Cryogenic Ball Valves

Cryogenic ball valves are a crucial component in various industries that deal with extreme temperatures. These cryogenic valves are specifically designed to withstand the low temperatures encountered in cryogenic applications, making them indispensable in fields such as oil and gas, aerospace, and medical research. One of the key features of cryogenic ball valves is their ability to maintain a good seal even at extremely low temperatures. This is achieved through the use of specialized materials such as stainless steel or brass, which can withstand the thermal stresses associated with cryogenic conditions. Additionally, these valves are equipped with extended bonnets that provide extra insulation to prevent freezing and ensure smooth operation. Another important aspect of cryogenic ball valves is their reliability. These valves are designed to handle high-pressure applications while maintaining excellent flow control capabilities. The spherical design of the valve allows for easy opening and closing, reducing friction and wear on the sealing surfaces. Furthermore, cryogenic ball valves offer versatility in terms of installation options. They can be installed horizontally or vertically depending on the specific requirements of the application. This flexibility makes them suitable for a wide range of industries where space constraints may exist.
 
At present, cryogenic ball valves are commonly used in LNG receiving stations. The number of cryogenic ball valves accounts for 80% of the number of valves in the entire LNG receiving station. Internal leakages of cryogenic ball valves occur during use.
 
Design guidelines for cryogenic ball valves
The design and manufacturing of cryogenic ball valves face a series of technical problems, such as material selection, low-temperature sealing, structural design, solid solution treatment, cryogenic treatment, thermal insulation, quality inspection, maintenance and safety due to the extremely low operating temperature. For this reason, there are a series of strict standards for the design of cryogenic valves. Internationally, the main standards used are BS 6364 "Cryogenic Valves" and MSS SP-134 "Requirements for Cryogenic Valves and Their Valve Bodies or Bonnet Extensions". These two standards relatively comprehensively stipulate the key points and rules for the design and manufacture of cryogenic valves. When designing cryogenic valves, in addition to following general valve design principles, special requirements for cryogenic valve design should be followed based on the conditions of use.
 
① Valves should not become a significant heat source for cryogenic systems. This is because the inflow of heat not only reduces the thermal efficiency but also causes the internal fluid to evaporate rapidly if it is too much, resulting in abnormal pressure increase and causing danger.
② Low-temperature medium should not hurt the operation of the handwheel and the sealing of the packing.
③ Valve assemblies that are in direct contact with low-temperature media should have explosion-proof and fire-proof structures.
④ Valve assemblies operating at low temperatures cannot be lubricated, so structural measures need to be taken to prevent friction parts from being scratched.
 
In the design process of cryogenic valves, in addition to considering the general requirements such as the flow capacity of cryogenic valves, some other indicators also need to be considered to better evaluate the technical level of cryogenic valves. The technical level of cryogenic valves is usually evaluated by measuring whether the energy consumption is reasonable.
 
① Thermal insulation of cryogenic valves
② Cooling of cryogenic valves
③ The working performance of opening and closing seals of cryogenic valves.
④ Not freezing for the surface of the cryogenic valve
 
The working environment of cryogenic valves is very different from that of general valves. In the process of designing, manufacturing and inspecting cryogenic valves, in addition to complying with the general rules for valve design, manufacturing and inspection, we should also pay attention to the environment in which cryogenic valves are located and make appropriate adjustments.
 
Basic theory
The factors that affect the valve’s sealing mainly include the structure of the sealing pair, the specific pressure of the sealing surface, the physical properties of the medium and the quality of the sealing pair. However, only by truly understanding the valve sealing principle and fully considering various factors that affect its sealing can we prevent leakages and ensure sealing.
 
Taking plane sealing as an example, we study the sealing of sealing surface connections and briefly explain the sealing principle. The principle of sealing is shown in Figure 1. The container is filled with liquid and gas with a certain pressure and sealed with a cover. The static pressure of the medium in the container is: FJ=A×P
 
In the formula, FJ is the media force.
A is the area of medium acting on the cover plate.
P is the static pressure of the medium in the container.
 
To keep the cover in the position shown in the figure, an external force F equal to FJ must be applied in the vertical direction of the contact surface between the container and the cover, which can only ensure end-face fit. Only when the sealing surface is an ideal plane, the medium will not pass between the joint surfaces. To ensure the sealing of the contact surface, an interaction force must be generated between the sealing surfaces, that is, the cover plate must be pressed well against the container. When the acting force F is greater than FJ, a certain specific pressure will be generated on the combined sealing surface, and the existing flatness on the plane will be deformed depending on the specific pressure. If the deformation is within the elastic limit of the material and produces little residual deformation, and the sealing property can be guaranteed when a force F is applied to the contact surface. In addition to the sealing-specific pressure, factors to ensure the sealing of the connection also include the sealing structure and others. However, among this series of factors, the specific pressure value between the sealing surfaces plays a key role.