The Main Factors Affecting The Sealing Performance

The main factors affecting the sealing performance of flange

A Bolt flange connection consists of a pair of flanges, a number of bolts, nuts, and a gasket. The flange is sealed by tightening the bolt and pressing the gasket. However, the sealing performance of the flange depends on the following factors.

Bolt preload

An important factor affecting sealing. The preload must compress the gasket to achieve an initial seal. Increasing the bolt preload can increase the sealing ability of the gasket because increasing the preload can make the gasket retain a larger specific pressure of the contact surface under normal conditions. But the preloading force should not be too large, otherwise, it will make the gasket yield overall and lose resilience, and even squeeze out or crush the gasket. In addition, the preload should be applied to the gasket as evenly as possible. The sealing performance is usually improved by reducing bolt diameter, increasing bolt number, and adopting the proper tightening method.

Gasket sealing performance

A gasket is an important component to ensure sealing. Suitable gasket material can make the gasket under the action of appropriate preloading force can produce the necessary elastic deformation, but not be crushed or extrusion; When working, the bolt is elongated under the action of internal pressure, so that the gap between the sealing surface of the flange is increased. At this time, the gasket material should have enough spring back ability to keep the gasket surface in close contact with the flange surface, so as to continue to maintain good sealing performance; When choosing gasket material, the working medium and working temperature should also be considered. The width of the gasket is also an important factor affecting the sealing, the wider the gasket, the greater the required preload, so that the size of the bolt and flange is also larger. However, if the gasket width is too narrow, it may be crushed due to overload, resulting in connection failure.

Flange-sealing surface features

The form and surface characteristics of the flange sealing surface play a crucial role in the sealing effect. Concave and convex surfaces and tenon surfaces should be used on higher occasions. The flatness of the flange sealing surface and the verticality between the sealing surface and the flange center line directly affect the forced uniformity of the gasket and good contact between the gasket and flange. The roughness of the sealing surface of the flange should be matched with the requirements of the gasket. The surface is not allowed to have radial knife marks or scratches but is not allowed to have surface cracks.

Flange stiffness and bolt stiffness

Insufficient stiffness will cause excessive warping deformation of the flange, leading to seal failure. This is also the main cause of flange seal failure. There are many factors affecting the flange stiffness, among which increases the thickness of the flange, increases the diameter of the flange, and other methods can improve the flange stiffness and reduce the deformation. Reducing the bolt spacing, so that the bolt force is evenly transferred to the gasket, uniform, and enough specific sealing pressure, can improve the sealing. The moment arm of decreasing bolt force can reduce the bending moment of the flange, which is conducive to sealing.

The influence of operating conditions

The influence of pressure, temperature, and physical and chemical properties of the medium on the sealing performance is very complex. The influence of simple pressure and medium on the sealing performance is not significant, but under the joint action of temperature, especially under the fluctuating high temperature, it will seriously affect the sealing performance and even make the seal completely fail due to fatigue. Because at high temperatures, the viscosity of the medium is small, permeability is large, easy to leak; The corrosion effect of the medium on the gasket and flange is intensified, increasing the possibility of leakage; Flange, bolt, and gasket will produce large high-temperature creep and stress relaxation so that the seal failure; Some non-metallic gaskets will accelerate aging, deterioration, and even burn.