The bolt flange connection consists of a pair of flanges, several bolts, nuts and a gasket. The flange is tightly pressed against the gasket by tightening bolts to achieve sealing. However, the performance of flange sealing depends on the following factors.

1. Bolt pre-tightening force

The pre-tightening force is an important factor affecting the seal. Appropriate pre-tightening force can ensure that the gasket can retain a certain seal specific pressure when working. If the pre-tightening force is too large, the gasket will be crushed or squeezed out, thereby breaking the ring seal. The distribution of the pre-tightening force on the gasket also affects the sealing performance. The way to ensure the uniform distribution of the pre-tightening force is to increase the number of bolts when the space required for tightening and disassembling the bolts is satisfied.

2. gasket sealing performance

Gasket is an important element to ensure sealing. The proper gasket material can make the gasket produce the necessary elastic deformation under the action of proper pre-tightening force without being crushed or squeezed out; the bolt is stretched under the action of internal pressure during work, making the flange The gap between the sealing surfaces is increased. At this time, the gasket material should have sufficient resilience to keep the gasket surface in close contact with the flange surface to continue to maintain good sealing performance; work should also be considered when selecting gasket materials Medium and working temperature. The width of the gasket is also an important factor affecting the seal. The wider the gasket, the greater the pre-tightening force required, and the larger the size of bolts and flanges is required. However, if the width of the gasket is too narrow, it may be crushed due to overload, causing the connection to fail.

3. Flange sealing surface characteristics

The form and surface characteristics of the flange sealing surface play a vital role in the influence of the sealing effect. Concave-convex surfaces and tongue-groove surfaces should be used for higher requirements. The flatness of the flange sealing surface and the perpendicularity between the sealing surface and the flange centerline directly affect the uniformity of the gasket force and the good contact between the gasket and the flange. The roughness of the flange sealing surface should match the requirements of the gasket. Radial knife marks or scratches on the surface are not allowed, let alone surface cracks.

4. flange stiffness and bolt stiffness

Insufficient rigidity will cause excessive warpage of the flange, resulting in seal failure. This is also the main reason for the failure of the flange seal. There are many factors that affect the rigidity of the flange, among which methods such as increasing the thickness of the flange and increasing the outer diameter of the flange can increase the rigidity of the flange and reduce the deformation. The bolt spacing is reduced, the bolt force is evenly transmitted to the gasket, and a uniform and sufficient sealing pressure is obtained, which can improve the sealing performance. Reducing the force arm acting on the bolt force can reduce the bending moment that the flange bears, which is conducive to sealing.

5. The influence of operating conditions

The operating temperature, pressure and the chemical and physical properties of the medium also affect the reliability of the flange connection. As the temperature increases, the viscosity of the medium decreases, and the increase in pressure increases the driving force of the medium to leak, and the tendency to leak increases; high temperature increases the chemical and physical activity of the medium, causing corrosion and dissolution of gaskets and flanges; It can cause creep and stress relaxation of bolts, flanges, and gaskets; gaseous media, such as hydrogen, have a small molecular weight and a greater possibility of leakage.