Gasket Sealing Mechanisms
Leakage is the unwanted phenomenon of media flowing from the inside of a finite space to the outside, or from the outside into the inside of a finite space. Leakage occurs when the medium flows through the interface between the inner and outer space, i.e. the sealing surface. The root cause of leakage is the existence of a gap in the contact surface, while 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 sealing surface and processing accuracy and other factors, resulting in the sealing surface does not exactly match, i.e. there will be a gap on the sealing surface, and thus leakage occurs. To reduce leakage, it is necessary to maximise the nesting of the contact surfaces, i.e. to reduce the cross-sectional area of the leakage path and increase the leakage resistance so that it is greater than the leakage push. A compressive load applied to the sealing surface can produce a compressive stress that increases the degree of contact between the sealing surfaces, and when the stress increases enough to cause significant plastic deformation of the surface, the gap in the sealing surface can be filled to plug the leak path. The purpose of using gaskets is to use the gasket material under the action of compressive load is easier to produce plastic deformation characteristics, so that it fills the flange sealing surface of the small bump, so as to achieve sealing.
In a flange sealed joint, the force of the compression gasket deforms the gasket material to fill the micro gap between the flange sealing surfaces.
Forms of leakage in gasket sealed joints
In flange sealed joints, the gasket is the main sealing element. In the case of non-metallic gaskets, the connection is sealed by tightening the bolts, causing a large compressive stress on the contact surface between the flange and the gasket and inside the gasket, which on the one hand makes the gasket surface fit closely to the flange surface and fills the micro-gap on the flange surface, and on the other hand reduces the porosity of the gasket material, i.e. reduces the leakage channel of the fluid being sealed. Since it is not possible to form an absolutely smooth ideal surface by any processing method, nor is it possible to achieve a complete nesting between the sealing surfaces and a complete blockage of the pores of the seal itself, there are always small gaps or channels between the sealing surfaces in contact with each other and inside the seal. As a result, leakage is always inevitable for gasket seals. When a medium passes through a bolt-flange connection at a certain pressure, there is always a leak at the sealing point. Analysis of this phenomenon reveals that leakage occurs in two forms, namely "interface leakage" and "permeation leakage".
1. Interfacial leakage
Insufficient gasket compressive stress, rough flange sealing surface, thermal deformation, mechanical deformation and vibration of the pipe can cause leakage due to poor fit between the gasket and flange sealing surface. In addition, flange joints in operating conditions due to the role of temperature, pressure, bolt deformation elongation, gasket creep relaxation, resilience, gasket material aging, deterioration, etc. will also cause leakage between the flange and flange sealing surface. This kind of leakage between the gasket and the flange sealing surface is called "interface leakage".
2. Penetration Leakage
Non-metallic gaskets are usually made of plant, animal, mineral or chemical fibres bonded to rubber, or made of porous materials such as flexible graphite. Due to its loose organization, poor denseness and numerous tiny gaps between fibres, it is easily penetrated by media, especially under pressure, through the internal pores of the material. This kind of leakage occurs inside the gasket material and is called "leakage by penetration".
