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Abstract: Valves are indispensable for fluid control activities and play a key role in the control of all fluids. Modern science and technology is developing very rapidly. It has achieved great breakthroughs and development in different industries. Therefore, the demand for high-temperature valves has also become more and more, and the requirements for the design of high-temperature valves have also become higher and higher.
Keywords: high-temperature valve; structural material; performance 1 influence on the design of high-temperature valves. The effect of thermal expansion. The thermal expansion of the material and the difference between the heat load of the part and other conditions are the main factors that directly lead to the difference in thermal expansion. Therefore, in the process of high-temperature valve design, the influence of these factors should be fully taken into account. In order to make the temperature of the valve core conform to the temperature of the pipeline fluid as soon as possible, the valve stem with smaller cross-sectional area can be cooled by introducing hot high-temperature fluid into the valve with lower temperature. Because the cooling conditions of the valve seat are different from those of the valve core, the expansion amount is also different. Although the heating is performed at the same time, the final expansion amount and other properties are different. Therefore, in the determination of the working gap between the valve parts, it should increase the scope to ensure that in the case of high-temperature media, to avoid the phenomenon of stuck or scratches between parts, effectively reducing the parts due to temperature damage . However, the increase in the gap must also be moderate. It should be determined based on the coefficient of thermal expansion of the material, the stress, and the actual operating temperature.
The effects of heat change. The thermal alternating properties of the medium also have a certain influence on the interaction between the parts. For example, the connection between the valve seat and the guide bushing is likely to become loose due to changes in the medium's heat exchange and lose the original sealing effect. Therefore, when designing, the joints of the valve seat and the support should be seam welded or spot welded to ensure its sealing effect. In addition, large-diameter valves should use a body welded valve seat to prevent over-exposure to the parts of the valve that are in contact with the medium and are over-fatigued by the effects of alternating stress, and even lose their original function. In addition, during the design process, the selection of the elastic valve seat structure and the evaluation of its effects should be taken into account in the heat exchange condition. Only in this way can we fundamentally reduce the impact of heat exchange on the design of high-temperature valves, reduce the damage of parts and extend the life of high-temperature valves.
Bruising problem. If the interaction of the materials is small, due to external constraints and influences, it is very easy to have scratches. For example, in the piping system, the valve seat and the valve core often suffer from scratches, and their occurrence of scratches is mainly due to the entry of large particles. In addition, the impact of vibration may also have a great impact on the occurrence of scratches, so in order to reduce the scratch phenomenon in the use of activities, you need to make a reasonable choice of sealing materials, but also to ensure that the sealing room in the hardness of the matching control In the proper range.
The mechanical properties of the material. Under high temperature conditions, there are two major changes in the mechanical properties of the material that can occur: one is the change in the strength of the material, and the other is the change in the shape of the material itself. In addition, the hardness of the material fluctuates within a certain range as the temperature changes. However, the hardness of the material will have an effect on the performance of the valve sealing surface and the sealing performance of the valve, but also the service life of the valve. When the ambient temperature of the valve exceeds 450 degrees Celsius, it should be considered that in the event of a resilient elastic deformation of the valve parts in a high temperature environment, creep properties of the material will be deteriorated, and breakage will easily occur. If the temperature does not change, the speed of the creep with high stress will hit, and if the profit remains unchanged, the speed of creep with low temperature will also decrease. With the same material, the stress and temperature together determine the speed of creep.
2 The choice of high temperature valve material The choice of valve body material. The high temperature conditions and the corrosiveness of the medium will cause a certain influence on the choice of materials. Because the use environment is mostly in a high temperature environment, materials with good quality carbon steel, high-temperature alloy steel, and stainless steel should be selected as the valve body. The only way to ensure that the valve body can still be used normally under high temperature conditions.
Trim material selection. The coefficient of thermal expansion should be considered first and then combined with the scratch resistance of the moving parts under high temperature conditions, which in combination will enable the selection of trim materials. Most of the valve body material is 316 stainless steel, so as to improve the wear resistance of the valve body and improve the cavitation performance. The choice of valve trim material must be combined with the actual situation, select the materials that are suitable for use and meet the relevant requirements. If you want to ensure that the high-temperature valve on the structural material requirements, it should meet the following criteria: hardness, impact, and scratch resistance. While we make choices in the material inside the valve body, we should take the thermal expansion of the material as a key point. It should also consider the possibility of damage to components in high temperature environments. The material inside the valve body is made of stainless steel and can be surfacing on the surface. This can ensure the properties of the valve body such as wear resistance and cavitation, allowing them to work normally under high temperature conditions. In high temperature environments, the presence of media corrosion will have a great impact on the choice of materials, because it is used in high temperature environment, so you should choose materials with better material properties, such as carbon steel, high temperature alloy steel, Stainless steel and other materials as the valve body, this can ensure that the valve body can work in high temperature environment.
Shell design in terms of wall thickness. The design of the housing should consider the pressure that may occur during the specific use, and it should be designed as a fixed value of the withstand voltage of the housing so as to ensure sufficient pressure resistance and effectively minimize the corrosion. degree. The middle seal can be designed as a forced Wood seal. Its principle is to close the flange bolts tightly, so that the sealing gaskets use the compressive effect of pressure, and then a relatively small gap appears on the surface. In the design of medium-temperature small-diameter valves, such a forced seal is very common. Specifically, the forced Wood seal consists of the following components: valve body, floating valve cover, seal ring, etc. Before we perform the boost operation, we should fix the pinned bolts and move the floating lid upwards. The purpose of this is to keep the bonnet and the elastomeric pad well sealed. When the medium exerts pressure on it and can move upwards, the bolt can be effectively restrained. The sealing force of the bonnet and the elastic pad has a positive connection, and they can be strengthened with the increase of the pressure, and finally can produce a good sealing effect.
High temperature bolts do a good job of connecting. Because the bolts need to work in a high-temperature environment, several major issues should be considered: the bolts also have the connected properties changed, the forces relaxed, and so on. To solve the above problems, we can make the following design: First, to avoid screwed threads in high temperature environment. Second, in addition to the scientific and rational selection of materials, the thread should also be designed with coarse threads, and the clearance of the radius should be enhanced within an appropriate range. Third, when the steel bolt is at 300°C for a long period of time, a relatively loose force will occur. Therefore, it must be ensured that the remaining pre-tightening force is higher than the demand value, and the stability of the connection must be checked. The coordination of clearance should be scientific. A reasonable clearance should be ensured between the valve stem and the upper seal seat. The thermal expansion index of the material should ensure that the latter is greater than the former, otherwise, the problem of wear is likely to occur.
3 Hardened inner parts of high-temperature valves enhance surface hardness and wear resistance. High-temperature valve trims often experience an annealed or softened material because of excessive temperatures. This condition can easily cause galling of the trim surfaces. In order to reduce such damage, the hardness and impact strength of the valve trim in a high temperature environment should be improved, and the ability to deal with erosion and corrosion should be appropriately increased. Ceramics or alloys can be used on the surface of the valve body to increase the hardness and wear resistance of the valve body surface to ensure that the valve body can play its due role in the high temperature environment and extend its service life.
Surfacing layer thickness. In order to realize the hardening treatment of high-temperature valve inner parts, it is also necessary to confirm the thickness of the build-up welding layer. Through relevant experiments, it can be determined that the optimum thickness of the surfacing layer should be 4 mm or more. This thickness can better isolate the high temperature of the external environment, reduce the impact of external high temperature on the internal materials, and ensure the service life of the valve internal parts.
(Author: South Blower Co., Ltd.)
Keywords: high-temperature valve; structural material; performance 1 influence on the design of high-temperature valves. The effect of thermal expansion. The thermal expansion of the material and the difference between the heat load of the part and other conditions are the main factors that directly lead to the difference in thermal expansion. Therefore, in the process of high-temperature valve design, the influence of these factors should be fully taken into account. In order to make the temperature of the valve core conform to the temperature of the pipeline fluid as soon as possible, the valve stem with smaller cross-sectional area can be cooled by introducing hot high-temperature fluid into the valve with lower temperature. Because the cooling conditions of the valve seat are different from those of the valve core, the expansion amount is also different. Although the heating is performed at the same time, the final expansion amount and other properties are different. Therefore, in the determination of the working gap between the valve parts, it should increase the scope to ensure that in the case of high-temperature media, to avoid the phenomenon of stuck or scratches between parts, effectively reducing the parts due to temperature damage . However, the increase in the gap must also be moderate. It should be determined based on the coefficient of thermal expansion of the material, the stress, and the actual operating temperature.
The effects of heat change. The thermal alternating properties of the medium also have a certain influence on the interaction between the parts. For example, the connection between the valve seat and the guide bushing is likely to become loose due to changes in the medium's heat exchange and lose the original sealing effect. Therefore, when designing, the joints of the valve seat and the support should be seam welded or spot welded to ensure its sealing effect. In addition, large-diameter valves should use a body welded valve seat to prevent over-exposure to the parts of the valve that are in contact with the medium and are over-fatigued by the effects of alternating stress, and even lose their original function. In addition, during the design process, the selection of the elastic valve seat structure and the evaluation of its effects should be taken into account in the heat exchange condition. Only in this way can we fundamentally reduce the impact of heat exchange on the design of high-temperature valves, reduce the damage of parts and extend the life of high-temperature valves.
Bruising problem. If the interaction of the materials is small, due to external constraints and influences, it is very easy to have scratches. For example, in the piping system, the valve seat and the valve core often suffer from scratches, and their occurrence of scratches is mainly due to the entry of large particles. In addition, the impact of vibration may also have a great impact on the occurrence of scratches, so in order to reduce the scratch phenomenon in the use of activities, you need to make a reasonable choice of sealing materials, but also to ensure that the sealing room in the hardness of the matching control In the proper range.
The mechanical properties of the material. Under high temperature conditions, there are two major changes in the mechanical properties of the material that can occur: one is the change in the strength of the material, and the other is the change in the shape of the material itself. In addition, the hardness of the material fluctuates within a certain range as the temperature changes. However, the hardness of the material will have an effect on the performance of the valve sealing surface and the sealing performance of the valve, but also the service life of the valve. When the ambient temperature of the valve exceeds 450 degrees Celsius, it should be considered that in the event of a resilient elastic deformation of the valve parts in a high temperature environment, creep properties of the material will be deteriorated, and breakage will easily occur. If the temperature does not change, the speed of the creep with high stress will hit, and if the profit remains unchanged, the speed of creep with low temperature will also decrease. With the same material, the stress and temperature together determine the speed of creep.
2 The choice of high temperature valve material The choice of valve body material. The high temperature conditions and the corrosiveness of the medium will cause a certain influence on the choice of materials. Because the use environment is mostly in a high temperature environment, materials with good quality carbon steel, high-temperature alloy steel, and stainless steel should be selected as the valve body. The only way to ensure that the valve body can still be used normally under high temperature conditions.
Trim material selection. The coefficient of thermal expansion should be considered first and then combined with the scratch resistance of the moving parts under high temperature conditions, which in combination will enable the selection of trim materials. Most of the valve body material is 316 stainless steel, so as to improve the wear resistance of the valve body and improve the cavitation performance. The choice of valve trim material must be combined with the actual situation, select the materials that are suitable for use and meet the relevant requirements. If you want to ensure that the high-temperature valve on the structural material requirements, it should meet the following criteria: hardness, impact, and scratch resistance. While we make choices in the material inside the valve body, we should take the thermal expansion of the material as a key point. It should also consider the possibility of damage to components in high temperature environments. The material inside the valve body is made of stainless steel and can be surfacing on the surface. This can ensure the properties of the valve body such as wear resistance and cavitation, allowing them to work normally under high temperature conditions. In high temperature environments, the presence of media corrosion will have a great impact on the choice of materials, because it is used in high temperature environment, so you should choose materials with better material properties, such as carbon steel, high temperature alloy steel, Stainless steel and other materials as the valve body, this can ensure that the valve body can work in high temperature environment.
Shell design in terms of wall thickness. The design of the housing should consider the pressure that may occur during the specific use, and it should be designed as a fixed value of the withstand voltage of the housing so as to ensure sufficient pressure resistance and effectively minimize the corrosion. degree. The middle seal can be designed as a forced Wood seal. Its principle is to close the flange bolts tightly, so that the sealing gaskets use the compressive effect of pressure, and then a relatively small gap appears on the surface. In the design of medium-temperature small-diameter valves, such a forced seal is very common. Specifically, the forced Wood seal consists of the following components: valve body, floating valve cover, seal ring, etc. Before we perform the boost operation, we should fix the pinned bolts and move the floating lid upwards. The purpose of this is to keep the bonnet and the elastomeric pad well sealed. When the medium exerts pressure on it and can move upwards, the bolt can be effectively restrained. The sealing force of the bonnet and the elastic pad has a positive connection, and they can be strengthened with the increase of the pressure, and finally can produce a good sealing effect.
High temperature bolts do a good job of connecting. Because the bolts need to work in a high-temperature environment, several major issues should be considered: the bolts also have the connected properties changed, the forces relaxed, and so on. To solve the above problems, we can make the following design: First, to avoid screwed threads in high temperature environment. Second, in addition to the scientific and rational selection of materials, the thread should also be designed with coarse threads, and the clearance of the radius should be enhanced within an appropriate range. Third, when the steel bolt is at 300°C for a long period of time, a relatively loose force will occur. Therefore, it must be ensured that the remaining pre-tightening force is higher than the demand value, and the stability of the connection must be checked. The coordination of clearance should be scientific. A reasonable clearance should be ensured between the valve stem and the upper seal seat. The thermal expansion index of the material should ensure that the latter is greater than the former, otherwise, the problem of wear is likely to occur.
3 Hardened inner parts of high-temperature valves enhance surface hardness and wear resistance. High-temperature valve trims often experience an annealed or softened material because of excessive temperatures. This condition can easily cause galling of the trim surfaces. In order to reduce such damage, the hardness and impact strength of the valve trim in a high temperature environment should be improved, and the ability to deal with erosion and corrosion should be appropriately increased. Ceramics or alloys can be used on the surface of the valve body to increase the hardness and wear resistance of the valve body surface to ensure that the valve body can play its due role in the high temperature environment and extend its service life.
Surfacing layer thickness. In order to realize the hardening treatment of high-temperature valve inner parts, it is also necessary to confirm the thickness of the build-up welding layer. Through relevant experiments, it can be determined that the optimum thickness of the surfacing layer should be 4 mm or more. This thickness can better isolate the high temperature of the external environment, reduce the impact of external high temperature on the internal materials, and ensure the service life of the valve internal parts.
(Author: South Blower Co., Ltd.)
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