Petroleum, chemical flange standards have two categories, one is the pressure vessel flange standards, a class is the pipe flange standards.

 Flat welding and butt welding 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 liner ring, can save stainless steel.

When using flange standards to determine the flange size, shall know the nominal diameter of the flange and nominal pressure. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel to take the same series of values. For example, DN 1000mm pressure vessel, should be matched with DN 1000mm pressure vessel flange.

Nominal pressure of the flange is determined with the flange of the large operating pressure, operating temperature and flange materials. Because in the development of flange size series, the calculation of flange thickness, is to 16MnR at 200 ℃ mechanical properties as the benchmark. So the provisions of the flange size determined by this benchmark, at 200 ℃, its large allowable operating pressure is considered to have the size of the nominal pressure of the flange. For example, the so-called nominal pressure PNO.6MPa flange, is a flange with such a specific size, the flange is made of 16MnR, at 200 ℃, its large allowable operating pressure is 0.6MPa. if the PN0.6MPa flange used in conditions higher than 200 ℃, then its large operating pressure will be lower than its nominal pressure of 0.6MPa. Conversely, if it is used in conditions lower than 200°C, its high operating pressure is still determined by 200°C. If the material of the flange is changed to Q235-A, then the mechanical properties of Q235 an A steel are worse than 16MnR, and this flange with nominal pressure PN0.6MPa, even if it is operated 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, this flange with nominal pressure PN0.6MPa, when operating at 200℃, its big allowable operating pressure will be higher than its nominal pressure. 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 what is the large allowable operating pressure of this flange, it depends on the operating temperature of the flange and what material it is made of.