Views: 0 Author: Site Editor Publish Time: 2025-08-12 Origin: Site
In the field of transportation and control of cryogenic media such as liquefied natural gas (LNG), liquid oxygen, and liquid nitrogen, ultra-low temperature trunnion ball valves have broad application prospects. Under cryogenic working conditions, such valves not only need to have reliable sealing performance but also meet multiple safety performance indicators such as resistance to low-temperature brittleness, anti-static properties, and fire resistance. Therefore, the scientific selection of materials and systematic optimization of structural design are the core elements to ensure the stable operation of ultra-low temperature trunnion ball valves.
(I) Valve Body and Bonnet Materials
As the core components of ultra-low temperature trunnion ball valves, the material selection of the valve body and bonnet directly affects the strength and low-temperature resistance of the valve. Currently, the mainstream application materials include:
austenitic stainless steel (such as 304L, 316L): which exhibits excellent toughness and brittleness resistance in low-temperature environments, and can withstand extreme temperature fluctuations without brittle fracture.
nickel-based alloys (such as Inconel 625): which are suitable for lower temperature ranges and have higher strength levels and corrosion resistance.
(II) Valve Seat Sealing Materials
The selection of valve seat sealing materials has a decisive impact on the sealing performance of ultra-low temperature trunnion ball valves. Commonly used sealing materials mainly include:
polytetrafluoroethylene (PTFE): whose applicable temperature range is -196°C to 200°C, with excellent low-temperature resistance and self-lubricating properties.
polychlorotrifluoroethylene (PCTFE): which has better strength and hardness than PTFE, and its applicable temperature range is -196°C to 150°C.
Valve Stem Sealing Materials: Valve stem sealing usually uses flexible graphite packing or lip seals, which can maintain a good sealing state under low-temperature conditions.
Other Key Components
The valve stem is generally made of high-strength stainless steel or nickel-based alloy, because it can maintain stable mechanical properties and fatigue resistance in low-temperature environments.
The materials of bolts and nuts need to match the materials of the valve body and bonnet to ensure the stability of the overall structure.
II. Key Points of Structural Design
(I) Valve Stem Area Design
Extended Valve Stem Structure: To prevent the packing from losing elasticity in low-temperature environments, ultra-low temperature trunnion ball valves usually adopt an extended valve stem structure. This structure can keep the stuffing box away from the valve body, ensuring that the temperature in the stuffing box area remains above 0°C, thereby extending the service life of the packing and reducing cold loss.
V-type Packing Seal: Different from the O-rings commonly used in normal temperature ball valves, the valve stem seal of ultra-low temperature ball valves should adopt V-type packing. The V-type packing adjusts the initial compression amount through a pressure ring, which can achieve a good sealing effect under low-pressure working conditions, and its sealing performance can be further enhanced as the medium pressure increases.
(II) Valve Seat Area Design
Valve Seat Sealing Ring: The valve seat sealing ring is one of the main leakage risk points of ultra-low temperature trunnion ball valves. To improve the sealing performance, the valve seat sealing ring is usually made of PTFE or PCTFE materials. At the same time, through accurate calculation of the sealing specific pressure, the angle, width of the sealing surface and the position of the sealing point are optimized to ensure the sealing efficiency.
LipSeal Gasket: The connection part between the valve seat and the valve bonnet seat cavity should adopt a LipSeal gasket. This gasket is a spring-energized sealing device with a PTFE jacket, which can maintain excellent sealing performance in low-temperature environments, and as the pressure increases, the sealing lip can fit more closely to the sealing groove.
(III) Fire and Anti-static Design
Fireproof Structure: Ultra-low temperature trunnion ball valves need to be equipped with a fireproof structure to prevent medium leakage caused by the melting failure of the sealing ring in case of fire. A typical fireproof structure adopts a double sealing design of graphite wound gaskets and lip seals to ensure that the sealing state can still be maintained under fire conditions.
Anti-static Device: Under low-temperature working conditions, anti-static devices should be installed at the junction of the valve stem and the ball, and at the contact between the valve stem and the bonnet to avoid static accumulation. Such devices usually adopt a steel ball and spring structure to ensure permanent conduction between various components and the valve body.
(IV) Self-relief Design
The volume of most cryogenic media will expand significantly after vaporization. For example, the volume of liquefied natural gas after vaporization is more than 600 times that of the liquid state. Therefore, ultra-low temperature trunnion ball valves need to be designed with a self-relief structure to prevent valve damage caused by abnormal pressure increase in the valve cavity.
(V) Deep Cold Treatment
Key components of ultra-low temperature trunnion ball valves (such as valve body, bonnet, ball, valve seat, etc.) need to undergo deep cold treatment. Deep cold treatment can release the internal stress of the parts and ensure the dimensional stability and service performance of the parts in low-temperature environments.
