Flange Standard and Selection Method
There are two types of flanges for petroleum and chemical, one is pressure vessel flange, another one is pipe flange.
Both welded and welding neck flanges can be made with or without bush rings. When the equipment is made of stainless steel, we use carbon steel flange 7 and stainless steel ring, which can use less stainless steel.
We must know the nominal diameter and pressure of the flange to make sure the size of the flange on the basis of the flange standard. We often adopt the same numerical value of the nominal diameters for pressure vessel flange and pressure vessel. For example, pressure vessel with DN 1000mm should be equipped with pressure vessel flange with DN 1000mm.
The nominal pressure of the flange is determined by the maximum operating pressure of the flange, operating temperature and flange material. The formulation of flange sizes and calculation of flange thickness are based on a benchmark, that is, the mechanical properties of flange which is made by 16MnR under the temperature of 200℃. So the size of the flange determined by this benchmark, its maximum operating pressure is regarded as the nominal pressure under the temperature of 200℃.For example, the so-called flange
with nominal pressure PNO.6MPa is a kind of flange with the same size and made of 16MnR, its maximum operating pressure is 0.6MPa under the temperature of 200℃. If we use the PN0.6MPa flange under the temperature of 200℃, its maximum operating pressure will be lower than its nominal pressure (0.6MPa). On the contrary, if we use the flange below 200℃ with the same maximum working pressure and exchange the flange material for Q235-A, then the mechanical properties of Q235-A steel will be poorer than that of 16MnR. Even if we operate the flange with nominal pressure PNO.6MPa under the temperature of 200℃, its maximum operating pressure will be lower than its nominal pressure. And if we replace 16MnR with 15MnVR, maximum operating pressure of flange with nominal pressure PNO.6MPa will be higher than its nominal pressure under the temperature of 200℃, because the mechanical properties of 15MnVR is better than that of 16MnR. In short, as long as the nominal diameter of the flange, the nominal pressure are set, the size of the flange is determined. As for the maximum operating pressure of the flange, it depends on the operating temperature of flange materials.