The reference value related to the pressure resistance of piping system components refers to the design given pressure related to the mechanical strength of the piping component.
For users, PN and Class are both the identification methods of nominal pressure. The difference is that they represent different reference temperatures corresponding to the pressure, and they also represent the two commonly used "nominal pressure" systems for valves. Among them, PN is the commonly used pressure rating mark of the European standard system, which refers to the corresponding pressure at 120°C, while Class is the commonly used pressure rating mark of the American standard system, which generally refers to the corresponding pressure at 454°C.
01 Commonly used system of "nominal pressure"-PN vs Class
For the commonly used identification system for valve “nominal pressure”, the European Standard System (PN) is a “nominal pressure” system based on allowable working pressure at room temperature (120°C) represented by Germany. It is mostly used in ISO, DIN, EN, BS standards. The American Standard System (Class) is a "temperature-pressure" system represented by the allowable working pressure at a certain temperature, represented by the United States, and is mostly used in standards such as AMSE.
The Class series (namely pounds) in the American standard valve is a result of calculation based on ASME B16.34 after combining temperature and pressure for a certain metal. Because the temperature reference between the pound level and the nominal pressure is different, there is no one-to-one correspondence between the pound level and the nominal pressure, so the pressure conversion cannot be performed only in the engineering conversion. For example, Class300 should be 2.1MPa simply converted by pressure, but if the use temperature is taken into account, the corresponding pressure will increase accordingly. According to the temperature and pressure test of the material, it is equivalent to 5.0MPa. At the same time, in the US "temperature-pressure" system, other levels are based on 454°C, while Class150 is based on 260°C. The allowable stress of Class150 No. 25 carbon steel valve at 260℃ is 1MPa, and the allowable stress at room temperature is much larger than 1MPa, which is about 2.0MPa. Therefore, the nominal pressure and temperature and pressure levels cannot be changed casually according to the pressure conversion formula.
02 Commonly used "nominal pressure" system in China
At present, my country’s “nominal pressure” system mainly refers to the European standard. However, it is slightly different from that in Germany. The normal temperature reference used in Germany is 120℃, while in my country it is 100℃. my country’s national standard GB/T 1048-2019 The "Definition and Selection of Nominal Pressure of Piping Components" is drafted with reference to ISO 7268:1983 "Definition of Nominal Pressure of Piping Components". The degree of consistency between the national standard and the ISO standard is not equivalent.
The following table is taken from GB/T 1048-2019 "Definition and Selection of Nominal Pressure of Pipeline Components" (non-corresponding relationship)
03 Rough correspondence between the two
Since the nominal pressure and the temperature reference of the pressure grade are different, there is no strict correspondence between the two. The approximate correspondence between the two is shown in the table below.
The editor has something to say: Although the above table is roughly the same, PN20, PN50, PN110, PN150, PN260 and PN420 have been deleted in GB/T 1048-2019 "Definition and Selection of Nominal Pressure of Piping Components", using Class150, Class300, Class600, Class900 and Class1500 instead
This article is from the Internet and is for learning and communication purposes only