Gasket sealing mechanism
Leakage is the medium from the inside of a finite space to the outside, or from the outside into the inside of a finite space of people do not want to happen. Media flow through the interface between the internal and external space, that is, the sealing surface leakage. The root cause of leakage is the existence of a gap between the contact surface, while the pressure difference between the two sides of the contact surface, the concentration difference is the driving force of the leakage. Due to the form of the sealing surface and processing accuracy and other factors, resulting in the sealing surface does not completely match, that is, the sealing surface will appear on the gap, and thus leakage occurs. To reduce leakage, it is necessary to maximise the embedding of the contact surfaces, i.e. to reduce the cross-sectional area of the leakage channel and increase the resistance to leakage so that it is greater than the leakage driving force. Apply compressive load on the sealing surface can produce compressive stress, improve the degree of contact of the sealing surface, when the stress increases enough to cause significant plastic deformation of the surface, it can fill the gap between the sealing surface, in order to block the leakage channel. The purpose of using gaskets is to fill the small unevenness of the sealing surface of the flange with the help of the gasket material that is easier to produce plastic deformation under the action of compression load, so as to realise the sealing.
In flange sealing joints, the force of the compression gasket deforms the gasket material, thus filling the micro-gap between the flange sealing surfaces.
Forms of leakage in gasket sealed joints
In flange sealing joints, the gasket is the main sealing element. For non-metallic gaskets, the sealing of the connection is made by tightening the bolts, causing the flange and the gasket contact surface and the gasket internal larger compressive stress, on the one hand, make the gasket surface and the flange surface close to the flange surface, fill up the flange surface of the microgap, on the other hand, reduce the porosity of the gasket material, i.e., reduce the leakage channel of the fluid being sealed. As any processing method is not possible to form an absolutely smooth ideal surface, it is also impossible to achieve the sealing surface between the completely embedded and the seal itself pore completely blocked, so in contact with each other between the sealing surfaces and seals of the internal always exists a small gap or channel. Thus, for gasket sealing, leakage is always inevitable. When the medium at a certain pressure through the bolt - flange connection, always in the sealing point at the leakage. Analysis of this phenomenon can be found, the leakage is in two forms, namely, "interface leakage" and "penetration leakage", as shown in Figure 2.
1. Interface leakage
Insufficient gasket compression stress, flange sealing surface roughness, thermal deformation, mechanical deformation and vibration of the pipeline will cause the gasket and the flange sealing surface between the poor fit and leakage. In addition, the flange joint in the operating conditions due to temperature, pressure, bolt deformation and elongation, gasket creep relaxation, rebound capacity decline, gasket material aging, deterioration, etc. will also cause leakage between the flange and flange sealing surface. This happens in the gasket and flange sealing surface between the leakage is called "interface leakage".
2. Penetration leakage
Non-metallic gaskets are usually made of plant fibres, animal fibres, mineral fibres or chemical fibres and rubber bonded and pressed, or made of porous materials such as flexible graphite. Because of its loose tissue, poor densification, there are countless tiny gaps between the fibres and fibres, so it is easy to be soaked by the medium, especially under pressure, the medium will be penetrated through the pores within the material. This happens in the gasket material inside the leakage is called "penetration leakage".
