Causes of leakage of sealing gaskets

I. Gasket mechanism　

Leakage that the medium from the inside of the finite space flow to the outside, or from the outside into the finite space inside. Media flow through the interface between the inner and outer space that is the sealing surface leakage occurs. The root cause of leakage is due to the existence of gaps on the contact surface, and the pressure difference between the two sides of the contact surface, the concentration difference is the driving force of leakage.　　

Due to the form of the leaking surface and processing accuracy and other factors, the existence of gaps on the sealing surface is inevitable, which will cause the sealing surface does not completely match, and thus leakage occurs. To reduce leakage, it is necessary to maximize the nesting of the contact surfaces, i.e., to reduce the cross-sectional area of the leakage channel, increase the leakage resistance, and make it greater than the leakage push force.　　

Applying a compressive load to the sealing surface to produce a compressive stress can increase the degree of contact between the sealing surfaces, and when the stress increases enough to cause significant plastic deformation of the surface, the gap between the sealing surfaces can be filled and the leak channel can be blocked.　

The purpose of using gaskets is to use the gasket material under the action of compressive load is more likely to produce plastic deformation characteristics, so that it fills the flange sealing surface of the small bump, so as to achieve sealing.

Second, the leakage form of gasket seal　　

In bolted flange gasket connection, gasket is the main sealing element. For non-metallic gaskets, the sealing of the connection is achieved by tightening the bolts, causing a large compressive stress on the contact surface of the flange and the gasket and the internal gasket, so that the gasket surface fits closely to the flange surface and fills the micro gap on the flange surface on the one hand, and reduces the porosity of the gasket material on the other hand, i.e., reduces the leakage channel of the sealed fluid.　　

Since no manufacturing or processing method can form an absolutely smooth ideal surface and achieve complete embedding between sealing surfaces and complete blockage of pores in the seal itself, there are always small gaps or channels between the sealing surfaces in contact with each other and inside the seal. Therefore, leakage is always inevitable for gasket seals. When the medium passes through the bolted flange connection at a certain pressure, there is always a leakage at the sealing point, which can be found in two forms, the so-called "interface leakage" and "permeation leakage". 1. Permeation leakage Non-metallic gaskets They are usually made of plant, animal, mineral or chemical fibers bonded and pressed with rubber, or made of porous materials such as flexible graphite. Due to its loose organization and poor denseness, there are countless tiny gaps between fibers and fibers, which can be easily penetrated by media, especially under pressure, the media will penetrate through the internal pores of the material. This phenomenon of leakage inside the gasket material is called "penetration leakage".　　

2、Interface Leakage Inadequate gasket compression stress, rough flange sealing surface, thermal deformation, mechanical deformation and vibration of the pipe can cause leakage between the gasket and flange sealing surface. In addition, the bolted flange connection can also cause leakage between the gasket and flange sealing surface due to temperature and pressure, bolt deformation and elongation, gasket creep and relaxation, reduction of resilience, aging and deterioration of the gasket material, etc. under operating conditions. This kind of leakage between the gasket and the flange sealing surface is called "interface leakage".