The selection and application of anticorrosive coatings for oil tanks

The development of society has led to the continuous expansion of demand for petrochemical products, the development of market economy has accelerated China’s construction of oil fields abroad, and the country’s security guarantees have also increased energy reserves.

The design life of the oil storage tank is generally 20 years.

1.

The corrosion of the outer wall of the oil tank is caused by the external environment in which it is located

The medium stored in the tank includes crude oil, gasoline, diesel, kerosene, naphtha, residual oil, slop oil, etc.

Second, the choice of oil tank anticorrosive paint

Oil tank is a large-scale device, and its construction, maintenance and renovation are relatively difficult.

2.

The construction of modern tank farms requires that the outer wall anticorrosion coatings of oil tanks have good protective functions, and the anticorrosion coatings are also required to have decorative properties that meet the design requirements, such as color and gloss

2.
2 The methods to evaluate the weather resistance of anticorrosive coatings include atmospheric aging test and artificial aging test
.

The anti-corrosion coating on the outer wall of ships in China is evaluated by atmospheric aging test according to 6B/T6745 "General Technical Conditions for Ship Hulls".
The general preparation method of the film is used to make the board, and then the test is carried out according to 6B/T9276 "Coating Natural Weather Exposure Test Method", after 12 months of natural exposure in Guangzhou area, and then evaluated according to 6B/T1766 "The Weather Resistance Rating Method of Paint Film" , It is required that the color change of the paint film does not exceed level 4, and the chalking level is qualified
.
At present, there is no national standard for anti-corrosion coatings for the outer walls of oil tanks.
When choosing anti-corrosion coatings for the outer walls of oil tanks, the index of the anti-corrosion coatings for the hull can be used as the minimum requirement for the weather resistance of the selected coatings; or GB/T9757 " The artificial aging index of the superior products in the solvent-based exterior wall coatings is 1000h resistant to artificial weathering.
The coating does not blisters, peels, cracks, pulverization is not greater than level 1, and discoloration is not greater than level 2.
Select the reference standard for the weather resistance of the coating
.

2.
3 Shielding function
.

The anti-corrosion effect of the anti-corrosion coating is achieved through shielding, corrosion inhibition, and cathodic protection.
The shielding effect is to prevent water, oxygen, ions, etc.
from passing through the coating to the metal surface, preventing their infiltration and causing corrosion; Corrosion and cathodic protection are the functions of corrosion inhibitor pigments and active metal fillers in the coating
.
Generally, the base coat (coating that touches the metal surface) plays a role of corrosion inhibition and cathodic protection, and the middle coat and top coat play a shielding role.
When choosing an anticorrosive coating for the outer wall of an oil tank, different shielding functions should be selected according to different environments The shielding function of the anti-corrosion coating is mainly determined by the cross-linked structure of the film-forming base material.
Generally, the resin with a neat molecular structure and few hydrophilic groups on the molecular chain will be shielded after the film is formed.
Good functions, such as fluorocarbon coatings, chlorinated rubber coatings and vinyl coatings
.

Anti-corrosion paint and coating structure suitable for the outer wall of oil tanks in different environments.
Dry and less rainy area, four distinct seasons, rainy and humid areas, coastal areas, and the matching primer, material, epoxy iron of the same type of topcoat epoxy zinc-rich coating Primer epoxy rich paint inorganic zinc rich red paint, epoxy iron material, epoxy rich red paint zinc paint, epoxy iron red paint epoxy mica coating intermediate paint, epoxy glass flake paint material, alkyd paint , Chlorosulfonated Polyethylene Fluorocarbon Coatings, Chlorosulfonated Polyethylene Coatings, Polychlorinated Rubber Coatings, Polyurethane Coatings, Polyurethane Coatings, Vinyl Coated Urethane Coatings, Acrylic Polyurethane Materials, Polyurethane Acrylic Polyurethane Coatings, Chlorine Coating ester coating rubber coating heat insulation function
.
Exposure to the sun will cause the temperature of the storage medium in the oil tank to rise and accelerate the volatilization of the oil, which causes waste and pollutes the environment.
Therefore, paints with good thermal insulation properties should be selected
.
Research and practice have shown that white has a significant function of reflecting solar radiant heat.
According to information, in Europe, white protective coatings will be mandatory for volatile oil tanks.
Therefore, white or nearly white anticorrosive coatings should be selected for product oil tanks.

.
However, there are also some thermal insulation coatings with thermal insulation function.
The coating has more pores.
Once it leaks, it will cause water to penetrate.
Because the immersed water is difficult to volatilize and reduce the protective effect, you should be cautious when choosing this type of coating
.

2.
4 Stain resistance
.

The construction of modern tank farms usually requires reasonable planning to meet many humanistic requirements such as coordination with the surrounding environment and highlighting the characteristics of the enterprise.
Therefore, whether the tank wall anticorrosive coating can be kept clean and beautiful is getting more and more attention
.
Generally, a smooth and dense coating has good pollution resistance, but due to different formulations, even the same type of film-forming base material has a great difference in pollution resistance
.
Therefore, when choosing a coating, the stain resistance index and stain resistance (white or light color) of the coating should be investigated! At present, among the anticorrosive coatings for the outer wall of oil tanks, fluorocarbon coatings give the coating a lower friction coefficient due to the high bond energy CF bond in its molecular structure, so that the coating has good stain resistance; high crosslinking density The pollution resistance of polyurethane coatings is also better
.

2.
5 Good recoatability
.

When considering the needs of refurbishment and maintenance of oil tanks, anticorrosive coatings with good recoatability should be selected, such as one-component self-drying coatings such as chlorinated rubber, ethylene, and chlorosulfonated polyethylene
.

Special features
.
Some oil tanks are built in special environments, such as in damp caves, with poor air circulation and high humidity.
When choosing anti-corrosion coatings for the outer wall of such oil tanks, you should choose solvent-free or high-solid type and can be used on wet surfaces.
Cured anticorrosive coating
.
For oil tanks built in desert areas, anti-corrosion coatings with good abrasion resistance and impact resistance should be selected.
In addition, the field test data of the selected coatings in the desert environment should be investigated
.

Third, the choice of anti-corrosion paint for the inner wall of the oil tank

In the medium in contact with the inner wall of the oil tank, the composition of the refined oil is relatively stable, and the composition of crude oil, residual oil, and slop oil is quite different.
Therefore, when choosing an anticorrosive coating for the inner wall of an oil tank, in addition to considering the following aspects, you should also Do soak tests for special ingredients in oil to ensure good results
.

3.
1 Oil resistance
.

Organic anticorrosive coatings in oil products, especially in the immersion of light oil, are prone to swelling, and even leaching of pigments and fillers or coating softening and peeling, which will pollute the oil and seriously affect the quality of the oil
.
The oil resistance of inorganic coatings is better than that of organic coatings, but the chemical resistance is poor, and they are generally not directly exposed to environments with complex chemical factors
.
Practice has shown that epoxy and polyurethane anti-corrosion coatings commonly used on the inner wall of oil tanks are not in all kinds of anti-corrosion coatings because of the close molecular structure after cross-linking; House.
Allrightsreserved, http:// is only oil-resistant The performance is good, and the resistance to chemical media (such as acid, alkali, salt) is also very good, so it is suitable for anti-corrosion coatings for the inner wall of oil tanks
.

3.
2 Conductivity of static electricity
.

Liquid petroleum products will generate static charges during dynamic processes such as production and transportation, and the accumulated charges will cause explosion hazards when they are discharged.
Therefore, anti-static measures should be taken for oil production, storage and transportation facilities, pipelines, and refueling auxiliary tools
.
GB13348 "Static Safety Regulations for Liquid Petroleum Products" 52 stipulates that the inner wall of the storage tank should use anti-static paint, and the volume resistivity of the paint should be less than 108! (M.
When choosing anti-corrosion coatings for the inner wall of oil tanks, you must choose anti-corrosion coatings with electrostatic conductivity (the volume resistivity of the coating should be less than 108! (m).
The anti-corrosion coating's anti
-static function is often through the addition of graphite to the coating.
Powder, carbon black, metal powder and organic carbon fiber powder and other fillers.
It can be
used in storage tanks of jet fuel, lamp kerosene, light diesel, naphtha, light solvent oil, gasoline and other oil products with a flash point of less than 60.
In general, anti-static coatings with aluminum powder are generally not selected, because metallic aluminum increases the risk of sparks
.

3.
3 High temperature resistance
.

The anti-corrosion paint used on the inner wall of the oil tank should be able to withstand high temperatures of 120-150°C in the short-term to meet the requirements of steam cleaning method; it can withstand the medium temperature of 50° in the long-term to meet the requirements of heating and storage of certain oil products
.
The temperature resistance of commonly used epoxy and polyurethane anti-corrosion coatings meets the above requirements
.

3.
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Control the roughness of the substrate surface
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In the coating construction technical requirements, generally only the grade of rust removal is required, and the surface roughness of the substrate after rust removal is not specified, but the effect of roughness on the coating quality cannot be ignored
.
Roughness is too large, which will result in many leaks after painting and seriously affect the quality of anti-corrosion.
A suitable roughness is about 1/3 of the dry film thickness of the coating film.
For example, the dry film thickness of the primer is 60 "m, and the roughness should be controlled.
20-30 "m is ideal
.
In the actual rust removal construction, the anchor pattern depth of the substrate surface can be measured by the anchor pattern paper method or roughness meter, and the appropriate roughness can be obtained by adjusting the particle size, shape, and hardness of the abrasive used for jet rust removal
.

Pay attention to weather changes and arrange the coating construction reasonably
.
The anti-corrosion of oil tank is an outdoor construction.
It is necessary to know the weather in advance when painting, and try to avoid the corrosion of rain, dew, sand, etc.
when the coating film is not fully cured, so as to ensure a good anti-corrosion effect
.

Five, concluding remarks

Choosing suitable anti-corrosion coatings is a prerequisite for ensuring the anti-corrosion quality of oil tanks
.
Applicable anti-corrosion coatings should not only meet the design requirements for anti-corrosion performance, but also require that the construction performance is suitable for the on-site conditions of oil tank construction and the process conditions of anti-corrosion construction
.
Therefore, when choosing anti-corrosion coatings, we must first analyze the external environment where the oil tank is built and the composition of the medium to be stored, and then select an anti-corrosion coating that not only meets the anti-corrosion requirements, but also has construction applicability according to the on-site construction environment and process
.