DMS SEALS TECHNOLOGY CO.,LIMITED
DMS Seals-Mechanical Seals and Oil Ring Seals Manufacturer
The Professional Sealing Solution Supplier(O Ring Suppliers & Oil Seal Manufacturers).
The seal ring for special ultra-low temperature special valve is suitable for the valve with medium temperature of -40℃～-196℃, which is called low temperature valve. The low temperature valve includes low temperature ball valve, low temperature gate valve, low temperature globe valve, low temperature safety valve and low temperature check valve. , Low temperature butterfly valve, low temperature needle valve, low temperature throttle valve, low temperature pressure reducing valve, etc.
Mainly used in ethylene, liquefied natural gas installations, natural gas LPG LNG storage tanks, receiving bases and satellite stations, air separation equipment, petrochemical exhaust gas separation equipment, liquid oxygen, liquid nitrogen, liquid argon, carbon dioxide cryogenic storage tanks and tankers, transformers Adsorption oxygen and other devices. The output liquid low-temperature media such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc., are not only flammable and explosive, but also gasify when heating up, and the volume expands hundreds of times when gasified. The material of the LNG valve is very important. If the material is not qualified, it will cause external leakage or internal leakage of the casing and sealing surface; the comprehensive mechanical properties, strength and rigidity of the parts cannot meet the requirements of use or even break. Leakage of liquefied natural gas medium causes explosion.
Therefore, in the process of developing, designing and developing LNG valves, the material is the primary and key issue. After many years of manufacturing, it has accumulated rich experience, from design, technology to manufacturing, it has become more and more mature, and has developed a series of low-temperature valve products.
1. Product specifications and design parameters of cryogenic valves:
（1） Pressure class: 150, 300, 600Lb, 900LB, 1500LB (45MPa)
（2） Valve diameter: 15～1200 mm (1/2～48").
（3） Connection type: flange type, welding type, thread.
（4）Valve material: LCB, LC3, CF8.
（5） Working temperature: -46℃ , -101℃, -196℃, -253℃
（6） Applicable medium: liquefied natural gas, ethylene, propylene, etc.
（7） Drive mode: manual, bevel gear drive, electric.
2. the low temperature valve standard and product structure:
（1）Design: API6D, JB/T7749
（2） Valve routine inspection and test: according to API598 standard.
（3）Valve low temperature inspection and test: according to JB/T7749.
（4） Drive mode: manual, bevel gear drive and electric drive.
（5） Valve seat form: The valve seat adopts a welded structure, and the sealing surface is surfacing with cobalt-based hard alloy to ensure the sealing performance of the valve.
（6） The gate adopts an elastic structure, and a pressure relief hole is designed at the pressure inlet end.
（7） The valve body with one-way seal is marked with the flow direction mark.
（8） Low temperature ball valve, gate valve, globe valve, butterfly valve adopt long neck structure to protect packing.
（9）Ultra-low temperature ball valve standard: JB/T8861-2004
3. Cryogenic valve material selection:
(1) Valve body and bonnet adopt: LCB(-46℃), LC3(-101℃), CF8(304)(-196℃)
(2) Gate: stainless steel surfacing with cobalt-based cemented carbide
(3) Valve seat: stainless steel surfacing with cobalt-based cemented carbide
(4) Stem: 0Cr18Ni9
4. Manufacturing and testing of cryogenic valves:
Strict manufacturing process and special equipment are used for the cryogenic valves produced, and strict quality control is carried out on the processing of parts. After special low temperature treatment, the rough machined parts are placed in the cooling medium for several hours (2-6 hours) to release the stress, ensure the low temperature performance of the material, and ensure the finishing size to prevent the valve from being damaged due to low temperature conditions. Leaks caused by deformation due to temperature changes. The assembly of the valve is also different from that of ordinary valves, and the parts need to be strictly cleaned to remove any oil stains to ensure the performance.
5. Low temperature valve test equipment:
(1) Low temperature valve test device
(2) Liquid nitrogen storage device
(3) Low temperature treatment tank
(4) Low temperature test bench to ensure the performance of the valve under low temperature conditions
6. Low temperature valve test and inspection: The main parts of the low temperature valve are treated at low temperature and each batch is sampled for low temperature impact test to ensure that the valve is not brittle under low temperature conditions and can withstand the impact of low temperature media.
The following tests are performed on each valve:
Normal temperature shell strength test;
(2) Sealing test at normal temperature and low pressure;
(3) Normal temperature and low pressure sealing test;
(4) Low temperature upper sealing air tightness test (when there is upper sealing);
(5) Low-temperature gas sealing test, etc., to ensure that the entire low-temperature valve meets the requirements of the standard;
(6) Perform low temperature treatment on the main parts of the low temperature valve and perform low temperature impact test on each batch of samples to ensure that the valve is not brittle under low temperature conditions and can withstand the impact of low temperature media;
Other parameters of cryogenic valve: light body and small size. In order to reduce the heat loss of the valve body, especially to ensure the use of the valve under ultra-low temperature, the valve body is specially designed to be light in weight and small in size. The long-shaft valve, the valve through which the low-temperature fluid flows, adopts the form of a long valve stem, which can avoid the effect of external heat and keep the gland at normal temperature, so as to prevent the performance of the cover seal from being degraded.
This length is the optimum length obtained by calculation and experimentation. →Ideal valve seat soft sealing structure: In SW and BW forms, the valve body cannot be removed from the piping. In order not to replace the valve body, the valve seat adopts a soft contact valve seat. The valve core seal is made of Teflon containing 15% glass fiber with good low temperature characteristics and stability, and can be replaced according to needs.
Hard metal seal structure: metal seals are used on gate valves and valves with fire protection requirements. It is to add a stellite metal bushing to the contact surface of the valve seat to improve the surface hardness and improve the anti-burn and wear resistance. The gasification and boosting structure gate valve adopts a flexible structure and is completely sealed.
Therefore, at this time, the liquefied gas inside the valve body is sealed, and when the temperature rises after absorbing external heat, the phenomenon of regasification will occur, causing the internal pressure of the valve to increase. In order to prevent this phenomenon, a structure in which a decompression hole is opened in the valve body is adopted. The gland packing with excellent durability adopts Teflon ring packing with excellent durability in the gland part. This packing can rely on internal pressure to have self-pressure sealing performance, so it can be easily controlled with a small tightening torque, and the friction force is small, so it is easy to operate. Gasket, gasket is made of Teflon material containing ceramic filler material with stable sealing performance.
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