Low temperature valve wall thickness, seat, anti-static design and manufacturing standards analysis low temperature valve application knowledge introduction

Low temperature valve wall thickness, seat, anti-static design and manufacturing standards analysis low temperature valve application knowledge introduction

Low temperature valve wall thickness, seat, anti-static design and manufacturing standards analysis
Suitable for medium temperature -40℃ ~ -196℃ valve is called low temperature valve. Cryogenic valves including low temperature ball valve, gate valve at low temperature, low temperature cut-off valve, safety valve, check valve at low temperature in low temperature, low temperature butterfly valve, needle valve at low temperature, low temperature throttle valve, cryogenic valve, etc., mainly used for ethylene, liquefied natural gas (LNG) plant, gas LPGLNG tank, accept base and goonhilly, air separation equipment, oil chemical tail gas separation equipment, Liquid oxygen, liquid nitrogen, liquid argon, carbon dioxide low temperature storage tank and tank truck, pressure swing adsorption oxygen production devices. The output liquid low-temperature medium such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc., is not only flammable and explosive, but also gasification when heating up. When gasification, the volume expands hundreds of times. Low temperature valve application, control the temperature, prevent, leakage and other hidden dangers.
Typical low temperature valve structure: commonly used low temperature valves are low temperature gate valve, low temperature globe valve, low temperature check valve, low temperature ball valve, low temperature butterfly valve and so on. Low temperature gate valve and low temperature ball valve in the chamber between the gate plate and the ball, are provided with a pressure relief hole. All cryogenic valves are unidirectional sealed AND have MEDIUM FLOW cast or MARKED ON the body.
1. Minimum wall thickness: the minimum thickness of the body and cover of the low temperature valve shell, does not accept the wall thickness in the ASMEB16.34 standard. The minimum wall thickness of gate valve shall not be less than API600, the minimum wall thickness of globe valve shall not be less than BS1873, the minimum wall thickness of check valve shall not be less than the minimum wall thickness of BS1868 and other standards; Stem diameter shall comply with API600 or BS1873 standards.
2. Valve seat: low temperature valve product sealing pair according to the working temperature and nominal pressure of the medium, can be designed as a metal-PTFE soft seal or metal-metal hard seal, but PTFE is only suitable for the working temperature of the medium is higher than 73℃, because too low temperature PTFE will become brittle. At the same time PTFE should not be used for pressure level greater than or equal to CL1500, because when the pressure exceeds CL1500, PTFE will produce cold flow, affecting the valve seal. The seat of hard sealed low temperature gate valve, check valve and globe valve adopts Co-Cr-W hard alloy surfacing directly on the valve body. Make the seat and the body as a whole, prevent leakage caused by the low temperature deformation of the seat, ensure the reliability of the seal between the seat and the body.
3. Anti-static: used for flammable and explosive low temperature medium, if the valve packing or gasket and seal for PTFE and other insulating materials, the valve open and close will produce static electricity, and static electricity for flammable and explosive low temperature medium is very terrible, so, the valve should be designed with anti-static device.
Low temperature valve material selection:
1. The valve body and cover adopt: LCB(-46℃), LC3(-101℃), CF8(304)(-196℃).
2. Gate: stainless steel surfacing cobalt-based hard alloy.
3. Seat: stainless steel surfacing cobalt-based carbide.
4. Stem: 0Cr18Ni9.
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: press JB/T7749.
4. Drive mode: manual, bevel gear drive and electric drive device.
5. Valve seat form: the valve seat adopts welding structure, and the sealing surface is surfacing cobalt-based carbide to ensure the sealing performance of the valve.
6. The ram adopts elastic structure, and the pressure relief hole is designed at the inlet end.
7. One-way sealed valve body is marked with flow direction mark.
8. Low temperature ball valve, gate valve, globe valve and butterfly valve adopt long neck structure to protect packing.
9. Temperature ball valve standard: JB/T8861-2004.
Low temperature valve application knowledge introduction
1. Low temperature application options
1. Operators use valves in cold environments, such as oil RIGS in polar seas.
2. Operators use valves to manage fluids at temperatures well below freezing.

Two, what affects valve design?
Temperature has an important effect on valve design. For example, a user might need it for a popular environment such as the Middle East. Or, it might work in cold environments like the polar oceans. Both conditions can affect valve tightness and durability. Components of these valves include the body, bonnet, stem, stem seal, ball valve, and seat. These components expand and contract at different temperatures due to differences in material composition.
Three, how does the engineer ensure the sealing of the low temperature valve?
Leakage is very expensive when one considers the cost of making the gas into a refrigerant in the first place. It’s also dangerous. A big concern with cryogenic technology is the possibility of seat leakage. Buyers often underestimate the radial and linear growth of stems in relation to the body. Buyers can avoid these problems if they choose the right valves. It is recommended to use a low temperature valve made of stainless steel. The material copes well with temperature gradients during operation with liquefied gases. Cryogenic valves shall be sealed with suitable materials up to 100 bar. In addition, the EXTENDED BONNET IS a very important feature as it determines the tightness of the stem sealant.

Select a valve for low temperature service
Selecting valves for cryogenic applications can be complex. The buyer must consider the conditions on the ship and in the factory. Furthermore, the specific properties of cryogenic fluids require specific valve performance. Proper selection ensures plant reliability, equipment protection and safe operation. The global LNG market uses two major valve designs.
1, single baffle and double baffle check valve
These valves are critical components in liquefaction equipment because they prevent damage caused by flow reversal. Material and size are important considerations because cryogenic valves are expensive. The results of incorrect valves can be harmful.
2, three bias rotary tight isolation valve
These offsets allow the valve to open and close. They operate with very little friction and friction. It also uses stem torque to make the valve more airtight. One of the challenges of LNG storage is being trapped in a cavity. In these cavities, the liquid can be expanded more than 600 times. The three-rotary tight isolation valve eliminates this challenge.
Five, in the case of highly flammable gas, such as natural gas or oxygen, in the event of a fire, the valve must also operate correctly.
1. Temperature problem
Drastic temperature changes can affect the safety of workers and factories. Each component of the cryovalve expands and contracts at different rates due to different material compositions and the length of time they are subjected to the refrigerant. Another big problem when dealing with refrigerants is the increase in heat from the surrounding environment. These heat increases are the reason manufacturers isolate valves and lines. In addition to the high temperature range, valves must contend with considerable challenges. For liquefied helium, the temperature of the liquefied gas drops to -270C.
2. Functional problems
Conversely, if the temperature drops to zero, valve function becomes very challenging. The cryogenic valve connects the pipe with liquid gas to the environment. It does so at ambient temperature. The result can be a temperature difference of up to 300C between the pipe and the environment.
3. Efficiency
Temperature differences generate heat flow from warm to cold zones. It can impair the normal function of the valve. It can also reduce the efficiency of the system in extreme cases. This is of particular concern if ice forms on the warm end. But in cryogenic applications, this passive heating process is also used deliberately. This process is used to seal the stem. Usually, the stem is sealed with plastic. These materials cannot withstand low temperatures, but a high-performance metal seal for two components, which move a lot in opposite directions, is just very expensive and almost impossible.
4. Stress
There is a build-up of pressure during the normal handling of the refrigerant. This is due to the increase in ambient heat and subsequent steam formation. Special care is required in the design of valve/piping systems. This allows stress to build up.
5. Sealing problem
There is a very simple solution to this problem. You take the plastic used to seal the stem to a relatively normal temperature area. This means that the stem sealant must be kept at a distance from the fluid. The hood is like a tube. If the fluid rises through this pipe, it will warm from the external temperature. When the fluid reaches the stem sealer, it is primarily at ambient temperature and gaseous. The hood also prevents the handle from freezing and failing to start.