tanks for compressed air

Figure 1: Air tanks.



Gas storage tanks, a kind of important special equipment, form a storage system for compressed air to reduce pressure fluctuations. An air tank’s design life is generally 10 years, but in the process of daily use, bad work environments, unqualified operations, or irregular maintenance could cause failures, shortening its service life.

Compressed air is the second-largest power energy after electricity. It has been applied in a wide range of scenes, such as electric power, spraying, food, metallurgy, petrochemical, automobile manufacturing, shipbuilding, precision electronics, chemical industry, printing.

In the compressed air system, the air is inhaled to the compressor through the air filter, compressed to reach the rated pressure, and transported to the gas storage tank through the exhaust pipe. The gas storage tank is used between the air compressor and the gas-burning equipment, which plays the role of reducing the pressure fluctuation of the compressed air system.

Air tanks reserve a certain amount of compressed air and maintain the balance between the air supply and demand. They can reduce the starting times of compressors. At the same time, the air storage tank will help compressed air stand for a period of time, effectively reduce the temperature, and release the pollutants and moisture in the air, improving the quality of the compressed air supply.

Seeing through the recent network media, we would figure out that accidents were due to the non-standard use of gas tanks and harsh environments. And design, manufacture, sales, installation, and use were not according to the requirements of special equipment. Users have selected cheap storage tanks that led to a series of safety accidents, causing air tanks to fail in the design service life cycle, enterprises to shut down, and a series of losses.

Therefore, more management departments at all levels, particularly the use and management departments of companies, have paid attention to effective management measures, standardized use, and extend the service life of gas tanks.

Factors Affecting Service Life of Air Tanks

an air tank used in the compressed air system

Figure 2: A compressed air system with a receiver tank.



As a general pressure vessel, because of different industries, its production of materials, the use of compressed air, and management methods are different. Generally, the pressure value inside the gas storage tank should not be larger than 1.6Mpa, the operating temperature should be less than 150°C, and the medium is compressed air or compressed nitrogen. During daily use, if the use of any link is not standard, the life of the air receiver will be seriously reduced.

Design Factors

Generally speaking, the higher the design pressure, the larger the storage capacity. The higher the design temperature, the greater the wall thickness of the material used in manufacturing. In addition, the welding coefficient, opening, nozzle, design corrosion allowance also affect the final wall thickness of the storage tank.

Excepting the defects of manufacturing materials and welding, the actual wall thickness directly affects the service life of tanks. Enterprises can take the wall thickness as the main reference data of the service life. If the operating environment does not meet the requirements of design conditions, such as excessive pressure and temperature, or harsh environmental conditions, it will seriously shorten the service life of the gas storage tank.

Material and Manufacturing Factors

The structure of an air receiver tank is composed of an upper and lower head and the middle circular cylinder. If the raw material steel body has defects or improper materials are used, which will cause uneven wall thickness, mechanical properties to be below the design value, material composition to be unqualified.

In the welding process, it is not strictly controlled and not properly selected to lead to slag inclusion, porosity, dark damage, and penetration of the welding seam, reducing the service life of the tank. Especially after using for some time, natural corrosion and rust will decrease the tank strength seriously, which cannot meet the requirements of safe use.



the structure of an air receiver tank is composed of an upper and lower head and the middle circular cylinder

Figure 3: An automotive air receiver tank.

Maintenance and Operation Factors

The use and maintenance of gas storage tanks are directly related to the service life, and the shortening of the life is largely related to the illegal operation and use. For example, there is no regular maintenance, no personnel, or personnel without training, safety accessories are not tested regularly, fail to clean the oil and water, excessive oil and water into the air tank, use environment of extremely low or high temperature, corrosive gases, all of which will shorten the service life of gas storage.

Main Measures and Methods for Extending Service Life of Gas Storage Tanks

When ordering, you should submit accurate design and use requirements information, so that the design of the gas storage tank will be consistent with the actual use of the site to avoid the service life reduction caused by design problems.

It’s strictly required that manufacturers should allow the relevant national standards and choose products from well-known brands to eradicate all kinds of defects in the production process, and strictly prohibit bumping and knocking the tank during transportation and installation.

The ambient temperature of the air tank should meet the design requirements. When it exceeds the design range, you should take measures to keep the tank warm or move it to the indoor light. The installation and use environment should meet the design requirements to avoid the corrosion of the gas storage tank wall caused by corrosive gases.

All kinds of safety accessories of gas storage tanks should be inspected regularly. When the gas storage tank is connected with other pipelines, the buffer bend pipe should be added to prevent fatigue damage or additional stress caused by the pipeline impact or vibration of the gas storage tank.

The gas storage tank should be regularly discharged and cleaned to avoid corrosion caused by water and oil pollutants. The oil and water removal equipment should be installed before the compressed air enters the gas storage tank to reduce the water causing corrosion of the tank wall.

You should report the use unit exceeding the design life to the testing institution and conduct regular inspection on the gas storage tank. When using and managing gas storage tanks, you shall comply with the relevant requirements. Training and educating operators regularly is necessary. They shall hold certificates and make records after using and maintaining the equipment.

Standards for Air Tanks

Air receiver tanks belong to pressure vessel that is special equipment. The following are three standards of pressure vessels.

Gases with the highest working pressure higher than or equal to 0.1Mpa (gauge pressure).

Liquefied gases and liquids are at the highest working temperature higher than or equal to the standard boiling point.

Containers are fixed and mobile of which volume larger than or equal to 30L and the inner diameter (the maximum geometric size of the inner boundary for non-circular section) longer than or equal to 150mm. Usually, we choose the gas storage tank concerning two parameters: design pressure (MPa) and volume (L or m3).

Summary

In recent, it is due to the use of air tanks without standard operations that have led to many accidents. It must be taken seriously by the users. Gas storage tanks are special equipment, and effective safety management measures and standard use for prolonging the service life have attracted all levels of departments. To a certain extent, better working environments and operations, scientific and reasonable maintenance can extend tanks’ service life.

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