Manufacturing, Installation & Causes of Leakages of Cryogenic Valves
In recent decades, with the development of modern science and technology, there has been an increasing demand for cryogenic valves in engineering projects. Cryogenic valves are widely used in fields such as fertilizer, LNG and petrochemical industries. Valves suitable for medium temperatures of -40°C to -250°C are called cryogenic valves. Cryogenic valves include cryogenic ball valves, cryogenic gate valves, cryogenic globe valves, cryogenic safety valves, cryogenic check valves, cryogenic butterfly valves and cryogenic needle valves. According to the characteristics of the medium and the requirements to adapt to the use of valves at low temperatures, the manufacturing and installation methods of cryogenic valves are different from ordinary valves.
Manufacturing
We have formulated strict manufacturing processes and used special equipment for the cryogenic valves we produce, and carried out strict quality control on the processing of parts. After special low-temperature treatment, the rough-machined parts are placed in the cooling medium for several hours (2 to 6 hours) to release stress, ensure the low-temperature performance of the material, and the finishing dimensions. This prevents the valve from deforming due to temperature changes and causing leakage when operating at low temperatures. The assembly of the valve is also different from ordinary valves. Parts need to be rigorously cleaned to remove any oil to ensure performance.
Installation
Because of the special structure of cryogenic valves, the installation of cryogenic valves also has its own special requirements. When installing cryogenic valves, the stem direction must be within an angle of 45 degree from being vertical to upward due to the structural characteristics of the long-neck bonnet of cryogenic valves, and installation on vertical pipelines should be avoided as much as possible. Otherwise, the low-temperature medium will fill the extended part of the valve bonnet, causing the valve packing to fail and transmit the cold energy to the valve handle, causing personal injury to the operator. For cryogenic valves with pressure relief structures, when installing the valve, special attention should be paid to the requirements for the pressure relief direction of the valve. The direction of valve pressure relief should be marked on the process flow diagram and reflected in the piping isometric drawing.
Reasons for leakages
1. Internal leakages: The main cause of internal leakages in valves is the deformation of the sealing pair at low temperatures. When the temperature of the medium drops to the point where the material undergoes a phase change, the volume changes, causing the sealing surface that was originally ground with high precision to warp and deform, resulting in poor low-temperature sealing.
2. Leakages of valves: First, when the valve and pipeline are connected by flanges, leakages occur due to the unsynchronized shrinkage of the connecting gaskets, connecting bolts, and connecting parts at low temperatures. Therefore, the connection method between the valve body and the pipeline can be changed from flange connection to welding structure to avoid low-temperature leakages. The second is the leakage at the valve stem and packing.
Manufacturing
We have formulated strict manufacturing processes and used special equipment for the cryogenic valves we produce, and carried out strict quality control on the processing of parts. After special low-temperature treatment, the rough-machined parts are placed in the cooling medium for several hours (2 to 6 hours) to release stress, ensure the low-temperature performance of the material, and the finishing dimensions. This prevents the valve from deforming due to temperature changes and causing leakage when operating at low temperatures. The assembly of the valve is also different from ordinary valves. Parts need to be rigorously cleaned to remove any oil to ensure performance.
Installation
Because of the special structure of cryogenic valves, the installation of cryogenic valves also has its own special requirements. When installing cryogenic valves, the stem direction must be within an angle of 45 degree from being vertical to upward due to the structural characteristics of the long-neck bonnet of cryogenic valves, and installation on vertical pipelines should be avoided as much as possible. Otherwise, the low-temperature medium will fill the extended part of the valve bonnet, causing the valve packing to fail and transmit the cold energy to the valve handle, causing personal injury to the operator. For cryogenic valves with pressure relief structures, when installing the valve, special attention should be paid to the requirements for the pressure relief direction of the valve. The direction of valve pressure relief should be marked on the process flow diagram and reflected in the piping isometric drawing.
Reasons for leakages
1. Internal leakages: The main cause of internal leakages in valves is the deformation of the sealing pair at low temperatures. When the temperature of the medium drops to the point where the material undergoes a phase change, the volume changes, causing the sealing surface that was originally ground with high precision to warp and deform, resulting in poor low-temperature sealing.
2. Leakages of valves: First, when the valve and pipeline are connected by flanges, leakages occur due to the unsynchronized shrinkage of the connecting gaskets, connecting bolts, and connecting parts at low temperatures. Therefore, the connection method between the valve body and the pipeline can be changed from flange connection to welding structure to avoid low-temperature leakages. The second is the leakage at the valve stem and packing.
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