AOX丨What is the Difference Between the Nominal Pressure of National Standard and the American Standard?

Nominal pressure is an important parameter of the valve, usually expressed by the letters PN and nominal pressure value, representing the pressure to be withstood corresponding to different reference temperatures. The pressure system of the valve is commonly used in the national standard pressure system and the American standard pressure system, what are the differences between them and how to carry out a simple conversion, here is a detailed introduction to help valve users better understand.

PN national standard system refers to the pressure corresponding to 120 degrees Celsius, while CLass American standard refers to the pressure corresponding to 425.5 degrees Celsius (in addition to 150LB to 260 degrees as a benchmark, other levels are based on 454 degrees), 150 pounds of class (150psi = 1MPa) of 25 carbon steel valves at 260 degrees, the allowable stress is 1MPa, while the allowable stress at room temperature Therefore, it is generally said that the American Standard 150LB corresponds to a nominal pressure level of 2.0MPa, 300LB corresponds to a nominal pressure level of 5.0MPa, etc. So in the engineering interchange can not just pressure conversion, such as CLass300# pure pressure conversion should be 2.1MPa, but if you take into account the use of temperature, it corresponds to the pressure is increased, according to the material temperature pressure test measurement equivalent to 5.0MPa.

The nominal pressure is not the actual pressure value and cannot be casually converted according to the pressure conversion formula to change the nominal pressure and temperature pressure level.PN is a numerical code related to pressure, a convenient round integer to provide reference, PN is approximate to the number of pressure resistance MPa at room temperature, which is the nominal pressure usually used in domestic valves. For example, for carbon steel body of the gate valve, refers to the maximum working pressure allowed in the application below 200 ℃; for cast iron body, refers to the maximum working pressure allowed in the application below 120 ℃; for stainless steel body of the control valve, refers to the maximum working pressure allowed in the application below 250 ℃. When the operating temperature increases, the pressure resistance of the valve body decreases.

American Standard valves are expressed in pounds to nominal pressure, pounds is the result of the calculation of the combined temperature and pressure for a particular metal, which he calculated according to the standard ASME B16.34. The main reason why poundage and nominal pressure are not one-to-one is that the temperature reference for poundage and nominal pressure is different. We usually use software to calculate this, but it is also important to know how to use the tables to check the poundage. In Japan, pressure classes are mainly expressed in terms of K values. For gas pressure, in China we generally use the unit of mass "kilogram" (rather than "catty") to describe it in kg. The corresponding unit of pressure is "kg/cm2 "A kilogram of pressure is one kilogram of force acting on a square centimetre. Similarly, the common unit of pressure for gases abroad is "psi", in "1 pound/inch2", which is "pounds per square inch". "However, it is more commonly referred to directly as the unit of mass, the pound (LB.), which is actually the pound of force mentioned earlier. Converting all units into metric units can be calculated: 1 psi = 1 lb/inch2 ≈ 0.068 bar, 1 bar ≈ 14.5psi ≈ 0.1MPa, Europe and the United States and other countries are used to using psi as a unit. In Class600 and Class1500 there are two different values corresponding to the European and American standards. 11MPa (corresponding to 600 lb class) is the European system, which is stipulated in ISO 7005-1 Steel Flanges; 10MPa (corresponding to 600 lb class) is the American system, which is stipulated in ASME B16.5. Therefore, it is not possible to say absolutely that the 600 lb class corresponds to 11 MPa or 10 MPa, as the regulations vary from system to system.

It is worth noting that although the national standard pressure and the American standard pressure can be simply converted, there are many differences between them and the connection size is also completely different. In the actual use process, the valves used in the corresponding pressure system should be selected in accordance with the corresponding standards and should not be mixed.