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1. From -254°C to -101°C: these are \"ultra-low temperature valves\". For such valves (operating in the range of -254°C [liquid hydrogen] to -101°C [ethylene]), the main materials must be austenitic stainless steels, copper alloys, or aluminum alloys with a face-centered cubic crystal structure. The low-temperature mechanical properties of these materials after heat treatment, especially their low-temperature impact toughness, must meet the specified standards. The following austenitic stainless steels can be used for ultra-low temperature valves. ASTM A351 CF8M, CF3M, CF8, CF3 ； ASTM A182 F316, F316L, F304, F304L ； ASTM A433: 316, 316L, 304, 304L; as well as the low-temperature steel CF8D designed and specified by Lanzhou High-Pressure Valve Factory (Lanzhou High-Pressure Valve Factory’s factory standard: GFQ81-93). Before final machining, the valve body, valve cover, gate, or disc of ultra-low temperature valves must undergo cryogenic treatment in liquid nitrogen (-196°C). 2. -100℃ to -30℃: This is the range for “low-temperature valves”. The main materials suitable for such valves are low-temperature austenitic stainless steels, as well as ferritic and martensitic steels used in low-temperature pressure-bearing components. Austenitic stainless steels for low temperatures include ASTM A351 CF8M, CF3M, CF8, CF3; ASTM A182 F316, F316L, F304, F304L; and ASTM A433 316, 316L, 304, 304L, and CF8D. The above austenitic stainless steels are also suitable for operating temperatures ranging from -100°C to -30°C. Ferritic and martensitic steels for low-temperature pressure parts have ASTM A352 LCA (-32°C) ； LCB, LCC (-46°C) ； LC1 (-59°C) ； LC2, LC2.1 (-73°C) ； LC3 (-100°C). For materials specified in the ASTM A352 standard, although their initial cost is low, the chemical composition during manufacturing must adhere to reliable and strictly enforced in-house control standards. Its heat treatment process is complex, requiring multiple quenching and tempering cycles. When the low-temperature impact toughness does not meet the standard requirements, it is not allowed to use it as low-temperature steel. 3. –29℃ to 200℃: These are \"normal-temperature valves\". Valves that operate within the temperature range of –29℃ to 200℃ are referred to as \"normal-temperature valves\". The main reason is that this temperature range is the one in which the materials primarily used for manufacturing valves are generally suitable ； Moreover, it represents the upper limit of the corrosion-resistant operating temperature for corrosion-resistant stainless steels in acidic media; for example: CF8, CF3 ； 304, 304L: operating temperature in nitric acid media ≤ 200℃ ； CF8M，CF3M ； 316, 316L: operating temperature in acetic acid media ≤ 200℃ ； 200°C is the maximum temperature at which polytetrafluoroethylene can be used as a sealing element for valves (such as sealing valve seats, gaskets, packing, etc.) ； 200°C is the maximum operating temperature for silicone rubber (SI) and fluororubber (EPM) ； There are also valves that operate under \"hydrogen-rich\" conditions, where the amount of hydrogen molecules dissociating into hydrogen atoms at temperatures below 200°C is negligible, and so on. 4. >200℃～325℃: These are “medium-temperature valves”. Valves that operate in the temperature range of >200℃～325℃ are referred to as “medium-temperature valves”. The main reason is that this temperature range is unsuitable for polytetrafluoroethylene; in other words, polytetrafluoroethylene cannot be used as a sealing element for valves. However, it is a suitable range for para-phenylene polymer (PPL), and using para-phenylene polymer as a sealing element allows use at operating temperatures up to 325℃ ； This temperature range is also the maximum operating temperature limit for valves made of materials such as cast iron. 5. >325℃～425℃: These are \"sub-high temperature valves\". Valves that operate in the temperature range of >325℃～425℃ are referred to as \"sub-high temperature valves\". The main reason is that for valves operating in this temperature range, the materials of their sealing elements cannot be non-metallic polymers; they must be metals and alloys that are resistant to high temperatures and wear. In other words, valves operating in this temperature range feature true \"hard sealing\". This temperature range is also the upper limit for the maximum operating temperature of carbon steel. Furthermore, we refer to valves that operate in this temperature range as \"sub-high temperature valves\" because, although it is a high-temperature range, when using the common media found in this range (such as water, steam, air, oils, etc.), carbon steel can be used as the material for the valve body, eliminating the need for more advanced heat-resistant alloy steels or heat-resistant stainless steels. Therefore, this temperature range can be said to not be a true high-temperature range; hence, it is more appropriate to refer to valves operating in this temperature range as \"sub-high-temperature valves\". 6. >425℃～550℃: These are \"High-temperature Class I valves\", abbreviated as P Class I valves. Their operating temperature ranges from 425 to 550℃, and they are classified as High-temperature Class I (abbreviated as PI class). The main material of PI-class valves is a high-temperature Class I medium-carbon chromium-nickel-rare-earth-titanium high-quality heat-resistant steel based on CF8 as specified in ASTM A351. Since the PI grade is a specific term, it encompasses the concept of high-temperature stainless steel (P) here. Therefore, when the working medium is water or steam, high-temperature steels WC6 (t≤540℃) or WC9 (t≤570℃) can also be used ； Although high-temperature steel C5 (ZG1Cr5Mo) can also be used with sulfur-containing oils, they cannot be classified as PI grade in this case. 7. >550℃～650℃: These are \"High-Temperature Class II valves\", abbreviated as PⅡ valves. Their operating temperature ranges from 550 to 650℃, and they are classified as High-Temperature Class II (abbreviated as PII). PII-class high-temperature valves are primarily used in the heavy oil catalytic cracking units of refineries; they include wear-resistant gate valves with high-temperature linings that are employed in components such as three-spin nozzles. The main material of PII-class valves is a \"high-temperature Class II medium-carbon chromium-nickel-rare-earth-titanium-tantalum strengthened heat-resistant steel\" based on CF8 as specified in ASTM A351 standards. 8. >650℃～730℃: These are \"High-temperature Class III valves\", abbreviated as P III valves. Their operating temperature ranges from 650 to 730℃, and they are classified as High-temperature Class III (abbreviated as PIII). Class PIII high-temperature valves are mainly used in large heavy oil catalytic cracking units in refineries. The main material for PIII-class high-temperature valves is a \"high-temperature Class III medium-carbon chromium-nickel-molybdenum rare-earth titanium tantalum strengthened heat-resistant steel\" based on CF8M as specified in ASTM A351 standards. 9. >730℃～816℃: These are \"High-Temperature Class IV valves\", abbreviated as PIV valves. Their operating temperature ranges from 730 to 816℃, and they are classified as High-Temperature Class IV (abbreviated as PIV class). The upper limit for the operating temperature of PIV-class valves is set at 816°C because the highest temperature specified in the internationally recognized standard ASME B16.34 pressure-temperature classification, which is used in the design of these valves, is 816°C. Moreover, when the operating temperature exceeds 816°C, the steel enters a region close to its forging temperature; at this point, the metal is in a state of plastic deformation, and its ductility is high, making it difficult for it to withstand high operating pressures and impacts without deforming. The main material of PIV-class valves is CF8M as specified in ASTM A351, which is a high-temperature Class IV medium-carbon chromium-nickel-molybdenum-rare-earth-titanium-tantalum strengthened heat-resistant steel” ； Heat-resistant stainless steels such as CK-20 and those specified in ASTM A182 standards, including F310 (note: with a carbon content of ≥0.050%) and F310H. 10. Valves with an operating temperature of >816°C are classified as “High-Temperature Class V valves”; abbreviated as PV valves. These valves operate at temperatures above 816°C and are thus referred to as High-Temperature Class V (abbreviated as PV class). PV-class high-temperature valves (used as shut-off valves, rather than control-type butterfly valves) must employ special design measures, such as thermal insulation linings or cooling with water or gas, in order to ensure their proper operation. Therefore, no upper limit is specified for the operating temperature of PV-class high-temperature valves, as controlling the operating temperature of these valves relies not solely on the materials used, but rather on special design techniques, and the basic principles behind these design techniques remain the same. For PV-class high-temperature valves, appropriate materials that can meet the requirements of such valves can be selected based on their operating medium, operating pressure, and the special design methods employed. In PV-class high-temperature valves, the vanes of flue gate valves or butterfly valves are usually made from the HK-30 or HK-40 superalloys specified in ASTM A297 standard; these materials can resist corrosion in oxidizing and reducing gases at temperatures below 1150°C, but they cannot withstand impacts or high-pressure loads. The operating temperatures of valves are divided into the 10 categories mentioned above; such a clear classification provides a more scientific basis for the design and manufacture of valves as well as for the selection of materials.