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For low-temperature pressure vessels used as liquid nitrogen storage tanks, it takes 48 hours for evaporation to return to normal levels when filling them with liquid nitrogen; however, in the case of advanced liquid nitrogen storage tanks, this time can be reduced to 12 hours, with evaporation losses being reduced by 50%. Once we understand the properties of liquid nitrogen and the basic structure of liquid nitrogen storage tanks, we can use it accurately and fully leverage its capabilities. The key points for its use are outlined as follows: First, there must be a dedicated person responsible for handling, operating, and maintaining it. The storage area for liquid nitrogen tanks must have good air circulation. If multiple liquid nitrogen tanks are stored in a closed space, the evaporated nitrogen will remain inside, resulting in a lack of oxygen and potentially leading to asphyxiation. When handling liquid nitrogen storage tanks, it is necessary to handle them with care to prevent collisions with other objects. Since these tanks are in a state of high vacuum after evacuation, the pressure exerted by the atmosphere on their inner and outer surfaces is quite significant. Taking the DR-10 and DR-30 as examples, the pressure acting on the outer surface is approximately 4. . o kilograms to 9. . O kilograms; indeed, it can be made to have a strength three times that of its own weight, and careful handling is required to avoid losing it or causing it to collide with something. Employees working with Tianchi liquid nitrogen storage tanks are advised to ensure that the tanks are connected in a straight position; it is prohibited to pour the liquid nitrogen inside the tanks to prevent accidents. II. When filling liquid nitrogen for the first time, or when the interior of the liquid nitrogen storage tank is dry, an inspection must be conducted first to check whether there are any dents or other abnormal conditions on the outside of the tank. Check whether there are any foreign objects inside the tank, and ensure that the base is properly secured. When these environments are well-organized, liquid nitrogen can be started to be filled, and the process should be carried out in a place with good ventilation; generally, it can be done outdoors as well. If held indoors, doors and windows must be opened to ensure an excellent flow of air. One method of filling liquid nitrogen is the pressurized injection method, in which the liquid valve of a large liquid nitrogen container is opened, a flexible hose is connected, and liquid nitrogen is directly injected into the storage tank. Another method is to use the funnel pouring technique directly; it is particularly important to keep the end of the funnel slightly separated from the neck of the container, so that the vapor generated by the liquid nitrogen can escape smoothly through the gap between the funnel and the container. Otherwise, the liquid will overflow from the funnel, which not only increases the loss of liquid nitrogen but also leads to frostbite issues. The rate at which liquid nitrogen is filled should be slow; a small amount should be injected first, followed by a few minutes of pause to allow it to cool down, before gradually filling it to the specified volume. There are many ways to classify pressure vessels; from the perspectives of use, manufacturing, and inspection, the following classifications exist. (1) Classified by the level of pressure they are subjected to: low-pressure vessels, medium-pressure vessels, high-pressure vessels, and ultra-high-pressure vessels. (2) Classified by the medium contained: non-flammable, non-toxic ； Flammable or toxic ； Highly toxic. (3) Classified according to the different effects in the process: ① Reaction vessel: A vessel used to carry out physical and chemical reactions of the medium. ②Heat exchange vessel: A vessel used to facilitate the heat exchange between media. Industrial liquid nitrogen is obtained by compressing nitrogen at extremely low temperatures to turn it into a colorless liquid; at this point, the temperature of the liquid nitrogen is very low. It is then stored in steel cylinders, which are later placed in an environment at normal temperature. As the temperature of the surrounding environment rises, the liquid nitrogen contained within the cylinders undergoes a phase change, that is, it vaporizes, changing from a liquid state to a gaseous state. This causes the pressure inside the cylinders to increase. At this stage, the temperature remains such that both liquid and gas nitrogen coexist, typically at -196°C. As heat from the outside is absorbed and the temperature continues to rise, the pressure keeps increasing as well. In such cases, the pressure relief safety valve comes into action to release pressure. If pressure is not relieved and the temperature continues to rise, the pressure of the liquid nitrogen inside the cylinders can become extremely high, leading to the explosion of the pressure vessel.