Working principle of pressure vessel flange

The working principle of pressure vessel flange is that when the pre-tightening force is applied to the flange bolt, the bolt force compresses the gasket through the flange ring, forcing the flange gasket to produce compression deformation.(Sealing principle of pressure vessel flange)

When the bolt force reaches a certain value, the flange sealing surface and the four convex irregularities on the gasket are forced to be filled by the gasket deformation, which creates the initial sealing conditions for preventing the leakage of the fluid medium.

ANSI B16.47 ASTM A105 blind flanges

At this time, the pressure on the effective sealing area of the gasket unit is called the initial sealing specific pressure of the gasket. When the equipment or pipeline is subjected to medium pressure, the bolt is stretched by tensile stress, the flange sealing surface moves along the direction of separation, the compression force between the sealing surface and the gasket decreases, the gasket compression decreases, and the specific pressure of the pre-tight seal decreases. If the gasket has enough resilience, the deformation of gasket can compensate for the separation of bolt and sealing surface, and the specific pressure of pre-tightening seal can only be reduced to no less than the specific pressure of working seal, the flange will remain in good sealing condition.

On the contrary, if the springback ability of gaskets is insufficient, the specific pressure of seals drops below the specific pressure of working seals, and even the seals re-appear cracks, the seals will fail.