The WN flange connection structure is an assembly, which is composed of a pair of flanges, several bolts, nuts and a gasket. In practical applications, the failure of the flange seal due to the strength damage of the coupling or the coupling is rare, and it is more common to leak due to poor sealing. Therefore, the main problem to be solved in the design of flange connection is to prevent medium leakage.

　　The principle of WN flange sealing is that the flange compresses the gasket between the sealing surfaces under the action of the bolt pre-tightening force. The pressure (compression stress) applied to the unit area must reach a certain value in order to deform the gasket and be compacted, and the micro-gap formed by machining on the sealing surface is filled to form the initial sealing condition. The required compression stress is called the gasket sealing specific pressure, expressed in y, in MPa.

　　The specific pressure of WN flange sealing is mainly determined by the gasket material. Obviously, when the material of the gasket is determined, the wider the gasket, the greater the pre-tightening force required for the gasket in order to ensure the proper specific pressure, so the size of the bolt and flange is also required to be larger, so the flange connection The middle gasket should not be too wide, and the entire flange surface should not be covered with gaskets.

　　When the WN flange equipment or pipeline is in working state, the axial force formed by the internal pressure of the medium causes the bolt to be stretched, and the flange sealing surfaces move in the direction of separation from each other, reducing the compression between the sealing surface and the gasket stress.