Classification of valve operating temperatures

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1. From -254°C to -101°C: these are \"ultra-low temperature valves\". For such valves (from -254°C [liquid hydrogen] to -101°C [ethylene]), the material used for their construction must be austenitic stainless steel, copper alloys, or aluminum alloys with a face-centered cubic crystal structure. The low-temperature mechanical properties of these materials, 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 precision 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℃: These are \"low-temperature valves\". The main materials suitable for low-temperature valves operating in the range of -100℃ to -30℃ include low-temperature austenitic stainless steels, as well as ferritic and martensitic steels used for 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 conforming to the ASTM A352 standard, although their initial price is relatively low, their chemical composition during smelting must adhere to reliable and extremely stringent in-house factory 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 be used as low-temperature steel. 3. –29℃ to 200℃: These are known as “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 an unsuitable area for polytetrafluoroethylene; that is, polytetrafluoroethylene cannot be used as a sealing element for valves. However, it is a suitable area for para-phenylene polymer (PPL), and using para-phenylene polymer as a sealing element allows use at working 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°C to 425°C: “sub-high-temperature valves”. Valves that operate in this temperature range of >325°C to 425°C 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 a true \"hard seal\". 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 PⅠ class valves. Valves with an operating temperature of 425~550℃ are classified as High-temperature Class I (abbreviated as PI class). The main material of PI-class valves is \"high-temperature Class I medium-carbon chromium-nickel-rare-earth-titanium high-quality heat-resistant steel\" based on CF8 as specified in ASTM A351 standard. 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 referred to as PI grade in this case. 7. >550°C–650°C: These are “high-temperature Class II valves”, abbreviated as PII-class valves. The operating temperature range for these valves is 550–650°C; therefore, they are classified as high-temperature Class II valves (abbreviated as PII-class). 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℃, which classifies them as High-temperature Class III (abbreviated as PIII). Class PIII high-temperature valves are mainly used in large heavy oil catalytic cracking units in oil 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-reinforced heat-resistant steel\" based on CF8M as specified in ASTM A351 standards. 9. >730°C–816°C: This is classified as “High-Temperature Grade IV valves”, abbreviated as PIV valves. The operating temperature range for these valves is 730–816°C; therefore, they are categorized as High-Temperature Grade IV (abbreviated as PIV grade). 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 for pressure-temperature classifications, 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 such temperatures, 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 a working temperature of >816°C are classified as “High-temperature Class V valves”, abbreviated as PV valves; those with a working temperature above 816°C are referred to as High-temperature Class V valves (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 methods, and the basic principles behind these design methods 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 specific design methods employed. In PV-class high-temperature valves, the disc or butterfly element of flue gate valves or butterfly valves is usually made from the HK-30 or HK-40 superalloys specified in ASTM A297 standards; these materials can resist corrosion in oxidizing and reducing gases at temperatures below 1150°C, but they cannot withstand impact 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.