I have put forward the following suggestions on the classification of operating temperature of valves, which have been published in magazine “Valve”. A brief introduction is as follows:
-254°C～-101°C, it is “ultra low temperature valve”
The main material suitable for “ultra-low temperature valve” (-254°C [liquid hydrogen]～-101°C [ethylene]) must be austenitic stainless steel, copper alloy or aluminum alloy with face-centered cubic lattice. Their low temperature mechanical properties after heat treatment, especially the low temperature impact toughness must meet the standard requirements. The following austenitic stainless steels are available for ultra low temperature valves. ASTM A351 CF8M、 CF3M、 CF8、 CF3；ASTM A182 F316 、 F316L、 F304 、 F304L；ASTM A433 316、 316L 、 304 、 304L; And the low temperature steel CF8D designed and formulated by Lanzhou High Pressure Valve Factory (factory standard of Lanzhou High Pressure Valve Factory: GFQ81-93). The body, bonnet, gate or disc of the ultra-low temperature valve must be cryogenically treated in liquid nitrogen (-196°C) before finishing.
-100°C～-30°C, it is “low temperature valve”
The main materials suitable for low-temperature valves (-100°C~-30°C) include low-temperature austenitic stainless steel and ferritic and martensitic steels for low-temperature pressure-bearing parts. Austenitic stainless steels for low temperature include ASTM A351 CF8M 、 CF3M、 CF8 、 CF3， ASTM A182 F316 、 F316L、 F304 、 F304L，ASTM A433 316、316L、304、304L and CF8D. The above austenitic stainless steels are also suitable for working temperature of -100°C~-30°C. Ferritic and martensitic steels for low-temperature pressure-bearing parts include ASTM A352 LCA (-32°C)； LCB 、LCC (-46°C)； LC1 (-59°C)；LC2、 LC2.1 (-73°C)； LC3 (-100°C). Although the material in the ASTM A352 standard has a lower primary price, its chemical composition during smelting must have reliable and very strict factory internal control standards. The heat treatment process is complicated, and it needs to be quenched and tempered many times. When the low temperature impact toughness does not meet the standard requirements, it is not allowed to use the material as low temperature steel.
-29°C～200°C, it is “normal temperature valve”
We call valves that work in the temperature range of -29°C to 200°C as “normal temperature valves”. The main reason is: this temperature area is basically the suitable temperature for the main materials of the valve; and it is the upper limit of the corrosion-resistant working temperature of corrosion-resistant stainless steel in acid medium, for example: CF8, CF3; the working temperature of 304, 304L in nitric acid medium is ≤200°C; CF8M, CF3M; the working temperature of 316, 316L in acetic acid medium is ≤200°C; 200°C is the maximum temperature value of PTFE as the sealing element of the valve (such as: sealing valve seat, sealing gasket, packing, etc.); 200°C is the maximum working temperature of silicone rubber (SI), fluorine rubber (EPM); there are also valves that work in “hydrogen” conditions, and the dissociation of hydrogen molecules into hydrogen atoms is negligible below 200°C, etc. .
＞200°C～325°C, it is “medium temperature valve”
We call valves that work in the temperature range of >200°C ~ 325°C as “medium temperature valves”. The main reason is: this temperature area is an unsuitable area for PTFE, that is, PTFE cannot be used as the sealing element of the valve, but it is a suitable area for para-polyphenylene (PPL). Using para-polyphenylene as a sealing element, it can be used for a working temperature of ≤325°C; this temperature area is also the upper limit of the maximum working temperature of valves made of cast iron and other materials.
＞325°C～425°C, it is “sub-high temperature valve”
We call valves that work in the temperature range of >325 °C ~ 425 °C as “sub-high temperature valves”. The main reason is: for valves working in this temperature area, the materials of sealing elements cannot use non-metallic polymers, but must be metals and alloys that are resistant to high temperature and wear, that is to say, the valve working in this temperature area is a “hard seal” in the full sense. This temperature area is also the upper limit of the maximum working temperature of carbon steel. In addition, we call the valve working in this temperature area “sub-high temperature valve”, because although this area is a high temperature area, when it is used for common media in this temperature area (such as water, steam, air, oil, etc.), the main material of the valve can meet the requirements of carbon steel, without the need to use heat-resistant alloy steel or heat-resistant stainless steel higher than carbon steel. Therefore, it can be said that this temperature area is not a high temperature area in the true sense. Therefore, it is more appropriate to call the valve in this working temperature area “sub-high temperature valve”.
＞425℃～550℃, it is “high temperature grade I valve”, referred to as PI grade
The working temperature of the valve is 425~550°C, which is designated as high temperature grade I (referred to as PI grade). The main material of the grade PI valve is “high temperature grade I medium carbon chromium nickel rare earth titanium high-quality heat-resistant steel” based on CF8 in the ASTM A351 standard. Because PI grade is a specific name, the concept of using high temperature stainless steel (P) is included here. Therefore, if the working medium is water or steam, although high-temperature steel WC6 (t≤540°C) or WC9 (t≤570°C) can also be used; although high-temperature steel C5 (ZG1Cr5Mo) can also be used in the case of sulfur-containing oil, but can’t call them grade PI here.
＞550℃～650℃, it is “high temperature grade II valve”, referred to as PII grade
The working temperature of the valve is 550~650°C, which is designated as high temperature grade II (referred to as PII grade). PII grade high temperature valve is mainly used in heavy oil catalytic cracking unit of oil refinery, it includes high temperature lined wear-resistant gate valve used in three-rotation nozzle and other parts. The main material of the PII grade valve is “high temperature grade II medium carbon chromium nickel rare earth titanium tantalum reinforced heat-resistant steel” based on CF8 in the ASTM A351 standard.
＞650℃～730℃, it is “high temperature grade III valve”, referred to as PIII grade
The working temperature of the valve is 650~730°C, which is designated as high temperature grade III (referred to as PIII grade). PIII grade high temperature valve is mainly used in large heavy oil catalytic cracking unit of oil refinery. The main material of the PIII grade high temperature valve is “high temperature grade III medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel” based on CF8M in ASTM A351 standard.
＞730℃～816℃, it is “high temperature grade IV valve”, referred to as PIV grade
The working temperature of the valve is 730~816°C, which is designated as high temperature grade IV (referred to as PIV grade). The upper limit of the working temperature of the PIV valve is 816°C, because the maximum temperature provided in the international authoritative standard ASME B16.34 pressure-temperature grade selected for valve design is 816°C. In addition, after the working temperature exceeds 816°C, the steel is close to entering the forging temperature region. At this time, the metal is in the plastic deformation range. The plasticity of the metal is good, and it is difficult to withstand high working pressure and impact force without deformation. The main material of the PIV valve is “high temperature grade IV medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel” based on CF8M in ASTM A351 standard ; CK-20 and F310 in ASTM A182 standard (Note: the content of C ≥0.050%) and heat-resistant stainless steel such as F310H.
＞816℃, it is “high temperature grade V valve”, referred to as PV grade
The working temperature of the valve is above 816°C, which is called high temperature grade V (referred to as PV grade). PV grade high-temperature valve (used as a shut-off valve, not a valve like a regulating butterfly valve) must adopt special design methods, such as: lined with thermal insulation lining or water or air cooling, etc., to ensure the normal operation of the valve. Therefore, the upper limit of the working temperature of the PV grade high-temperature valve is not specified, because the working temperature of the valve is not controlled by the material alone, but is solved by a special design method, and the basic principle of the design method is the same. According to the working medium and working pressure and the special design method adopted, the PV grade high temperature valve can choose reasonable materials that can meet the valve. In PV grade high temperature valves, usually the flue flapper valve or butterfly valve flapper or butterfly plate are often selected from HK-30 and HK-40 superalloys in ASTM A297 standard, which can resist oxidation below 1150°C, and resist corrosion in reducing gas, but cannot withstand shock and high pressure loads.
The working temperature of the valve is divided into the above 10 grades, such a clear classification provides a more scientific basis for the design and manufacture of the valve and the selection of materials.