Key Considerations in the Design of High-Temperature Valves

In the design of high-temperature valves, several factors must be carefully considered to ensure their reliability and durability under extreme conditions. High temperatures can affect the valve's performance due to issues such as thermal expansion, thermal cycling, mechanical properties, and the interaction between the materials and the medium. This article will explore key design considerations for high-temperature valves, focusing on thermal expansion, material selection, sealing design, bolt performance, valve body design, and temperature limits.

Thermal Expansion and Gap Design

Thermal expansion is one of the critical factors affecting valve design in high-temperature environments. Due to differences in the coefficients of thermal expansion of various materials, even when the valve seat and valve core are heated at nearly the same time, their expansion rates may differ. To prevent parts from seizing or being damaged due to thermal expansion differences, it is essential to increase the working gap between the valve components in the design. The size of the gap should be determined based on the material's thermal expansion coefficient, operating temperature, and stress levels. This helps reduce the risk of component jamming or wear, thereby extending the valve's service life.

Thermal Cycling and Fatigue Aging

Thermal cycling refers to the periodic thermal stress caused by continuous temperature changes during valve operation. This alternating high-temperature variation can loosen the connection between the valve seat and guide bush, accelerating the fatigue aging of the valve components. Therefore, special attention should be paid to these potential thermal fatigue issues in the design process, with appropriate measures taken. For example, using an elastic valve seat structure can effectively reduce the gap problems caused by thermal expansion and provide stable sealing performance under thermal cycling conditions.

Material Selection

Material selection is critical in high-temperature valve design, as the mechanical properties of materials change significantly with temperature. Properties such as strength, hardness, plasticity, modulus of elasticity, and Poisson's ratio are all affected by temperature. Common high-temperature materials include stainless steel, heat-resistant alloy steel, and carbon steel. These materials offer good high-temperature strength and corrosion resistance, making them suitable for high-temperature environments.
The valve body material should have good hardness, impact strength, wear resistance, and cavitation resistance. These properties ensure the valve operates effectively under harsh high-temperature conditions. To enhance wear resistance, materials such as stainless steel can be selected, and surface hardfacing treatments can be applied. This not only improves wear resistance but also reduces cavitation.

Valve Body Design and Pressure Resistance

The valve body design must account for the pressure that may occur during operation. The thickness of the body walls should be designed to ensure that the valve maintains sufficient strength under high temperature and pressure conditions, preventing structural failure. The design should provide adequate pressure resistance and minimize the impact of corrosion. Typically, the body should be designed with a structure that can withstand a fixed pressure rating to ensure stable long-term operation in high-temperature and high-pressure environments.

Sealing Design

Sealing design is crucial for high-temperature valves. As temperature increases, the performance of sealing materials may degrade. Therefore, special design measures are needed to maintain sealing performance. The forced Wood seal is a common sealing method used in high-temperature valves. It works by compressing the gasket through the tightening of flange bolts, forming an effective seal. This type of seal is widely used in the design of small-diameter medium-temperature valves. By incorporating floating valve covers, sealing rings, and other components in the design, it is possible to ensure that the valve maintains a seal under high-temperature media pressure, with the sealing effect improving as the pressure increases.

Bolt Performance and Design

In high-temperature environments, the performance of bolts is particularly critical. At high temperatures, bolts may experience performance changes and relaxation. Therefore, design measures must be taken to prevent bolts from seizing under high temperatures. First, materials suitable for high-temperature environments should be selected, and coarse threads should be used to reduce friction. Additionally, it is important to consider that steel bolts may experience stress relaxation at temperatures above 300°C, which can decrease the bolt's preload. Therefore, it is crucial to ensure that the remaining preload in the bolts is higher than the required value and to regularly check the stability of the connections to prevent leaks or failures caused by relaxation.

Temperature Limits and Material Usage

In high-temperature valve design, it is essential to ensure that the valve's operating temperature does not exceed the maximum allowable temperature of the material. According to the ASME B31.3 standard, the maximum allowable temperature for different materials is clearly defined. This limit must be strictly adhered to during the design process. However, in actual applications, factors such as the corrosiveness of the medium and stress levels should also be considered, as they may lower the actual operating temperature of the valve materials. Therefore, designers should select materials based on the actual operating conditions and provide a reasonable safety margin in the design.

Conclusion

Designing high-temperature valves is a complex and detailed task that requires careful consideration of various factors, including thermal expansion, material selection, sealing design, bolt performance, and temperature limits. With proper design, valves can maintain stability and long-term performance under high-temperature conditions. In practical applications, valve performance is not only influenced by the material itself but also by factors such as the corrosiveness of the medium, operating pressure, and temperature changes. Therefore, thorough analysis and calculations are essential during the design process to ensure that each aspect meets the requirements for high-temperature operation, ultimately ensuring efficient and safe valve performance.