High-temperature control valves typically refer to control valves with operating temperatures exceeding 450°C. The core challenges in materials and manufacturing are severe thermal expansion and contraction leading to component jamming, and material creep at high temperatures causing a decline in mechanical properties.
The selection of valve body materials must be determined based on the temperature rating: for environments above 450°C, durable materials must be selected. For the 450~600°C (or 538°C) range, chromium-molybdenum steel, such as ASTM A217 WC9, is typically used. For the 600~1000°C (or up to 1035°C), stainless steel, such as SUS310S, is typically used, with the carbon content controlled between 0.04% and 0.08%. For temperatures above 1000°C (or 750°C), it is recommended to use non-metallic heat-resistant materials for lining (suitable for high-temperature applications up to 1200°C) or special high-temperature, high-strength alloys (such as the nickel-based alloy Inconel 625).
The materials of valve internals (valve core and seat) are usually the same as those of the valve body. To improve wear resistance at high temperatures, the sealing surfaces are often overlaid with hard alloys (such as the cobalt-based alloy Stellite 6).
The selection of sealing materials includes packing seals and seat seals. Standard polytetrafluoroethylene (PTFE) packing is only suitable for applications below 200°C; for medium and high temperature applications, flexible graphite packing with excellent temperature resistance up to 600°C or higher is required. For seat seals below 500°C, soft seals such as special composite graphite can be used; above 500°C, metal-to-metal hard seals are required.
Key manufacturing processes are special processes that ensure reliability at high temperatures. When the temperature reaches 750°C, a sealing weld process can be used on the valve seat to prevent leakage and erosion at threaded connections. Hard alloys (such as Stellite 6) are overlaid on the sealing surfaces of the valve core and seat to improve high-temperature wear resistance. Other processes include multi-stage pressure-reducing valve core processing, and heat dissipation design for valve bodies and actuators adapted to high temperatures (such as heat sinks and water-cooling jackets).