The difference between low temperature ball valve and ordinary ball valve

The working medium of the low-temperature ball valve is mostly flammable, explosive, and highly permeable substances. The minimum operating temperature can reach -269 ° C, and the maximum use pressure is 10MPa. The working conditions are relatively harsh. Therefore, the design, manufacturing, and inspection of the low temperature valve are very different from the normal temperature valve.

 

Low-temperature valve refers to a valve that can be used under low-temperature conditions. Generally, valve valves with a working temperature below -40 ° C is called a low-temperature valve. Low -temperature ball valves are one of the indispensable equipment for industrial industries such as petrochemical, air separation, and natural gas. The quality of quality determines whether it can be safe, economical, and continuously produced. With the development of modern technology, the use of low -temperature valves is becoming wider and wider, and demand is increasing.

 

From the perspective of materials, for example, the low -temperature ball valves of Viton VITON VITON VITON's low -temperature ball valves include CF8, LCB, LF1, F304, etc., which can be applied to different temperatures and medias, and relevant standards are formulated. The appearance quality requirements also strictly do the chemical composition, thermal treatment, mechanical performance, physical performance, welding supplement, post -welding heat treatment, detection, inter -crystal corrosion test (Austrian steel), impact test (low temperature valve), etc. Technical requirements.

 

According to the manufacturing standards and requirements of the low -temperature ball valve of the United States VTON VTON, the low -temperature ball valve has different characteristics from ordinary ball valves:

 

1 General design requirements for low temperature valves

 

(1) The valve and its bodies should have the ability to work for a long time under the temperature of the low temperature medium and the surrounding environment (generally 10 years or 3500 ~ 5000 cycles);

 

(2) The ball valve should not become a significant heat source relative to the low temperature media. This is because the inflow of heat will reduce the thermal efficiency, and the heat inflows will be excessive.

 

(3) The operation performance of the low -temperature medium should not have the effect of the operation performance of the fascia and the sealing performance of the filler;

 

(4) The structure of a valve component of direct and low -temperature medium should meet the relevant explosion -proof and fire prevention requirements;

 

(5) The valve components that work at low temperature cannot be lubricated, so measures need to be taken to prevent the frictional parts from being scratched.

 

The above requirements shall run through the design process of the low temperature valve. In addition, it should be noted that the above requirements are unique to the low -temperature valve. During the design of the low -temperature valve design, the requirements of the relevant general valve should also be complied with at the same time.

 

2 The cooling performance of the low temperature valve

 

The cooling performance of the low -temperature valve refers to the ability to cool from room temperature to the working temperature. This performance can be measured by the energy consumed by the valve in the above process, that is, in the process of the above process, it is measured by the calories passed to the low -temperature media. Cooling performance indicators are of great significance for low -temperature valves for cyclical work. However, it is not enough to use Q2 to measure the cooling performance of the low -temperature valve valve. The following indicators can be used:

 

3.1 Material selection of valve body, valve cover, valve seat, opening and closing parts

 

When the temperature is higher than -100 ° C, you can use iron stainless steel. When the temperature is lower than -100 ° C, the austenitic stainless steel is used. The low-pressure and small-caliber valve can be used to use copper alloy or aluminum alloy.

 

3.2 Valve Material Selection

 

Made of Austenite stainless acid -resistant steel must be treated with appropriate heat treatment to improve the tensile strength. At the same time, it must be placed (0.04 ~ 0.06mm), or nitrogen seepage treatment to improve surface hardness.

 

3.3 Selection of fastener material materials

 

When the temperature is higher than -100 ° C, the bolt material uses alloy steel such as Ni and CR-MO, and it needs to be properly treated to prevent the threaded bite. When the temperature is low -100 ° C, the bolt material can use Austeen stainless steel. Narut materials are generally used with MO steel or Ni steel, and the thread surface is used to apply sulfurization key.

 

3.4 Ship Material Shake choice

 

When the use temperature is higher than -196 ° C, and the low temperature uses the maximum pressure of 3MPa, the asbestos rubber plate made from asbestos from long fibers can be used; when the use temperature is higher than -196 ° C, and the low temperature maximum use pressure is 5MPa, the stainless steel band asbestos can be used. Winding pads, stainless steel band polyettetosylin tattin tangled pads or stainless steel band expanded graphite wrapped pads.

 

Here we need to emphasize that all low -temperature material components must be deeply cold before finishing to reduce the contraction and deformation of low temperature valves under low temperature operating conditions.

 

4 Low -temperature valve structure design

 

The structure of the low -temperature valve is different from the general valve. During the structural design of the low -temperature valve, in addition to considering the general requirements of the valve structure, it is also necessary to focus on solving the following problems:

 

(1) After the low temperature valve is closed, the low -temperature medium remaining in the valve body is rapidly gasification due to the rise in temperature, causing abnormal pressure in the valve body; ) The impact of cold deformation of parts on the valve; (4) The explosion -proof requirements of low temperature medium on parts and components.

 

It should also be noticed that in addition to working at low -temperature media, it is also necessary to work at the surrounding environment temperature, that is, work at a temperature of about 20 ° C. When designing valve components, it is necessary this point.

 

According to the actual needs of the work site, the following base wood requirements are proposed on the structural design of the low -temperature valve:

 

(1) The valve body should be able to fully bear the expansion and contraction caused by temperature changes, and the structure of the valve seat part will not cause permanent deformation due to temperature changes;

 

(2) The structure of the long -necked valve cover that can protect the filler letter;

 

(3) Use the valve petals that can maintain reliable sealing no matter how the temperature changes.

 

(4) Adopt the upper sealing structure;

 

(5) Valve seats and valve petals covering the welding structure of diamond chromium tungsten stacked welding structure;

 

(6) Use the pressure -leaking hole to prevent abnormal pressure. The position of the pressure pellet is determined by the valve structure. It can be located on the valve body, or it can be located on the gate.

 

4.1 Design of low -temperature ball valve body

 

The valve body is the main compression part of the valve. It must have a certain strength to ensure the normal work of the valve. Under the condition of low temperature, the low temperature stress, expansion and contraction of additional stress of the valve body are very large. To keep the valve sealing the side of the valve, the valve body must have a certain rigidity. At the same time, to prevent the destruction of low temperature stress, to avoid sharp corners, grooves, etc. in the valve body as much as possible.

 

4.2 The design of the low -temperature valve long -necked valve cover

 

The low -temperature valve needs to adopt the long -necked valve cover structure, which is the day to reduce the heat in the device in the outside world; to ensure that the temperature of the filler box is above 0 ° C, so that the filler can work normally; prevent the part from the part of the filling letter to the place where the filling is too cold, so The valve stems and parts of the valve cover at the upper part of the filling letter are frost or freezing.

 

The design of the long -necked valve cover is mainly the design of the neck length L. L refers to the distance from the bottom to the surface of the sealing seat (see Figure 1). It is related to factors such as heat dissipation area. The calculations are cumbersome and are generally obtained by the experimental law. Usually, it can be determined by Table 2.

 

In industrial applications, the neck size can be appropriately extended according to the actual situation of the scene (such as thermal insulation, operation space, location, etc.).

 

4.3 Design of Pressure Components

 

The problem of abnormal pressure generally only exists in the low temperature gate valve. When the gate valve is closed, the low -temperature medium remaining in the cavity in the valve body absorbs a large amount of heat from the surrounding environment and quickly vaporizes, generating high pressure in the valve body. The harm of abnormal pressure is very harmful. It may press the gate tightly on the valve seat, causing the gate to die, preventing the valve from working properly. Essence Therefore, measures must be taken to avoid.

 

Common measures are designing pressure holes and setting by bypass systems. For small -diameter valves (DN ≤ 300mm), you can directly design a pressure hole at the high -voltage side (that is, the import end), and the bypass system needs to be increased for large caliber valves. The low -temperature valve that increases the pressure pores or bypass systems must indicate the flow of the medium.

 

4.4 The design of the sealing device

 

When the valve is fully opened, a device that prevents the working medium from leaking towards the filler letter is called the L sealed device.

 

The sealing device has two functions. First, the upper sealing device can reduce the damage to the filling of the working medium. Industrial valves are in a state of opening at most working hours. If there is no upper seal device, the media pressure will directly act on the filler. The filling is in a state of pressure for a long time and is easy to get aging. Second, when the filler is leaked, the full valve is opened so that the upper sealing device is in a working state, and the filler can be replaced with pressure. Therefore, there must be a sealing device for the gate valve and the cut -off valve.

 

The upper cover can be used on the valve cover to welded the hard alloy of chromium tungsten, and then the craftsmanship made of fine processing and grinding (for the valve cover of the Auspace stainless steel material, it can be directly processed on the valve cap on the cover cover) It can also be grinded on the specially closed seal.

 

In short, during the design of the low temperature valve, we must comprehensively consider the various effects of low temperature on the valve, and adopt a reasonable structure to avoid the adverse effects of low temperature on the normal work of the valve.

 

5 testing of low temperature valve

 

In addition to the normal temperature test, low -temperature valve must also do low -temperature tests.

 

N room temperature test mainly includes the hydraulic pressure test, water pressure, air pressure sealing test, upper seal test, and opening and torque test.

 

The main purpose of the low temperature test is to test the operating performance and sealing performance of the low temperature valve under low temperature. The operating performance requires that the valve is open and flexible, and the mobile parts and sealing sidelines must not be abrasion and killed. The sealing performance requires that the leakage of the dense cover of the valve is less than the allowable leakage.

 

In short, the low-temperature ball valve requires the stainless steel that is treated with low temperature and cold treatment as a valve material. It must be treated with a lengthent. It can be durable on the occasion of -196 ° C LNG, liquid nitrogen, liquid oxygen, and liquefied natural gas medium.