The PN and Class we usually use are a way of expressing pressure. The difference is that the pressure they represent corresponds to different reference temperatures. The PN European system refers to the pressure corresponding to 120 °C, while the CLass beauty The standard refers to the corresponding pressure at 425.5°C. Therefore, it is not possible to simply convert the pressure in the engineering interchange. For example, the pressure conversion of CLass300# should be 2.1MPa, but if the operating temperature is considered, the corresponding pressure will increase. According to the temperature and pressure resistance of the material The experimental determination is equivalent to 5.0 MPa. There are two types of valve systems: One is the 'nominal pressure' system represented by Germany (including my country) based on the allowable working pressure at room temperature (100 degrees in my country and 120 degrees in Germany). One is the 'temperature and pressure system' represented by the United States, which is represented by the allowable working pressure at a certain temperature. In the United States' temperature and pressure system, except for 150LB, which is based on 260 degrees, all other levels are based on 454 degrees. . The allowable stress of No. 25 carbon steel valve of 150 pounds (150psi=1MPa) is 1MPa at 260 degrees, and the allowable stress at normal temperature is much larger than 1MPa, about 2.0MPa. Therefore, generally speaking, the nominal pressure level corresponding to the American standard 150LB is 2.0MPa, and the nominal pressure level corresponding to 300LB is 5.0MPa and so on. Therefore, it is not possible to convert the nominal pressure and temperature and pressure grades according to the pressure conversion formula. PN is a pressure-related code expressed in numbers, and it is a convenient round integer for reference. PN is the number of pressure-resistant MPa that is approximately equivalent to normal temperature, and is the nominal pressure commonly used by domestic valves. For the control valve
with carbon steel body, it refers to the maximum allowable working pressure when applied below 200°C; for cast iron valve body, it refers to the maximum allowable working pressure when applied below 120°C; for the control valve with stainless steel body, it refers to the The maximum allowable working pressure for applications below 250°C. When the working temperature increases, the pressure resistance of the valve body will decrease. American standard valves express the nominal pressure in pounds, which is the calculation result of the combined temperature and pressure for a certain metal, which is calculated according to the standard of ANSI B16.34. The main reason why there is not a one-to-one correspondence between pounds and nominal pressures is that the temperature references of pounds and nominal pressures are different. We usually use software to calculate, but also know how to use tables to look up pounds. In Japan, the K value is mainly used to express the pressure level. For the pressure of gas, in China, we generally use its mass unit 'kg' to describe (instead of 'jin'), the unit is kg. The corresponding unit of pressure is 'kg/cm2', and one kilogram of pressure is one kilogram of force acting on one square centimeter. Similarly, corresponding to foreign countries, for the pressure of gas, the commonly used pressure unit is 'psi', the unit is '1 pound/inch2', which is 'pounds per square inch', the full English name is Pounds per square inch. But it is more commonly used to refer to its mass unit directly, that is, pounds (LB.), which is actually LB. It's the pound-force mentioned earlier. Converting all the units into metric units can be calculated: 1 psi=1 pound/inch2≈0.068bar, 1 bar≈14.5psi≈0.1MPa, Europe and the United States and other countries are accustomed to using psi as the unit. In Class600 and Class1500, there are two different values corresponding to the European standard and the American standard. 11MPa (corresponding to 600 pounds) is the European system regulation, which is stipulated in 'ISO 7005-1-1992 Steel Flanges'; 10MPa (corresponding to 600 pounds) Class) is the American system regulation, which is the regulation in ASME B16.5. Therefore, it cannot be absolutely said that 600 pounds corresponds to 11MPa or 10MPa, and the regulations of different systems are different. Since the nominal pressure and pressure rating have different temperature benchmarks, there is no strict correspondence between the two. The rough correspondence between the two is shown in the table below. Pound Rating and Nominal Pressure Comparison Table
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