The basic concept of gasket sealing

A gasket seal is the most important sealing structure form of detachable joints such as pressure vessels, process equipment, power machines, and connecting pipes in industrial equipment, which is usually composed of flanges, gaskets, and connecting bolts and nuts, collectively known as flange sealing joints.

Gasket sealing mechanism

Leakage is the phenomenon that the medium flows from the inside of the limited space to the outside, or the people who enter the inside of the limited space from the outside do not want to happen. The medium flows through the interface of the inner and outer space, that is, the sealing surface leaks. The root cause of leakage is that there is a gap in the contact surface, and the pressure difference and concentration difference on both sides of the contact surface are the driving force of leakage. Due to the influence of factors such as the form of the sealing surface and processing accuracy, the sealing surface is not completely matched, that is, there will be a gap on the sealing surface, resulting in leakage. To reduce leakage, it is necessary to maximize the contact surface, that is, to reduce the cross-sectional area of the leakage channel, and increase the leakage resistance so that it is greater than the leakage driving force. Applying compressive load to the sealing surface can produce compressive stress and improve the contact degree of the sealing surface. When the stress increases enough to cause obvious plastic deformation on the surface, the gap of the sealing surface can be filled to block the leakage channel. The purpose of using a gasket is to make use of the characteristics of gasket material that is easier to produce plastic deformation under the action of compression load, so as to fill the small uneven flange sealing surface, so as to achieve sealing. In the flange sealing joint, the force of pressing the gasket deforms the gasket material, thus filling the micro gap between the flange sealing surfaces.

The gasket seals the leakage form of the connection

In the flange sealing joint, the gasket is the main sealing element. For non-metallic gaskets, the sealing of the connection is by tightening the bolt, resulting in large compression stress between the flange and the gasket contact surface and the gasket inside the gasket, on the one hand, the gasket surface and the flange surface are closely fitted to fill the micro gap on the flange surface, on the other hand, the porosity of the gasket material is reduced, that is, the leakage channel of the sealed fluid is reduced. Because any processing method can not form an absolutely smooth ideal surface, nor can it achieve complete chimerism between the sealing surface and the complete obstruction of the pores of the seal itself, there are always small gaps or channels between the sealing surface and the inside of the seal. Therefore, for gasket seals, leakage is always inevitable. When the medium is connected through the bolt flange at a certain pressure, there will always be leakage at the sealing point. By analyzing this phenomenon, it can be found that leakage occurs in two forms, namely "interface leakage" and "infiltration leakage".

1. The interface leaks

The gasket compression stress is insufficient, the flange sealing surface is rough, and the thermal deformation, mechanical deformation and vibration of the pipeline will cause the fitting between the gasket and the flange sealing surface to be lax and cause leakage. In addition, the flange joint under operating conditions due to the role of temperature and pressure, bolt deformation and elongation, gasket creep relaxation, decline in rebound ability, gasket material aging, deterioration, etc., will also cause leakage between the flange and the flange sealing surface. This leakage between the gasket and the flange sealing surface is called "interface leakage".

2. Infiltration and leakage

Non-metallic gaskets are usually made of plant fiber, animal fiber, mineral fiber, or chemical fiber bonded with rubber or made of porous materials such as flexible graphite. Due to its loose organization and poor density, there are countless tiny gaps between the fibers and the fibers, so it is easy to be soaked by the medium, especially under pressure, the medium will penetrate through the pores inside the material. This leakage, which occurs inside the gasket material, is called "infiltration leakage".