Application of metal seal butterfly valve in cryogenic equipment
With the rapid advancement of industrial technology, the valve industry has faced increasingly stringent requirements, especially for valves used in low-temperature environments. In particular, butterfly valves designed for cryogenic applications must not only meet general performance standards but also ensure reliable sealing at extremely low temperatures, maintain flexible operation, and satisfy other unique demands specific to cryogenic systems. As industrial technologies continue to evolve, the need for high-performance cryogenic valves is growing.
Butterfly valves are widely favored for their compact design, lightweight structure, and ease of operation. Compared to gate valves of the same diameter, they offer reduced fluid resistance (up to 40%–50% less) and quick opening and closing capabilities. However, in many domestic cryogenic devices such as natural gas liquefaction systems, air separation units, and pressure swing adsorption equipment, over 80% of the valves used are still gate valves, with very few butterfly valves in application. The primary reason for this is the poor low-temperature sealing performance of traditional metal-sealed butterfly valves, which can lead to leakage due to structural irregularities or material deformation under extreme cold conditions. This significantly affects the safety and operational stability of these low-temperature systems.
As the development of cryogenic equipment accelerates, the demand for more advanced cryogenic valves is increasing. To meet market needs, structural improvements have been made to metal-sealed butterfly valves. A high-eccentricity butterfly valve, which has already been patented, is now being developed to better suit both high and low-temperature applications. Here, we briefly introduce its low-temperature performance.
First, the sealing performance of low-temperature valves is critical. There are two main causes of leakage: internal leakage and external leakage. Internal leakage is primarily caused by the deformation of the seal pair due to low temperatures. When the temperature drops, materials may undergo phase changes, leading to volume expansion or contraction. This can warp the original precision of the sealing surfaces, resulting in poor sealing performance. For example, during a low-temperature test on a DN250 butterfly valve using liquid nitrogen (-196°C), the 1Cr18Ni9Ti valve disc showed a deformation of approximately 0.12 mm, which was the main cause of internal leakage.
To address this issue, a new butterfly valve design has been introduced, changing from a flat seal to a conical seal. The valve seat features an elliptical cone-shaped sealing surface, while the disc is equipped with a floating elastic seal ring. This ring can move radially within the disc groove. When the valve closes, the elastic seal first contacts the minor axis of the elliptical surface, then gradually moves toward the major axis, ensuring full contact with the entire sealing surface. This design allows the valve to compensate for any low-temperature deformation without causing leaks or jamming. When opened, the elastic seal returns to its original shape, minimizing friction and extending the valve’s service life.
Second, external leakage often occurs at the flange connection between the valve and the pipeline. At low temperatures, the mismatch in thermal contraction between the gasket, bolts, and pipe can lead to loosening and subsequent leakage. To prevent this, the connection method has been changed from flanged to welded structures, eliminating potential leakage points. Additionally, stem packing leakage is another common issue. While PTFE (F4) is widely used due to its self-lubricating properties and chemical stability, it tends to shrink at low temperatures, causing ice buildup and making the valve difficult to open. To solve this, a self-shrinking sealing structure has been developed, utilizing the high thermal expansion coefficient of PTFE to ensure tight sealing at both room and low temperatures.
Furthermore, the design of the valve body and stem bushing is crucial. The selection of appropriate materials ensures reliable operation under low-temperature conditions. Butterfly valves, due to their compact size and regular shape, have smaller heat capacity and lower cooling requirements, making them ideal for cryogenic applications. For example, the newly developed DD363H type butterfly valve is specifically designed for cryogenic use, with a shell material of 1Cr18Ni9Ti austenitic stainless steel, known for its excellent low-temperature performance.
In addition, the choice of stem bushings is important. Some cryogenic valves have experienced issues such as sticking or clogging due to improper material selection, insufficient cold clearance, or poor machining accuracy. To prevent these problems, self-lubricating composite bearings like SF-1 have been used on the upper and lower bushings of the stem, enhancing performance in extreme conditions.
Metal-sealed butterfly valves offer advantages that many conventional valves lack, such as low flow resistance, reliable sealing, quick operation, and long service life. The three-eccentric metal-sealed butterfly valve uses the deformation of an elastic ring to achieve sealing, eliminating the need for media force and enabling bidirectional sealing. With these benefits, butterfly valves are becoming increasingly popular in cryogenic applications.
In the future, we can expect to see more butterfly valves being used in low-temperature equipment, driven by continuous technological innovation and improved performance.
Polyamine Cas No. 39660-17-8,Polyamine For Paper Industry,Waste-Water Treatment Polyamine,Useful Polyamine
ZHEJIANG XINHAITIAN BIO-TECHNOLOGY CO.,LTD. , https://www.dadmacxht.com