Valves are indispensable to fluid control activities and play a key role in the control of all fluids. With the development of modern science and technology, the demand for high-temperature valves in engineering projects is increasing. High-temperature valves are used in petrochemical, chemical, and power industries. Due to the long-term effect of high temperature on the physical properties and mechanical properties of metal materials, when designing and selecting high-temperature valves, it is necessary to focus on the influence of high temperature on related factors. In the following, Yijun Jun has organized relevant knowledge about high-temperature valves for everyone, hoping to help everyone.
Commonly used high temperature valve type
High-temperature valves include high-temperature gate valves, high-temperature stop valves, high-temperature check valves, high-temperature, high-temperature butterfly valves, high-temperature needle valves, high-temperature throttle valves, and high-temperature pressure relief valves. Among them, the more commonly used gate valve, globe valve, check valve, ball valve.
High-temperature valve design points
When designing high-temperature valves, special attention should be paid to the effects of thermal expansion, heat exchange, and mechanical properties of the material. Due to the difference in coefficient of thermal expansion of the material and the heat load carried by the part, even the valve seat and the valve core heated almost at the same time have different properties such as expansion at high temperatures; in order to effectively reduce the number of stuck or rubbed due to temperature between parts Injuries need to properly increase the working gap between valve parts. The increase of this gap should be determined based on the thermal expansion coefficient, stress, and actual operating temperature of the material. High temperature heat exchange will lead to the loosening of the connection between the valve seat and the guide sleeve, which will aggravate the fatigue aging of the valve parts. In the design, corresponding measures shall be taken according to the specific conditions, such as the elastic valve seat is preferred for the seal structure. High temperature will significantly affect the mechanical properties of the material. The strength, hardness, plasticity, elastic modulus, and Poisson's ratio of the material at different temperatures will also be different. The influence of these factors on the performance of the valve must be fully considered in the design.
Body material required
1. Material in the valve body
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 wear resistance and cavitation properties of the valve body, allowing them to work in high temperature environments.
In high-temperature environments, the presence of medium corrosion will have a great impact on the choice of materials. Because it is used in high-temperature environments, materials with better material properties should be selected, 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 normally in high temperature environment.
2. The design of the shell 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 housing pressure, so as to ensure sufficient pressure resistance, which can effectively minimize the corrosion degree.
3. The middle of the seal design
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 valve cover 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.
4 high temperature bolts to do the work of the connection
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, avoid screwed threads in the high temperature environment. Second, in addition to scientific and reasonable material selection, the thread should also be designed as a coarse thread and the radius of the gap should be increased within a suitable 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.
5. The coordination of gaps 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 may occur easily.
High temperature valve commonly used materials and its maximum use temperature
During the design of high temperature valves, it should be noted that the operating temperature must not exceed the maximum allowable operating temperature of the material. According to ASME B31.3 high temperature valve commonly used materials, see the figure below. In particular, it is necessary to consider factors such as medium corrosivity and stress level in the actual valve design. The permissible temperature of the valve material is actually lower than the value in the table.