Valve material and working temperature
One of the major issues that must be considered when designing and selecting valves is the operating temperature of the valve. In order to regulate the suitable working temperature of the valve body material, the suitable working temperature and relevant conditions for the valve body materials used in the petrochemical, chemical, fertilizer, electric power and metallurgy industries in China are related to the material properties of various types of valve steels and alloys. Requirements have been made clear for the valve product design, manufacture and inspection. In addition, from the aspects of technology management, production management and material procurement, for each type of steel, a combination of good steel grades and alloy grades should not be used to prevent confusion.
2 Low temperature conditions
Ultra-low temperature valve (-254 (liquid hydrogen) -101 °C (ethylene)) The main material must use a faceted cubic lattice of austenitic stainless steel, copper alloy or aluminum alloy, its low temperature mechanical properties after heat treatment, especially low temperature impact Resilience must meet the requirements of the standard.
The following austenitic stainless steels can be used to make cryogenic valves. ASTM A351 CF8M, CF3M, CF8, and CF3, ASTM A182 F316, F316L, F304, and F304L, ASTM A433 316, 316L, 304, 304L, and CF8D (Lanzhou High Pressure Valve Plant Design, factory standard code GFQ81-93). The cryogenic valve body, bonnet, ram or flap must be cryogenically treated in liquid nitrogen (-196°C) before finishing.
3 Low temperature valve material
Suitable for cryogenic valves (-100 ~ -30 °C) of the main material of cryogenic austenitic stainless steel and cryogenic pressure parts with ferritic and martensitic steel.
Austenitic stainless steels for low temperature use include ASTM A351 CF8M, CF3M, CF8, and CF3, ASTM A182 F316, F316L, F304, and F304L, ASTM A433 316, 316L, 304, 304L, and CF8D.
Ferrite and martensitic steels for cryogenic pressure parts are ASTM A352 LCA (-32°C), LCB, LCC (-46°C), LC1 (-59°C), LC2, LC211 (-73°C) and LC3 ( -100°C).
The primary price of the material in the ASTM A352 standard is low, but the smelting chemical composition must have reliable and very strict factory internal control standards. The heat treatment process is complex and requires many times of conditioning to be able to meet the requirements of low temperature impact toughness required by the standard, with a long production cycle. When the low temperature impact toughness fails to meet the standard requirements, it is not allowed to use the material for cryogenic steel. Therefore, it is only used when the production volume is large and can be used for smelting, but austenite stainless steel is generally used.
4 Non-corrosive conditions
Carbon steel is generally used when the working medium of the valve is non-corrosive substances such as water, steam, air, and oil. Carbon steel for valves refers to WCB, WCC cast steel, and ASTM A105 forged steel in the ASTM A216 standard. The suitable working temperature for carbon steel for valves is -29 to 425°C. However, for the sake of safety, considering that the working temperature of the medium may fluctuate, the use temperature of carbon steel in general should not exceed 400°C.