A gasket is a mechanical seal between two objects, and if selected properly, it can usually effectively prevent material leakage between the two objects. Improper selection can result in unnecessary losses.
Today, we brought you the selection methods for flange gaskets. Let's learn together.
Sealing mechanism of flange gaskets
The leakage occurs when the medium flows through the interface between the inner and outer spaces is the leakage of the sealing surface. The fundamental cause of leakage is the presence of gaps on the contact surface, and the pressure and concentration differences on both sides of the contact surface are the driving force behind the leakage.
To reduce leakage, it is necessary to maximize the fitting of the contact surface, that is, to reduce the cross-sectional area of the leakage channel, increase the leakage resistance, and make it greater than the leakage driving force. Applying a compressive load to the sealing surface to generate a tightening force can improve the contact degree of the sealing surface.
When the stress increases enough to cause significant plastic deformation on the surface, it can fill the gap of the sealing surface and block the leakage channel.
The sealing mechanism of flange gasket static sealing can be divided into the following two situations.
1. Initial sealing
When assembling the flange gasket, the initial sealing can be completed by tightening the bolts and compressing the gasket. The basic condition for producing the initial sealing is to generate sufficient pressure between the sealing surfaces, that is, the pre-tightening stress of the gasket should cause the gasket material to undergo elastic compression deformation or elastic-plastic compression deformation after compression, which can fill the roughness and unevenness of the flange sealing surface, block the interface leakage channel, and achieve the initial sealing requirements. The pre-tightening stress of the gasket depends on the compression performance of the gasket material, and all sealing compression forces come from the initial tightening force of the bolt. At the same time, the flange should have sufficient strength and sufficient rigidity to prevent deflection or warping deformation.
2. Work seal
After pre-tightening the flange gasket bolt three component system, when subjected to the pressure of the working medium, the two sealing surfaces of a pair of flanges will be forced to separate relative to each other. At this time, the gasket should have sufficient rebound deformation to compensate for this separation. Not only that, the gasket also requires the ability to maintain sufficient residual gasket stress (compressive stress) at the sealing interface to ensure the sealing of the fluid medium.
Performance of flange gaskets
The main factors affecting flange sealing are as follows.
Pre-tightening force of bolts
Forms of sealing surface
Gasket performance
Flange stiffness
Operating conditions
The compression and rebound ability of the gasket is a necessary condition for flange sealing.
The deformation of gaskets includes two parts: elastic deformation and plastic deformation. Only elastic deformation has rebound ability. Gaskets with high rebound ability can better compensate for the separation of flange end faces, adapt to fluctuations in operating pressure and temperature, and thus have good sealing performance. The plastic deformation ability of the gasket surface is also very important, as it can effectively fill the micro-unevenness on the end face, thereby achieving initial sealing between flanges.
Selection of flange gaskets
The choice of gasket material mainly depends on the following three factors: temperature, pressure, and medium.
Basic principles for selecting gaskets
It has good compression and rebound performance, and can adapt to temperature and pressure fluctuations, good plasticity and can fit well with the flange sealing surface.
For certain metals with a tendency towards stress corrosion cracking (such as austenitic stainless acid resistant steel) flanges, it should be ensured that the gasket material does not contain excessive impurities that cause various types of corrosion, such as controlling the chloride ion content of the gasket to corrode the flange.
Non-polluting medium
For highly toxic chemicals that require sealing, gaskets should have greater safety.
For pipeline systems transporting flammable liquids, it is required that the maximum operating pressure and maximum operating temperature of gaskets used on flanges be within the limit range.
