Liquid oxygen, as a crucial industrial gas, has a wide range of applications in fields such as aerospace, medical, and chemical industries. However, storing liquid oxygen is not an easy task. It is an extremely low-temperature liquid, with a temperature as low as -183°C, and it also has strong oxidizing properties. This means that liquid oxygen storage tanks must not only have good sealing properties to prevent leakage and evaporation of liquid oxygen but also possess sufficient strength and low-temperature resistance to withstand the low temperature and pressure of liquid oxygen, while avoiding dangerous reactions with it. Therefore, the selection of materials and design of liquid oxygen storage tanks are of vital importance, directly relating to the safety, reliability, and economy of storage.
The strong oxidizing nature of liquid oxygen makes it prone to reacting with most substances. If the storage tank material cannot resist the corrosion of liquid oxygen, it may produce hazardous substances, and even lead to catastrophic consequences such as explosions or fires.
Stainless steel is a commonly used material for liquid oxygen storage tanks, known for its good corrosion resistance. However, it is important to note that the carbon content in stainless steel materials should not be too high. This is because, in a liquid oxygen environment, excessive carbon content may lead to the formation of explosive hydrocarbons. For example, when carbon comes into contact with liquid oxygen, under certain conditions, carbon can react with liquid oxygen to produce gases such as carbon monoxide and carbon dioxide. The accumulation of these gases may trigger an explosion. Therefore, when selecting stainless steel as the material for liquid oxygen storage tanks, it is essential to strictly control the carbon content. Generally, low-carbon stainless steel, such as austenitic stainless steel S30408, is chosen. This type of stainless steel has a low carbon content, which can effectively prevent the occurrence of the aforementioned dangerous situations.
Aluminum alloy also has good corrosion resistance and a certain degree of strength. In a liquid oxygen environment, a dense layer of aluminum oxide film forms on the surface of the aluminum alloy. This film can provide some protection under normal circumstances, but it also poses potential risks. If the aluminum oxide film is damaged or uneven, liquid oxygen may penetrate into the interior of the aluminum alloy, causing corrosion of the alloy and leading to tank leakage. Therefore, although aluminum alloy has some good performance characteristics, special attention must be paid to the integrity of its surface oxide film in the application of liquid oxygen storage tanks.
Titanium alloy is the best choice among materials for liquid oxygen storage tanks. It has high corrosion resistance and strength, and can well meet the safety requirements of the tank in a liquid oxygen environment. Unlike aluminum alloy, titanium alloy does not easily form a membrane that can cause leakage in liquid oxygen. It also does not produce dangerous hydrocarbons like high-carbon stainless steel. Titanium alloy can maintain stable performance in low-temperature environments, making it one of the ideal materials for liquid oxygen storage tanks.
The low-temperature characteristics of liquid oxygen make sealing a key factor in tank design. If the sealing is not tight, liquid oxygen will evaporate, not only causing waste of resources but also potentially bringing safety hazards.
Welding sealing is the most commonly used sealing method for liquid oxygen storage tanks at present. It achieves sealing by welding the seams of the tank. The development of welding technology has led to higher and higher quality of welding sealing. For example, the use of advanced welding equipment and techniques, such as automatic welding technology, during the welding process can effectively reduce welding defects such as porosity and slag inclusion. These welding defects may become channels for liquid oxygen leakage in low-temperature environments. Through strict quality control, welding-sealed tanks can effectively prevent the leakage of liquid oxygen.
Pressure sealing uses the internal pressure of the storage tank to maintain sealing. This method is suitable for some specific liquid oxygen storage tank structures. For example, by designing a reasonable pressure control system inside the tank and maintaining a certain pressure difference, liquid oxygen leakage can be prevented. However, pressure sealing requires higher strength and pressure resistance of the storage tank, as the tank needs to withstand a certain pressure to achieve sealing.
Packing sealing involves filling the seams of the storage tank with sealing materials to achieve sealing. The advantage of this sealing method is that appropriate sealing materials can be selected according to needs. For example, some sealants or gaskets with low-temperature and corrosion resistance can be used for packing sealing. However, the reliability of packing sealing is slightly lower than that of welding sealing, as the sealing materials may age or deform over time and due to temperature changes, leading to sealing failure. Therefore, when choosing packing sealing, it is necessary to regularly check the condition of the sealing materials and replace the aged ones in time.
Liquid oxygen storage tanks are containers that bear the pressure of liquid oxygen and extremely low temperatures, which means that the materials must have sufficient strength and low-temperature resistance.
Liquid oxygen storage tanks need to withstand the pressure of liquid oxygen, so the strength of the material is essential. Whether it is stainless steel, aluminum alloy, or titanium alloy, they all have a certain degree of strength. For example, the standard room temperature yield strength (or 0.2% specified plastic extension strength) of austenitic stainless steel S30408 should not exceed 460 MPa, and the upper limit of the standard tensile strength should not exceed 725 MPa. These strength indicators can ensure that the tank will not deform or rupture under normal working pressure. In the design of the storage tank, it is also necessary to carry out strength calculations and external pressure stability checks to ensure that the tank can work safely and reliably under various working conditions.
The temperature of liquid oxygen is extremely low, reaching -183°C. The storage tank material must maintain sufficient strength in this low-temperature environment to prevent brittle fracture caused by low temperature. Commonly used liquid oxygen storage tank materials such as stainless steel, aluminum alloy, and titanium alloy have all undergone strict low-temperature performance tests. For example, the outer shell steel plate should have good weldability, sufficient strength, and impact toughness, while also considering the corrosive effects of the external environment. When low-alloy steel steel plate is selected, it should comply with the provisions of GB/T 713 or GB/T 3531; when austenitic stainless steel steel plate is selected, it should comply with the provisions of GB/T 24511. These standards all have clear requirements for the low-temperature performance of the materials, ensuring that the materials will not break due to brittleness in low-temperature environments.
Liquid oxygen storage tanks are usually large-scale equipment with high manufacturing costs and long production cycles. Therefore, when selecting tank materials, the manufacturability and economy of the materials should be considered.
Common liquid oxygen storage tank materials such as stainless steel, aluminum alloy, and titanium alloy all have advantages in terms of processing performance. For example, stainless steel and aluminum alloy have good weldability, which makes welding operations convenient. Although titanium alloy has relatively greater welding difficulty, with the advancement of welding technology, its welding problems have also been well solved. At the same time, these materials also have good forming processing performance, which can meet the complex structural shape requirements of the storage tank. For example, the inner tank and outer shell of the liquid oxygen storage tank usually need to undergo processing techniques such as rolling and stamping, and these materials can adapt to these processing techniques to improve manufacturing efficiency.
In terms of economy, stainless steel, aluminum alloy, and titanium alloy also have their own characteristics. The price of stainless steel is relatively stable and widely used, with relatively low procurement costs. The advantage of aluminum alloy is its light weight, which can reduce the self-weight of the storage tank in some applications where the weight of the tank is a concern, such as in the aerospace field, thereby saving transportation costs. Although titanium alloy is relatively expensive, due to its excellent performance, it can reduce the amount of material used, while improving the safety and service life of the storage tank, and has good economy in some high-performance liquid oxygen storage tanks. When selecting materials, it is necessary to comprehensively consider factors such as the service life and maintenance costs of the storage tank to achieve the best economic effect.
The structural design of liquid oxygen storage tanks is also very important, as it relates to the overall performance of the tank.
Cryogenic containers should adopt a double-layer metal shell structure, with the cross-section of the inner container and the outer shell being circular. This structure can effectively reduce heat transfer and maintain the low-temperature state of liquid oxygen. The inner tank is made of austenitic stainless steel S30408, and the material of the outer container is selected according to the user's region, in accordance with national regulations, as Q235-B, Q245R, or Q345R. The interlayer between the inner and outer containers is filled with insulating material, such as perlite sand, and then evacuated. This type of insulation can further reduce heat transfer and improve the thermal insulation performance of the storage tank.
The structural design of liquid oxygen storage tanks should consider avoiding the accumulation of hydrocarbons. This is because hydrocarbons may cause dangerous reactions in a liquid oxygen environment. For example, when designing the inlet and outlet of the storage tank, it is necessary to avoid structures that may form dead ends or easily accumulate hydrocarbons. At the same time, regular cleaning and maintenance of the storage tank should be carried out to prevent the residual of hydrocarbons.
When carrying out strength calculations and external pressure stability checks on the tank, the design using rules should comply with the provisions of GB/T 150.3, and the design using analysis should comply with the provisions of JB 4732. During the design process, it is necessary to consider the loads caused by the temperature gradient between the inner container, interlayer piping, and outer shell during the manufacturing, testing, and normal working processes of cryogenic containers. For example, when the storage tank is heated and evacuated, the temperature change will cause the material to expand and contract, generating stress. If these stresses exceed the strength limit of the material, they may cause damage to the storage tank. Therefore, it is necessary to ensure that the storage tank can work safely and reliably under various working conditions through precise calculations and checks.
The material selection and design of liquid oxygen storage tanks is a complex system engineering task. In terms of corrosion resistance, stainless steel, aluminum alloy, and titanium alloy each have their advantages and disadvantages, and should be selected according to specific application scenarios. In terms of sealing, welding sealing, pressure sealing, and packing sealing each have their own characteristics, and the appropriate sealing method should be determined according to the structure and usage requirements of the storage tank. Strength and low-temperature resistance are essential properties that liquid oxygen storage tanks must possess, and these requirements can be met through reasonable material selection and structural design. At the same time, it is also necessary to consider the manufacturability and economy of the storage tank, to reduce manufacturing costs and improve service life while ensuring safety and performance. Through scientific and rational material selection and structural design, the safe, reliable, and economical operation of liquid oxygen storage tanks can be ensured, providing strong support for the storage and use of liquid oxygen.
