Comparison of the roughly corresponding relationship among the pressure grades of American standard, Japanese standard and national standard valves

Common pressure unit conversion formula of valve: 1bar=0.1MPa=1KG=14.5PSI=1kgf/m2

Nominal pressure (PN) and Class American standard pound (Lb) are both expressions of pressure. The difference is that the pressure they represent corresponds to different reference temperatures. PN European system refers to the corresponding pressure at 120 ℃, while Class American standard refers to the corresponding pressure at 425.5 ℃.

Therefore, in engineering interchange, pressure conversion cannot only be carried out. For example, the pressure conversion of CLAss300 # should be 2.1MPa, but if the use temperature is taken into account, the corresponding pressure will rise, which is equivalent to 5.0MPa according to the temperature and pressure test of the material.
There are two types of valve systems: one is the “nominal pressure” system represented by Germany (including China) and based on the allowable working pressure at normal temperature (100 ° C in China and 120 ° C in Germany). One is the “temperature pressure system” represented by the United States and the allowable working pressure at a certain temperature.
In the temperature and pressure system of the United States, except 150Lb, which is based on 260 ° C, other levels are based on 454 ° C. The allowable stress of No. 25 carbon steel valve of 150lb (150PSI=1MPa) at 260 ℃ is 1MPa, and the allowable stress at normal temperature is much greater than 1MPa, about 2.0MPa.
Therefore, generally speaking, the nominal pressure class corresponding to the American standard 150Lb is 2.0MPa, and the nominal pressure class corresponding to 300Lb is 5.0MPa, etc. Therefore, the nominal pressure and temperature-pressure grade cannot be changed according to the pressure transformation formula.
In addition, in Japanese standards, there is a “K” grade system, such as 10K, 20K, 30K, etc. The concept of this pressure grade system is the same as that of the British pressure grade system, but the measurement unit is the metric system.
Because the temperature reference of nominal pressure and pressure class are different, there is no strict correspondence between them. See Table for the approximate correspondence between the three.
Comparison table for conversion of pounds (Lb) and Japanese standard (K) and nominal pressure (reference)
Lb – K – nominal pressure (MPa)
150Lb——10K——2.0MPa
300Lb——20K——5.0MPa
400Lb——30K——6.8MPa
600Lb——45K——10.0MPa
900Lb——65K——15.0MPa
1500Lb——110K——25.0MPa
2500Lb——180K——42.0MPa
2500Lb——180K——42.0MPa
3500Lb——250K——56.0MPa
4500Lb——320K——76.0MPa

Table 1  Comparison table between CL and nominal pressure PN