Key Design Considerations of High-Temperature Control Valves

 
In automation control systems, high-temperature control valves play a crucial role, especially in extreme environments exceeding 450°C. These valves are essential for precisely regulating the flow of high-temperature fluids, facing significant challenges related to material expansion, deformation, and sealing performance under high temperatures. Therefore, the design and selection of high-temperature control valves are both complex and critical. This article will delve into the key technical aspects of high-temperature control valves, discussing material selection, design requirements, and analyzing common types of high-temperature control valves to better understand and address control needs in extreme conditions.

Material Selection for High-Temperature Control Valves

 
The performance of high-temperature control valves in extreme temperature environments directly depends on the choice of materials. To ensure the valve operates reliably under high temperatures, the materials must be carefully selected and rigorously tested for high-temperature resistance, corrosion resistance, and strength. Below are material selection strategies and their characteristics for different temperature ranges.

1. Environments Below 500°C

 
Material Selection: In environments below 500°C, control valve materials need to have high-temperature resistance and corrosion resistance. Common materials include high-temperature alloys such as nickel-based and cobalt-based alloys, which maintain good mechanical properties at elevated temperatures.

2. Environments Above 538°C

 
Chromium-Molybdenum Steel: For high-temperature environments of 538°C and above, chromium-molybdenum steel is a preferred material. Its high-temperature strength and corrosion resistance make it suitable for extreme conditions, effectively resisting oxidation and creep at high temperatures.

3. Environments Up to 1035°C

 
SUS310S Stainless Steel: For environments up to 1035°C, SUS310S stainless steel is commonly used. This stainless steel has a carbon content strictly controlled between 0.04% and 0.08%, ensuring stability and resistance to thermal deformation at extreme temperatures. It offers excellent high-temperature oxidation resistance and strength.

4. Environments Above 1200°C

 
Non-Metallic Heat-Resistant Materials: For even higher temperatures, non-metallic heat-resistant materials can be used. These materials, such as ceramics and silicon carbide, can withstand extreme temperatures up to 1200°C.
High-Temperature High-Strength Alloys: Examples include alloys used in engine combustion chambers, capable of direct use in environments around 1000°C, providing exceptional high-temperature performance. These alloys feature excellent thermal fatigue resistance and strength.

Design Requirements for High-Temperature Control Valves

 
In high-temperature environments, the design of control valves must meet a series of stringent requirements to ensure stability and performance under extreme conditions. These design requirements cover aspects such as packing selection, stem design, and sealing methods to address the challenges of high-temperature operation. The main design requirements for high-temperature control valves are as follows.

1. Packing Selection

 
PTFE (Polytetrafluoroethylene): PTFE packing is suitable for environments below 200°C. Its excellent chemical resistance and low friction coefficient make it perform well in lower temperature conditions. For medium to high-temperature applications, extended valve covers are needed to prevent packing from being affected by extremely high temperatures.
Flexible Graphite Packing: For high-temperature conditions, flexible graphite packing is recommended. This packing can withstand temperatures up to 600°C and offers excellent compressibility and sealing performance. It effectively reduces the height of extended valve covers, enhancing sealing effectiveness.

2. Stem Design

 
Rotary Valve with Heavy Stem: In high-temperature conditions, the strength and stability of the stem are crucial. A "rotary valve with a heavy stem" design can effectively improve the overall strength of the valve and reduce strength degradation and bending due to high temperatures. This design enhances the valve's high-temperature endurance and service life.

3. Sealing Methods

 
Environments Below 500°C: For environments below 500°C, special composite graphite seat soft seals can be used. This sealing method effectively addresses sealing needs in medium to high-temperature environments, ensuring reliable sealing within the normal operating temperature range.
Environments Above 500°C: In high-temperature environments above 500°C, control valves require metal-to-metal hard sealing. Common designs include butterfly valve structures, which provide reliable cut-off performance and maintain stability under extreme high temperatures.

Common Types of High-Temperature Control Valves

 
Several types of high-temperature control valves are commonly used, each suited for different high-temperature environments and offering specific performance characteristics.

1. Standard High-Temperature Alloy Butterfly Valve

 
Characteristics: Standard high-temperature alloy butterfly valves feature a simple structure, lightweight, and ease of forging. These valves are cost-effective, suitable for applications with less stringent leakage requirements.
Application: During use, ensure there is sufficient clearance between the valve body and disc to prevent jamming due to material thermal expansion. Proper positioning measures are needed to ensure effective disc positioning and avoid sagging or misalignment that could lead to jamming or seizing.

2. High-Temperature Alloy Damper Butterfly Valve

 
Characteristics: This type of high-temperature control valve is designed to address common sealing issues in high-temperature conditions. It has a simple structure, good sealing performance, and reduces the use of high-temperature alloys.
Sealing Method: Utilizes a flat damper (disc) seating on the valve body's boss to form a circular line sealing surface, offering excellent sealing performance for high-sealing applications.

3. High-Temperature Thermal Oil Ball Valve

 
Characteristics: This ball valve uses an elastic laminated special composite graphite seat and flexible graphite packing, specifically designed for thermal oil processes. It effectively addresses requirements for good cut-off, regulation, and resistance to thermal oil effects.
Advantages: Performs excellently in environments below 500°C, suitable for applications requiring high cut-off performance and sealing.

3. Ultra-High-Temperature Butterfly Valve with Non-Metallic Liner

 
Characteristics: This butterfly valve features ultra-high-temperature alloy materials for the valve body and non-metallic heat-resistant liners, ensuring strength and durability. The valve disc may be hollow or made of ultra-high-temperature alloys, with cooling or circulation methods to maintain performance in extreme high-temperature environments.
Application: Suitable for ultra-high-temperature environments around 1200°C, meeting fluid control needs under extreme conditions.

The selection and design of high-temperature control valves must comprehensively consider material performance, packing temperature resistance, and sealing methods to ensure stable operation and high efficiency in extreme high-temperature environments. These valves play a critical role in various industrial applications, such as chemical processing, power generation, and metallurgy, requiring tailored designs and choices to achieve optimal operational performance and safety.