There are two types of flange standards used in petroleum and chemical industry, one is the pressure vessel flange standard, and the other is the pipe flange standard.

Both flat and butt-welded flanges are available with and without lining rings. When the equipment is made of stainless steel, the use of carbon steel flange 7 plus stainless steel lining ring, can save stainless steel.

When using the flange standard to determine the flange size, the nominal diameter and nominal pressure of the flange must be known. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel take the same series of values. For example, DN 1000mm pressure vessels should be equipped with DN 1000mm pressure vessel flanges.

The determination of the nominal pressure of the flange is related to the large operating pressure of the flange, the operating temperature and the flange material. Because in the development of flange size series, the calculation of flange thickness, is based on the mechanical properties of 16MnR at 200 ℃. Therefore, it is stipulated that when the flange size determined by this reference is 200 ℃, its large allowable operating pressure is considered to be the nominal pressure of the flange with this size. For example, a flange having a nominal pressure of PNO.6 MPa means a flange having such a specific size that the flange is made of 16MnR and has a large allowable operating pressure of 0.6MPa at 200°C. If the PN0.6MPa flange is used above 200 ℃, its large operating pressure will be lower than its nominal pressure of 0.6MPa. Conversely, if it is used under conditions below 200°C, its high working pressure is still determined at 200°C. If the material of the flange is changed to Q235-A, the mechanical properties of Q235-A steel are worse than 16MnR. The flange with nominal pressure PN0.6MPa, even if it operates at 200 ℃, its large allowable operating pressure will be lower than its nominal pressure.

On the contrary, if the material of the flange is changed from 16MnR to 15MnVR, then, because the mechanical properties of 15MnVR are better than 16MnR, the flange with nominal pressure PN0.6MPa will have a large allowable operating pressure higher than its nominal pressure when operating at 200 ℃. In short, as long as the nominal diameter and nominal pressure of the flange are determined, the size of the flange is also determined. As for the allowable operating pressure of this flange, it depends on the operating temperature of the flange and what material it is made.