How is the pressure of the valve system converted between the national standard and the American standard?

The PN, Class, and N.m we usually use are all methods of expressing pressure, but the difference is that the pressure they represent corresponds to different reference temperatures, PN European system refers to the pressure corresponding to 120°C, and CLass American standard refers to the pressure corresponding to 425.5°C.

Therefore, in the engineering exchange, it is not only possible to simply convert the pressure, such as CLass300# should be 2.1MPa simply by pressure conversion, but if the use temperature is taken into account, its corresponding pressure will increase, which is equivalent to 5.0MPa according to the temperature resistance pressure test of the material.
There are two types of valve systems:

The other is the "nominal pressure" system represented by Germany (including our country) based on the allowable working pressure at room temperature (100 degrees in our country and 120 degrees in Germany).

One is the "temperature and pressure system" represented by the allowable working pressure at a certain temperature represented by the United States. In the temperature and pressure system of the United States, except for 150LB with 260 degrees as the benchmark, all other levels are based on 454 degrees. At 260 degrees, the allowable stress of a 150-pound (150psi = 1MPa) No. 25 carbon steel valve is 1MPa, and the allowable stress at room temperature is much larger than 1MPa, which is about 2.0MPa.

Therefore, it is generally said that the nominal pressure level corresponding to American Standard 150LB is 2.0MPa, the nominal pressure level corresponding to 300LB is 5.0MPa, etc.

Therefore, the nominal pressure and temperature pressure level cannot be changed according to the pressure conversion formula. PN is a pressure-related code represented by numbers, which is a convenient round integer for reference, PN is an approximate number of MPa resistance to normal temperature, which is the nominal pressure usually used in domestic valves. The Control Valve for carbon steel valve body refers to the maximum working pressure allowed when applied below 200°C; For cast iron valve body, refers to the maximum working pressure allowed when applied below 120°C; Control Valves for stainless steel valve bodies refer to the maximum operating pressure allowed when applied below 250°C. When the operating temperature rises, the withstand pressure of the valve body decreases.

American standard valves express nominal pressure in pounds, which are the results of the calculation of the bonding temperature and pressure of a certain metal, according to the ANSI B16.34 standard. The main reason why pound level and nominal pressure do not correspond to each other is that the temperature reference between pound level and nominal pressure is different.

We usually use software to calculate, but we also need to know how to use tables to check the weight level. Japan mainly uses K values to indicate pressure levels. For the pressure of gases, in China, we generally use the mass unit "kg" (instead of "jin"), the unit of kg. Its corresponding unit of pressure is "kg/cm2", and one kilogram of pressure is one kilogram of force acting on a square centimeter.

Similarly, corresponding to foreign countries, for the pressure of gas, the commonly used unit of pressure is "psi", the unit is "1 pound/inch2", which is "pounds per square inch", and the full name in English is Pounds per square inch. But it is more commonly used to call its unit of mass directly, that is, the pound (LB.), which is actually called LB. It is the aforementioned pound force.

Replace all units with metric units to calculate: 1 psi = 1 pound/inch2≈0.068 bar, 1 bar≈ 14.5 psi≈ 0.1MPa, Europe and the United States and other countries are used to use psi as a unit. In Class 600 and Class 1500, there are two different values corresponding to the European standard and the American standard, 11MPa (corresponding to the 600 pound class) is the European system regulation, which is the regulation in "ISO 7005-1-1992 Steel Flanges"; 10MPa (corresponding to the 600-pound class) is a regulation of the American system, which is specified in ASME B16.5. Therefore, it cannot be absolutely said that the 600 pound class corresponds to 11MPa or 10MPa, and the regulations of different systems are different.

Since the nominal pressure and the temperature reference of the pressure class are different, there is no strict correspondence between the two.