Whether for pressure vessels, process equipment, power machinery, or connecting pipelines, gaskets play a crucial role as the key component that prevents liquid or gas leakage. However, as production facilities become larger and processes develop toward high temperature, high pressure, and high speed, the risk of leakage continues to increase. Once leakage occurs, it not only leads to production interruption and economic losses but may also cause fires, explosions, and other major accidents, resulting in casualties and environmental pollution. Therefore, correctly selecting a suitable gasket is essential for ensuring production safety and efficiency.
A gasket is a material or combination of materials clamped between two separate connecting parts (mainly flanges), whose main function is to maintain a seal between the two connection parts within the predetermined service life. The gasket must be able to seal the joint surface, ensure that the sealed medium does not penetrate or corrode, and withstand the effects of temperature and pressure. The gasket sealing system usually consists of connecting parts (such as flanges), gaskets, and fasteners (such as bolts and nuts). Therefore, when evaluating flange sealing performance, the entire flange connection structure must be considered as a system.
Selecting the right gasket is by no means an easy task, especially in complex industrial environments, where multiple factors must be comprehensively considered. These factors not only include basic parameters such as temperature, medium, and pressure but also involve details such as flange type, gasket material, and thickness. Only by comprehensively considering these factors can the gasket achieve optimal performance in actual applications, effectively prevent leakage, and ensure production safety.
Temperature is the primary consideration when selecting a gasket. The maximum working temperature of gasket materials varies greatly, so it must be ensured that the selected gasket can maintain a reasonable service life at the highest or lowest operating temperature. In addition to the short-term maximum and minimum operating temperatures, the permissible continuous working temperature should also be considered. For example, when the system operating temperature is close to the maximum continuous operating temperature of the gasket material, a higher-grade material should be selected.
The gasket must resist the influence of the sealed medium, including resistance to high-temperature oxidation, chemical corrosion, solvent, and permeability. The chemical corrosion resistance of the gasket material to the medium is the primary condition for gasket selection. For non-metallic gaskets or the non-metallic part of composite gaskets, reference can be made to the chemical resistance table of non-metallic materials provided by the gasket manufacturer. The metallic materials that are in direct contact with the medium should have corrosion resistance equal to or higher than that of the flange material.
The gasket must withstand the maximum pressure, which may be the test pressure, usually 1.25–1.5 times the normal working pressure. For non-metallic gasket materials, the maximum pressure also relates to the maximum operating temperature, and the product of maximum temperature and maximum pressure (PxT value) has a limiting value. Therefore, when selecting the maximum working pressure, the maximum PxT value the gasket can withstand should also be considered.
The selection of a gasket also needs to comprehensively consider the material of the flange, the type of sealing face, roughness, and bolt information. Different types of flanges require different types of gaskets. For example, raised face (RF) flanges usually use spiral wound gaskets with inner and outer rings, tongue and groove (TG) flanges use basic type spiral wound gaskets, while male and female (MFM) flanges use spiral wound gaskets with only inner rings. In addition, non-metallic flanges must choose gaskets requiring smaller pre-tightening force to avoid the situation where the gasket is not fully compressed while the flange is already crushed during tightening.
The gasket thickness is related to its type, material, diameter, the machining condition of the sealing surface, and the sealing medium. Under the conditions of meeting flange roughness and unevenness, thinner gaskets should be selected as much as possible. Thin gaskets have greater resistance to stress relaxation, smaller contact area with the medium on the inner side, reduced leakage along the gasket body, smaller blowout force, and stronger blowout resistance.
In modern industrial applications, there are many types of gaskets, each with its own unique performance and applicable scenarios. Selecting the right gasket requires consideration not only of its material characteristics but also of the actual operating conditions. The following are several common types of gaskets and their characteristics.
Flexible graphite gaskets have good high-temperature resistance and can maintain stable sealing performance under extreme temperatures. They also have good chemical corrosion resistance and impermeability, suitable for various media. Flexible graphite gaskets are relatively thin, have strong resistance to stress relaxation, and are ideal choices for high-temperature and high-pressure environments.
Polytetrafluoroethylene (PTFE) gaskets are well known for their excellent chemical stability and corrosion resistance. They can resist corrosion by most chemical media and are suitable for various industrial applications. PTFE gaskets also have good impermeability and can effectively prevent fluid leakage. However, their high-temperature resistance is relatively weak, and they are generally suitable for medium- and low-temperature environments.
Rubber gaskets are common non-metallic gaskets with good elasticity and compressibility. They can adapt to slight unevenness of flange surfaces and provide good sealing performance. The temperature and chemical corrosion resistance of rubber gaskets are relatively weak, so they are usually suitable for low-temperature, low-pressure, and weakly corrosive media environments.
With the increasing awareness of environmental protection and health, asbestos gaskets have been gradually phased out, and non-asbestos fiber gaskets have become the substitute. This type of gasket has good chemical corrosion resistance and impermeability while avoiding the health risks caused by asbestos. Non-asbestos fiber gaskets are suitable for various media and environments and are environmentally friendly sealing materials.
Spiral wound gaskets are composed of alternating layers of metal strips and non-metallic fillers, having good elasticity and sealing performance. They can adapt to flange surface irregularities and provide reliable sealing. Spiral wound gaskets are available in various types, such as inner and outer ring type, basic type, and inner ring only type, and the appropriate model can be selected according to the flange sealing surface type. Spiral wound gaskets are suitable for various media and working conditions and are widely used sealing materials.
Metal composite gaskets are composed of metal and non-metallic materials, combining the strength of metal with the sealing performance of non-metallic materials. This type of gasket has excellent high-temperature, high-pressure, and chemical corrosion resistance and is suitable for high-temperature and high-pressure environments. Types of metal composite gaskets include corrugated gaskets, oval gaskets, and octagonal gaskets, and appropriate types can be selected according to specific applications.
Selecting a suitable gasket is a complex process that requires comprehensive consideration of various factors. The following are detailed selection steps to help you make the correct choice in practical applications.
Temperature: Determine the highest and lowest operating temperatures of the system and the permissible continuous operating temperature.
Medium: Determine the corrosiveness, oxidizing property, and permeability of the fluid, and refer to the chemical resistance table provided by the gasket manufacturer.
Pressure: Determine the maximum operating pressure of the system, including test pressure and normal operating pressure.
Flange Information: Determine the material of the flange, type of sealing face, roughness, and bolt information.
According to the operating parameters, select the appropriate gasket material. For high-temperature and high-pressure systems, metal composite or metal gaskets can be selected; for medium- and low-pressure systems, non-metallic soft gaskets or spiral wound gaskets can be chosen.
Select the appropriate gasket type according to the flange sealing face type. For example, raised face (RF) flanges use spiral wound gaskets with inner and outer rings, tongue and groove (TG) flanges use basic type spiral wound gaskets, and male and female (MFM) flanges use spiral wound gaskets with inner rings only.
Under the conditions of meeting flange roughness and unevenness, thinner gaskets should be selected as much as possible. Thin gaskets have greater resistance to stress relaxation and stronger blowout resistance.
Preload: Calculate the effective load according to bolt size, quantity, and grade to ensure that the gasket can meet the sealing requirements.
System Stability: Consider the influence of pressure fluctuation, temperature change, bolt preload relaxation, flange tilt, or misalignment on sealing performance.
Cleaning and Maintenance: Consider system cleaning and maintenance to prevent cleaning fluid from corroding the gasket.
Gasket sealing occupies an extremely important position in modern industrial enterprises. Correct selection and installation of gaskets are crucial to ensuring production continuity, property safety, energy conservation, environmental protection, and human health. Choosing a suitable gasket requires comprehensive consideration of multiple factors such as temperature, medium, pressure, and flange information, and selecting appropriate gasket materials and types according to actual working conditions. At the same time, correct installation methods are also the key to ensuring sealing performance. Through the above introduction, it is hoped that you can better understand and master the key points of gasket selection and installation, ensuring safe and efficient operation of your industrial equipment.