting, the roller should move up and down, left and right slowly and uniformly. During construction, the corners, rivet heads and welds shall be pre-coated.

Air spraying method
The air spraying method is generally suitable for large-area construction, and this method has the highest working efficiency. However, during spraying, it should be noted that the distance and angle between the spray gun and the coated surface should always remain the same. During construction, the corners, rivet heads and welding seams should be pre-coated. During the construction process, the constructors should always check the wet film thickness of the coating according to the coating instructions, and convert the dry film thickness, so as to prevent the dry film thickness of the coating from reaching the standard or exceeding the standard. At the same time, it should be noted that the next process can be carried out only after each layer of coating is completely cured and the dry film thickness meets the specification requirements. During the inspection, it should be noted that the selection of measuring points should be uniform and representative, and the parts with dry film thickness meeting the specification requirements should be coated in time.
 
Conclusion
This paper briefly introduces the selection of electrostatic conductive coating for the inner wall and anticorrosive coating for the outer wall of the oil storage tank and analyzes the key points of the construction strategy of oil storage tank anticorrosive coating from three aspects: surface treatment, coating environmental conditions and coating operation process requirements, so as to ensure that the construction of oil storage tank anticorrosive coating can meet the quality requirements.