How to Select Gaskets?
How to Select Gaskets?
Here are five elements of the gasket selection. If you understand them, the gasket selection is not difficult for you.
Gaskets and gasket seals
A gasket is a material or combination of materials clamped between two independent connectors (mainly referring to flanges), whose function is to maintain the seal between the two connectors within the predetermined service life.
The gasket must be able to seal the joint surface and ensure that the sealing medium is not permeable or corroded. It can withstand the effects of temperature and pressure. The gasket seal generally consists of connectors (such as flanges), gaskets, and fasteners (such as bolts and nuts). Therefore, when determining the sealing performance of a certain flange, the entire flange connection structure must be considered as a system. The normal operation or failure of the gasket depends not only on the performance of the gasket itself in the design, but also on the stiffness and deformation of the system, the roughness and parallelism of the joint surface, and the size and uniformity of the fastening load.
Five Elements of the Selection of Gaskets
Temperatures
The selected gasket should have a reasonable service life at the highest or lowest working temperature, and the maximum working temperature varies greatly among different gasket materials.
In addition to the maximum and minimum working temperatures that can be tolerated in the short term, the allowable continuous working temperature should also be considered. The gasket material should be able to resist creep to reduce the stress relaxation of the gasket, so as to ensure the sealing of the gasket under working conditions. Most gasket materials will experience severe creep as the temperature increases. Therefore, an important indicator of the quality of the gasket is its creep relaxation performance at a certain temperature.
Applications
It mainly refers to the information of the connection system where the gasket is located, and the appropriate gasket material and type need to be selected based on the material of the flange, the sealing surface type of the flange, the roughness of the flange, and bolt information.
Non-metal flanges must choose gaskets with relatively low pre tightening force requirements, otherwise it is likely that during the flange tightening process, the gasket has not been compressed yet and the flange has been crushed.
For different flange sealing surface types, the corresponding gasket types are also different. For example, the spiral wound gasket type corresponding to the raised face flange (RF) is a spiral wound gasket with inner and outer rings, the spiral wound gasket type corresponding to the tenon groove surface (TG) flange is a basic spiral wound gasket. The spiral wound gasket type corresponding to the concave convex surface (MFM) flange is a spiral wound gasket with only inner rings.
Different gaskets also have different requirements for flange roughness.
The gasket should not be affected by the sealing medium throughout the working conditions, including high temperature oxidation resistance, chemical corrosion resistance, solvent resistance, permeability resistance, etc. Obviously, the chemical corrosion resistance of the gasket material to the medium is the primary condition for selecting a gasket. For non-metallic gaskets or non-metallic materials in composite gaskets, the chemical corrosion resistance of the materials can refer to the non-metallic material chemical resistance performance table provided by the gasket manufacturer. For metal materials in direct contact with the medium in the gasket, they should have the same or higher corrosion resistance as flange materials.
Pressure
The gasket must be able to withstand the maximum pressure, which may be the test pressure, which may be 1.25 to 1.5 times the normal working pressure. For non-metallic gaskets, their maximum pressure is also related to the maximum working temperature. Usually, the value of the highest temperature multiplied by the highest pressure (i.e. PxT value) has a limit value. Therefore, when selecting their maximum working pressure, the maximum PxT value that the gasket can withstand should also be considered. The following figure shows the PxT values of common pressed gaskets in GARLOCK, and the pressure that different types of gaskets can withstand varies.
When meeting the conditions of flange roughness and unevenness, choose thin gaskets as much as possible. The thickness of the gasket is related to its type, material, diameter, processing condition of the sealing surface, and sealing medium. For most non-metallic sheet gaskets, thin gaskets also have a greater ability to resist stress relaxation. Due to the small contact area between the inner side of the thin gasket and the medium, the leakage along the gasket body is also reduced. In this case, the blowing force borne by the gasket is also small, making it difficult for the gasket to be blown out. The anti-blowing ability of the thin gasket is stronger than that of the thick gasket. Of course, you can also refer to the gasket standard to choose gasket thickness and other dimensions.
In addition, due to the fact that gaskets usually use bolt flange connection structures, it is necessary to pre tighten the bolts to meet the sealing requirements during assembly. In addition, the gasket in this structure is a sealing element affected by many factors, so how to control the pre tightening force is a very difficult problem. The required compression load for various gaskets is also different. For gasket seals with special requirements, there are no standard connection dimensions, such as flange thickness, bolt size, bolt spacing, etc., which requires special design considerations.
In addition, due to the fact that gaskets usually use bolt flange connection structures, it is necessary to pre tighten the bolts to meet the sealing requirements during assembly. In addition, the gasket in this structure is a sealing element affected by many factors, so how to control the pre tightening force is a very difficult problem. The required compression load for various gaskets is also different. For gasket seals with special requirements, there are no standard connection dimensions, such as flange thickness, bolt size, bolt spacing, etc., which requires special design considerations.
Here are five elements of the gasket selection. If you understand them, the gasket selection is not difficult for you.
Gaskets and gasket seals
A gasket is a material or combination of materials clamped between two independent connectors (mainly referring to flanges), whose function is to maintain the seal between the two connectors within the predetermined service life.
The gasket must be able to seal the joint surface and ensure that the sealing medium is not permeable or corroded. It can withstand the effects of temperature and pressure. The gasket seal generally consists of connectors (such as flanges), gaskets, and fasteners (such as bolts and nuts). Therefore, when determining the sealing performance of a certain flange, the entire flange connection structure must be considered as a system. The normal operation or failure of the gasket depends not only on the performance of the gasket itself in the design, but also on the stiffness and deformation of the system, the roughness and parallelism of the joint surface, and the size and uniformity of the fastening load.
Five Elements of the Selection of Gaskets
Temperatures
The selected gasket should have a reasonable service life at the highest or lowest working temperature, and the maximum working temperature varies greatly among different gasket materials.
In addition to the maximum and minimum working temperatures that can be tolerated in the short term, the allowable continuous working temperature should also be considered. The gasket material should be able to resist creep to reduce the stress relaxation of the gasket, so as to ensure the sealing of the gasket under working conditions. Most gasket materials will experience severe creep as the temperature increases. Therefore, an important indicator of the quality of the gasket is its creep relaxation performance at a certain temperature.
Applications
It mainly refers to the information of the connection system where the gasket is located, and the appropriate gasket material and type need to be selected based on the material of the flange, the sealing surface type of the flange, the roughness of the flange, and bolt information.
Non-metal flanges must choose gaskets with relatively low pre tightening force requirements, otherwise it is likely that during the flange tightening process, the gasket has not been compressed yet and the flange has been crushed.
For different flange sealing surface types, the corresponding gasket types are also different. For example, the spiral wound gasket type corresponding to the raised face flange (RF) is a spiral wound gasket with inner and outer rings, the spiral wound gasket type corresponding to the tenon groove surface (TG) flange is a basic spiral wound gasket. The spiral wound gasket type corresponding to the concave convex surface (MFM) flange is a spiral wound gasket with only inner rings.
Different gaskets also have different requirements for flange roughness.
The gasket should not be affected by the sealing medium throughout the working conditions, including high temperature oxidation resistance, chemical corrosion resistance, solvent resistance, permeability resistance, etc. Obviously, the chemical corrosion resistance of the gasket material to the medium is the primary condition for selecting a gasket. For non-metallic gaskets or non-metallic materials in composite gaskets, the chemical corrosion resistance of the materials can refer to the non-metallic material chemical resistance performance table provided by the gasket manufacturer. For metal materials in direct contact with the medium in the gasket, they should have the same or higher corrosion resistance as flange materials.
Pressure
The gasket must be able to withstand the maximum pressure, which may be the test pressure, which may be 1.25 to 1.5 times the normal working pressure. For non-metallic gaskets, their maximum pressure is also related to the maximum working temperature. Usually, the value of the highest temperature multiplied by the highest pressure (i.e. PxT value) has a limit value. Therefore, when selecting their maximum working pressure, the maximum PxT value that the gasket can withstand should also be considered. The following figure shows the PxT values of common pressed gaskets in GARLOCK, and the pressure that different types of gaskets can withstand varies.
When meeting the conditions of flange roughness and unevenness, choose thin gaskets as much as possible. The thickness of the gasket is related to its type, material, diameter, processing condition of the sealing surface, and sealing medium. For most non-metallic sheet gaskets, thin gaskets also have a greater ability to resist stress relaxation. Due to the small contact area between the inner side of the thin gasket and the medium, the leakage along the gasket body is also reduced. In this case, the blowing force borne by the gasket is also small, making it difficult for the gasket to be blown out. The anti-blowing ability of the thin gasket is stronger than that of the thick gasket. Of course, you can also refer to the gasket standard to choose gasket thickness and other dimensions.
In addition, due to the fact that gaskets usually use bolt flange connection structures, it is necessary to pre tighten the bolts to meet the sealing requirements during assembly. In addition, the gasket in this structure is a sealing element affected by many factors, so how to control the pre tightening force is a very difficult problem. The required compression load for various gaskets is also different. For gasket seals with special requirements, there are no standard connection dimensions, such as flange thickness, bolt size, bolt spacing, etc., which requires special design considerations.
In addition, due to the fact that gaskets usually use bolt flange connection structures, it is necessary to pre tighten the bolts to meet the sealing requirements during assembly. In addition, the gasket in this structure is a sealing element affected by many factors, so how to control the pre tightening force is a very difficult problem. The required compression load for various gaskets is also different. For gasket seals with special requirements, there are no standard connection dimensions, such as flange thickness, bolt size, bolt spacing, etc., which requires special design considerations.