How to choose the material for high-temperature valves from 550°C to 1100°C?

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Under high-temperature operating conditions, the maximum allowable operating temperature of the valve material is one of the key parameters determining the safe operation, stability, and service life of the equipment. Due to differences in composition ratios and microstructure, materials of different types exhibit significant variations in their temperature resistance limits. Chromomolybdenum steel, stainless steel, and nickel-based alloys are the three most commonly used materials for high-temperature valves in industrial applications. Their temperature resistance properties must be considered when selecting these valves, in order to avoid safety hazards such as seal failure and structural deformation caused by operation at temperatures above their limits. By adding chromium and molybdenum to carbon steel, chromomolybdenum steel significantly improves the material’s resistance to creep and oxidation, addressing the issues of graphitization and strength degradation that occur in ordinary carbon steel at high temperatures; it is therefore the preferred material for use in high and medium-temperature applications. Among the common grades, 15CrMoG (corresponding to ASTM A217 WC5 material) has a long-term temperature resistance limit of around 540–550°C, making it suitable for applications such as auxiliary steam in power plants ； The WC9 grade can withstand temperatures up to 593°C, and is commonly used in applications such as the main steam pipes of subcritical units in thermal power plants ； In conventional designs, the 2.25Cr-1Mo material can withstand temperatures of around 565–590°C; when used in applications that require stress reduction, it can tolerate temperatures up to 650°C. It is capable of withstanding high-temperature environments such as those found in hydrogenation units, and its temperature resistance is directly related to the synergistic strengthening effect of chromium and molybdenum elements. Among stainless steel materials, austenitic stainless steel is used in a wider range of applications due to its excellent corrosion resistance and high-temperature stability. The recommended maximum operating temperature for 304 stainless steel is 550°C over the long term (304H can be used if higher temperature resistance is required); it is suitable for controlling high-temperature fluids that do not cause severe corrosion ； 316L stainless steel can withstand temperatures of around 550–560°C over the long term, and is suitable for use in corrosive high-temperature media containing sulfur ； 321 stainless steel contains titanium, offering excellent resistance to intergranular corrosion; it can withstand temperatures up to 650°C over long periods of time, making it suitable for high-temperature, humid steam systems ； Due to its high chromium and nickel content, 310S stainless steel exhibits excellent oxidation and creep resistance, with a long-term temperature tolerance of up to 700°C in oxidizing atmospheres; it is commonly used in heat treatment furnaces, incinerator exhaust systems, and other applications involving high temperatures. Nickel-based alloys are the preferred choice for ultra-high temperature applications. Thanks to the excellent high-temperature stability of nickel, combined with the strengthening effects of elements such as chromium, molybdenum, and niobium, their temperature tolerance is significantly higher than that of chromomolybdenum steels and stainless steels. Inconel 625 can be used continuously at temperatures of around 650–700°C over the long term; short-term peak temperatures can reach 815°C. It is suitable for use in applications such as the outlets of petrochemical cracking furnaces and high-temperature gas systems ； Inconel 718 can withstand temperatures of 650–700°C over long periods of time, and up to 980°C for short periods (≤1 hour); it possesses both high-temperature strength and corrosion resistance ； High-end grades such as Haynes 282 can maintain performance at temperatures ranging from 650 to 950°C over extended periods; the directional solidification process further enhances their creep strength, making them suitable for use in extreme-high-temperature applications such as nuclear power and concentrated solar power generation. Furthermore, for nickel-based alloys such as Hastelloy C-276, the recommended long-term operating temperature range is 540–590°C; they resist strong acid corrosion and are suitable for use with acidic fluids at medium to high temperatures. It should be noted that the temperature tolerance limit of high-temperature valves is not the only criterion for selection; factors such as the corrosivity of the medium and the operating pressure must also be taken into account. Additionally, the temperature resistance of the sealing materials and seal surface materials needs to be considered – flexible graphite packing is recommended for long-term use in air at temperatures of 450–500°C, and it can withstand temperatures up to 1600°C in inert environments, making it the preferred choice for high-temperature sealing ； Cobalt-based alloys used for surfacing sealing surfaces (such as Stellite 6) can withstand temperatures of over 850°C, thereby enhancing their resistance to erosion and wear. In practical applications, it is necessary to select the shell material, sealing materials, and weld layers for the sealing surfaces based on the operating temperature, in order to create a comprehensive temperature-resistant system that ensures the long-term reliable operation of high-temperature valves.