Pressure-temperature rating

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The pressure-temperature rating of a valve is the maximum allowable operating pressure, expressed in gauge pressure, at a specified temperature. As the temperature rises, the maximum allowable operating pressure decreases accordingly. Pressure-temperature rating data serve as the main basis for selecting flanges, valves, and pipe fittings appropriately under different operating temperatures and pressures; they are also fundamental parameters in engineering design and manufacturing. The pressure-temperature ratings for various materials are provided in Chapter 4; standards for the pressure-temperature ratings of valves, fittings, and flanges have been established for many of them. I. American Standards: Under American standards, the pressure-temperature ratings for steel valves are specified in accordance with ASME/ANSI B16.5a-1992 and ASME B16.34-1996 ； The pressure-temperature ratings for cast iron valves are specified in ANSI B16.1-1989~B16.4-1989 and ANSI B16.42-1985; the pressure-temperature ratings for bronze valves are specified in ASME/ANSI B16.15a-1992 and ASME B16.24-1991. 1) The American standard ASME/ANSI B16.5a-1992 specifies two flange size series, one in imperial units and the other in metric units, and it also lists the pressure and temperature ratings for flanges under each of these unit systems. The method for determining the pressure-temperature ratings in imperial units is given in Appendix D of this standard. 2) The American standard ANSI B16.42-1985 \"Flanges for ductile iron pipes and flanged pipe fittings\" specifies the pressure-temperature ratings for CL150 and CL300 ductile iron flanges. The method for determining these pressure-temperature grades is outlined in the standard’s appendices; its basic principles, scope of application, limitations, and procedures are essentially consistent with those specified in ASME/ANSI B16.5a-1992. 3) The American standard ASME B16.34-1966 incorporates the temperature-pressure rating data for flanged valves from ASME/ANSI B16.5a-1992. The pressure-temperature ratings for flanged valves in this standard follow the methodology established in ASME/ANSI B16.5a-1992. This standard provides a pressure-temperature rating table for standard-grade valves with flange connections and weld connections, as well as for special-grade valves with weld connections. There are over 100 types of valve materials listed in the standards, which are grouped into 27 categories. II. German Standard: Volume 2 of the German standard DIN 2401-1977, titled \"Pressure Classes for Piping, Allowable Operating Pressures for Steel and Cast Iron Piping Components,\" is a relatively comprehensive standard for pressure-temperature ratings. It lists the allowable operating pressures of seamless pipes, welded pipes, flanges, valves, pipe fittings, and bolts under different materials and temperature conditions. This standard includes 6 types of flange materials, 4 types of materials for cast-iron valves with flange connections, 5 types of cast steel, and 5 types of forged steel; all of these are base materials. The steels are all carbon steel and low-alloy steel; stainless steel is not included. The standard specifies that when other materials different from the original material are used, the allowable operating pressure is calculated based on the ratio of the strength characteristic value of the material being used to the strength value of the original material specified in the standard at 20°C. The pressure-temperature ratings for stainless steel materials are further specified in ISO/DIS70651 \"Steel Flanges\". III. Former Soviet Union standards: The former Soviet Union standard TOCT356-1980 \"Series of nominal pressures, test pressures, and operating pressures for valves and piping fittings\" fully complies with the CMEA standards. In the former Soviet standards, materials were grouped. In this standard, the maximum allowable operating pressure values below 200°C are all considered to be the operating pressure at room temperature, and are equal to the nominal pressure. IV. International Standards The international standard ISO/DIS 7005-1-1992 \"Plain Pipe Flanges\" combines the American standard ASME/ANSI B 16.5a-1992 with the flange standards for nominal pressure classes in German standards. Therefore, the pressure-temperature rating standards also adopt, respectively, the methods for establishing flange pressure-temperature rating standards as well as the corresponding data from the United States and Germany. The nominal pressure classes PN0.25, 0.6, 1.0, 1.6, 2.5, 4.0 MPa specified in ISO/DIS 7005-1-1992 belong to the German flange system ； PN2.5, 10, 15, 25, 42 MPa belong to the American flange system. The pressure-temperature rating standards for each system apply only to the flange standards of that respective system. V. China’s **standard** GB/T 9124-2000 (Appendix A), “Technical Requirements for Steel Pipe Flanges,” draws on the principles and methods used in determining pressure and temperature ratings specified in Germany’s DIN 2401-1977 and the United States’ ASME/ANSI B 16.5a-1992 standards. By utilizing the flange materials commonly used in China and referring to the international standard ISO/DIS 7005-1-1992, pressure-temperature ratings for flanges suitable for two nominal pressure ranges (PN0.25–4.0 MPa, PN2.0–42.0 MPa) were established. The standard specifies the maximum allowable operating pressure for 13 flange materials at 12 nominal pressure grades, at operating temperatures ranging from 20 to 530°C.