Cryogenic Butterfly Valve

◆ Cryogenic butterfly valve is a common valve that works in low temperature medium. NEWLOTOKE solves the problem of thermal expansion and contraction of the valve in a low temperature environment by improving the process and sealing structure. The common low temperature medium includes: the temperature of liquefied ammonia is -269℃, The temperature of hydrogen is -254 ℃, the temperature of liquefied helium is -196 ℃, the temperature of liquid oxygen is -183 ℃, and the temperature of liquefied natural gas is -162 ℃. These media output liquid cryogenic 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 the temperature rises, and the volume expands hundreds of times during gasification.

◆ Cryogenic valves have harsh working conditions. Most of their working media are flammable, explosive, and highly permeable substances. The minimum working temperature can reach -269℃, and the maximum working pressure can reach 10MPa. Therefore, the design, manufacture, and inspection of cryogenic valves are quite different from those of general purpose valves. Therefore, we adopt low-temperature resistant metal-to-metal structure, multi-eccentric frictionless patented design, excellent low-temperature test, and excellent technology to make the seals expand and contract uniformly to ensure the temperature and service life of the valve.

Generally, according to the operating conditions of cryogenic valves, the following requirements are put forward for the design work:

◆ The valve and its components should have the ability to work for a long time under the low temperature medium and the ambient temperature (usually 10 years or 35000~50000 cycles);

◆ Compared with the low temperature medium, the valve should not become a significant heat source. This is because the inflow of heat will reduce the thermal efficiency, and too much heat inflow may also vaporize the low temperature medium inside the valve, causing abnormal pressure rise and causing danger;

◆ The low temperature medium should not have a harmful effect on the operation performance of the hand wheel and the sealing performance of the packing;

◆ The structure of the valve assembly directly in contact with the cryogenic medium should meet the relevant explosion-proof and fire-proof requirements;

◆ The valve assembly working at low temperature cannot be lubricated, so measures need to be taken to prevent the friction parts from being scratched.

◆ Low temperature treatment of valve body and all parts: it can fully withstand the expansion and contraction caused by temperature changes. Moreover, the structure of the valve seat will not be permanently deformed due to temperature changes.

◆ Adopting a long-necked bonnet structure: The neck length of the valve cover is determined according to BS 6364 or MSS SP-134; this method has been verified by finite element analysis according to tests or user requirements.

lengthening the neck. Its purpose is to protect the stuffing box. Because the tightness of the stuffing box is one of the keys to cryogenic valves. If there is a leak in this area, it will reduce the cooling effect and cause the liquefied gas to vaporize. This is because as the temperature decreases at low temperatures, the elasticity of the packing gradually disappears, and the anti-leakage performance decreases. Due to the infiltration of the medium, the packing and the valve freeze, which affects the normal operation of the valve stem, and the valve stem moves up and down. The packing is scratched, causing serious leakage. Therefore, the cryogenic valve must adopt a long-necked valve cover structure. In addition, the long neck structure is also convenient to wind the cold insulation material to prevent cold energy damage

◆ The neck length L of the long neck valve cover (see Figure 1) is determined according to factors such as the thermal conductivity of the material, the thermal conductivity area and the surface heat dissipation coefficient. At the same time, it satisfies the need of cold insulation thickness. The neck length can be obtained by the test method. Table 1 is the neck length of the long neck valve cover designed in consideration of the standard cryogenic valve operating temperature and the thickness of the cold insulation material.

◆ With a manhole design, quick disassembly and assembly of the valve seat and disc seal assembly for online maintenance, the Newlotoke butterfly valve can be disassembled and reassembled without special tools.

◆ The replaceable valve seat and seal ring design will not cause the whole machine to report fees due to seal wear and reduce the use cost;

◆ The valve seat and sealing ring adopt a multi-eccentric frictionless structure and STL sealing surface: the multi-eccentric design makes the thermal expansion and cold contraction of the sealing ring more uniform, the seal is more stable, and the life is longer. The closing part of the cryogenic valve adopts STL sealing surface. The soft sealing structure is only suitable for cryogenic valves whose temperature is higher than -70℃ because of the large expansion coefficient of PTFE and brittleness at low temperature. Polytrifluoroethylene can be used for cryogenic valves at -162°C.

◆ Upper sealing seat structure, upper stem spline without pin anti-blow out structure,The dual valve stem design solves the problem of inconsistent expansion of the valve stem, butterfly plate, and valve body due to thermal expansion and contraction.The lower valve stem adopts a fixed shaft for better rigidity, which can shorten the connection position of the valve stem inserted into the butterfly plate, and make the channel flow resistance smaller

◆ The valve plate has small flow resistance, reducing energy consumption

◆ Material selection of fasteners

When the temperature is higher than -100°C, the bolt material shall be Ni, Cr-Mo and other alloy steel, which shall be properly heat-treated to improve the tensile strength and prevent thread bite. In order to prevent the nut and bolt from seizing, the nut is generally made of Mo steel or Ni steel, and the surface of the thread is coated with molybdenum disulfide.

◆ Selection of gaskets and packing materials for cryogenic valves

As the temperature decreases, the fluoroplastic shrinks greatly, which will reduce the sealing performance and easily cause leakage. Asbestos filler cannot avoid penetration and leakage. Rubber has swelling properties to natural gas and cannot be used at low temperatures. In the design of cryogenic valves, on the one hand, the structural design ensures that the packing is close to the ambient temperature. For example, the long-neck bonnet structure is adopted to keep the stuffing box as far away from the low-temperature medium as possible. On the other hand, consider when choosing packing Low temperature characteristics of the filler. Cryogenic valves generally use flexible graphite packing.

Flexible graphite is an excellent sealing material. This material is impermeable to gas and liquid, and has 10% to 15% elasticity in the thickness direction, and sealing can be achieved with lower fastener pressure. It is self-lubricating and can be used as valve packing to prevent the packing and valve from wearing. The use temperature of flexible graphite is generally -200~870℃.

◆ The packing box cannot be in direct contact with low temperature, but is designed at the top of the long-necked valve cover, so that the stuffing box is located far away from the low temperature and works in a temperature environment above 0℃. In this way, the sealing effect of the stuffing box is improved. In the event of leakage, or when the low-temperature fluid directly contacts the packing and the sealing effect decreases, grease can be added from the middle of the stuffing box to form an oil seal layer to reduce the pressure difference of the stuffing box as an auxiliary sealing measure. The stuffing box mostly adopts a two-stage packing structure with a middle metal spacer ring. However, other types such as the general valve stuffing box structure and the double stuffing box structure with the valve stem capable of being self-tightened are also used.

◆ The gasket is made of stainless steel wound flexible graphite gasket.

◆ The drip plate is a circular plate welded to the long neck part under the stuffing box to keep cold. Its main function is to prevent the moisture in the environment from flowing into the insulation layer directly after being cold into water and freezing. The diameter of the drip pan exceeds the diameter of the middle flange to prevent low-temperature condensed water vapor from dripping on the middle flange and bolts, causing heat loss and corrosion, affecting online maintenance.

◆ Metal seal, fireproof design

◆ Design standards：Meets API609, ASME B16.34, ASME VI, BS6364, DIN3840 requirements

◆ Connection standard：Meets ASME B16.10, IS05752 requirements

◆ Microleak test：Meets IS015848, API622, SHELL SPE77-312, TA-LUFT requirements

◆ Fire test：Meets API607, BS6755, ISO/FDIS10497 requirements

◆ Strength and sealing test standards：Meets API598, BS6364, EN12266\ISO5208 requirements

◆ Size: 3”~48”(DN80~DN2000)

◆ Class: 150LB ~ 900LB / PN6 ~ PN160

◆ Connection: Double flange long pattern / Double flange short pattern / Butt weld ·

Operation: Worm Gear / Pneumatic actuator / Electric actuator

◆ Temperature:-269℃~ -40℃

◆ Application:The temperature of liquefied ammonia is -269°C, the temperature of liquid hydrogen is -254°C, the temperature of liquefied helium is -196°C, the temperature of liquid oxygen is -183°C, the temperature of liquefied natural gas is -162°C

◆ Body: SS304L, SS316L, F316, LC1, LC2, LC3, LCB, WCB

◆ DiSC：CF3M,CF8M

◆ Stem: ASTM A479 XM-19(UNS S20910)

◆ Disc Sealing: F316L+STL

◆ Body Seat: F316L+STL

◆ In the design of ultra-low temperature valves, first consider that the main components of the valve should be able to withstand long-lasting or instantaneous large temperature changes and the thermal stress caused by the material capacity is the main factor to consider, under various loads under alternating pressure and temperature. In addition to regular strength calculations for valve bodies, bonnets, and stems, finite element stress analysis and seismic analysis should also be used to ensure the reliability of valve products. All the above-mentioned LNG cryogenic valves are made of low-carbon or ultra-low-carbon austenitic stainless steel as the main material, and its strength, toughness, temperature resistance, pressure resistance and erosion resistance are better than other materials.

◆ In order to prevent LNG from catching fire and explosion, the LNG system does not allow any leakage. LNG valves need to take very strict and effective measures to ensure the structural design, the selection of materials for the seals (packing, gaskets and sealing rings, etc.) and the quality inspection and control of the finished products. For this reason, we have conducted repeated low-temperature tests on various sealing structures and materials. The test method adopts the internationally common cold immersion method, that is, the whole test product is immersed in -196℃ low-temperature liquid nitrogen through helium inside the valve body The display instrument displays the helium leakage when the test temperature reaches -196℃. After testing the structure scheme and sealing material,

Finally determine the preferred structure and material. For this reason, the LNG cryogenic valve we produce has zero internal and external leakage and excellent performance. After testing, the valve meets the standard requirements. After high frequency and acceleration vibration test, the low temperature test is repeated to ensure its superior sealing and reliability.

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