The nominal diameter and pressure of the flange must be known when the flange size is determined by using the stainless steel flange standard. 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 vessel should be equipped with DN 1000mm pressure vessel flange. The determination of nominal pressure of flange is related to the maximum operating pressure, operating temperature and flange material. Because when making flange size series and calculating flange thickness, it is based on the mechanical properties of 16MnR at 200 C. Therefore, the maximum allowable operating pressure of the flange determined by this benchmark is considered to be the nominal pressure of the flange with this size at 200 C. For example, the so-called nominal pressure PNO.6MPa flange refers to the flange with such a specific size. The flange is made of 16MnR, and its maximum allowable operating pressure is 0.6MPa at 200C. If the PN0.6MPa flange is used at temperatures higher than 200 C, its maximum operating pressure will be lower than its nominal pressure of 0.6MPa.
On the contrary, if it is used under the condition of 200 C, the maximum working pressure is still determined according to 200 C. If the flange material is changed to Q235-A, the mechanical properties of Q235-A steel are worse than that of 16MnR. This flange with nominal pressure PN0.6MPa will have a maximum allowable operating pressure lower than its nominal pressure even if it is operated at 200 C. Conversely, if the material of flange is changed from 16MnR to 15MnVR, the maximum allowable operating pressure of the flange with nominal pressure PN0.6MPa will be higher than that with nominal pressure because the mechanical performance of 15MnVR is better than that of 16MnR. In short, as long as the nominal diameter and pressure of the flange are determined, the size of the flange is also determined.