An Introduction to Large Diameter Carbon Steel Flanges

There are some perforations bolts can go through on large diameter carbon steel flanges, and the bolts can make two flanges tightly connected with each other. Flanges are sealed through the gaskets. When the sizes of large diameter carbon steel flanges need to be determined, the nominal diameter as well as the nominal pressure of the flanges are supposed to be known. The nominal diameter of the pressure vessel flange should be two times the nominal diameter of the pressure vessel. For example, the pressure vessel with DN1000mm should be equipped with the large diameter flange with DN2000mm.

The nominal pressure of the large diameter flange is determined by the maximum operating pressure, the operating temperature and the material of the flange. The size and thickness of the flange are calculated and determined according to the  mechanical properties of the 20MnR flange at 250℃. Therefore, for the the flange with the size determined according to this benchmark, its maximum allowable operating pressure is considered to be its nominal pressure when it is at 200℃.

The deflection and warp of the flange caused by the joint action of the bolt and internal pressure make the stress distributed on the surface of the gasket uneven. The radial stress is obviously small inside and large outside, and with the increase of the flange’s diameter, the unevenness of the radial stress becomes more obvious. The circumferential stress distribution is relatively uniform because there are enough bolts. These results show that the insufficient stiffness problem is existing in the current standard of the flange. Among the A-type flange, the B-type flange and the large diameter flange, the A-type flange has relatively low stiffness, which makes it can only be used under the low pressure conditions; the B-type flange has high stiffness and the cylinder which will not be affected by the bending moment resulting from the deformation of the flange, which make it can be applied to the device with the large size; the large diameter flange has the highest stiffness and can bear the higher pressure. 

There are many processing methods for large diameter flanges. The processing methods should be customized for different customers, and different processing methods are supposed to be adopted for flanges made of various materials. The processing methods of large diameter flanges are totally different from those of the  small diameter flanges. The butt-joint connection or the splicing connection methods are usually used due to the large diameter. The processing methods for large diameter flanges are generally determined by the sizes of the flanges that customers choose.

Source: China Flanges Manufacturer – Yaang Pipe Industry (

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