Types of gaskets

1. Types of gaskets

　　Common flange gaskets are divided into non-metallic gaskets, semi-metallic gaskets and metal gaskets according to their constituent materials.

　　(1) Non-metallic gaskets

　　Non-metallic gaskets are also called soft gaskets, mainly including asbestos rubber sheet gaskets, polytetrafluoroethylene coated gaskets, etc. Gaskets are mostly flat gaskets, and the operating pressure is not high, not higher than 5.0MPa. The operating temperature depends on the material of the gasket.

　　(2) Semi-metallic gaskets

　　Semi-metallic gaskets are composed of metal and non-metal materials, mainly including wound gaskets and metal coated gaskets. This type of gasket has good sealing performance and good pressure resistance. Wound gaskets can be used in harsh conditions of up to 25.0MPa and 600℃.

　　(3) Metal gaskets

　　Metal gaskets are made of metal (or alloy) materials through mechanical processing. Gasket types include flat gaskets, elliptical gaskets and octagonal gaskets. The material of the metal gasket is selected according to the corrosive properties and temperature of the medium, and specifically includes soft iron, alloy steel, copper, aluminum, etc. It is generally used in high-pressure situations, and the operating temperature depends on the selected material.

　　2. Principles for the selection of gaskets

　　(1) The selection of gaskets should be determined based on factors such as the sealing performance, operating pressure, operating temperature, working medium characteristics and sealing requirements of the gasket.

　　(2) Gasket material performance requirements

　　The gasket material performance should meet the following requirements:

　　① Have good physical and mechanical properties;

　　② Do not pollute the sealed medium, do not corrode the sealing surface, and resist corrosion from the working medium;

　　③ Have good compression and rebound properties;

　　④ Have a small stress relaxation rate;

　　⑤ Low leakage rate.

　　3. Selection of commonly used gaskets

　　(1) Asbestos rubber gaskets

　　Asbestos rubber gaskets are the most commonly used non-metallic gaskets, used for media such as water, steam, air and other inert gases with low temperature and pressure and small fluctuations. The maximum working temperature should be determined by the grade of asbestos rubber sheet used for the gasket, and the minimum operating temperature should not be lower than -50℃. When the medium is ethylene oxide, gaskets containing asbestos shall not be used; when operating under vacuum, asbestos rubber sheet gaskets are not allowed to be used; in situations where the medium does not allow trace fiber mixing, such as aviation gasoline or aviation kerosene, asbestos rubber sheet and other fiber gaskets should not be used.

　　Gaskets should comply with the current petrochemical industry standard "Asbestos rubber sheet gaskets for pipe flanges" SH 3401, chemical industry standard "Non-metallic flat gaskets for steel pipe flanges" HG 20606 (European system), HG 20627 (American system) and mechanical industry standard "Asbestos rubber sheet gaskets for pipeline flanges" JB/T 87 or equivalent standards.

　　(2) Flexible graphite composite gaskets

　　① The maximum working pressure of flexible graphite composite gaskets is 10.0MPa. The maximum working temperature depends on the metal core material. Depending on the core material, it can be selected between -196℃ and 650℃. Flexible graphite composite gaskets are suitable for various highly corrosive and permeable media such as water, oil, solvents, acids, alkalis, hydrogen, oil and gas, high-temperature flue gas, steam, etc.

　　② The gasket should comply with the current chemical industry standard "Flexible graphite composite gasket for steel pipe flanges" HG 20608 (European system), HG 20629 (American system) or equivalent standards.

　　(3) Polytetrafluoroethylene coated gasket

　　① Polytetrafluoroethylene coated gaskets are suitable for pipelines that are corrosion-resistant, anti-adhesive and require high cleanliness. The maximum nominal pressure should not exceed 5.0MPa and the maximum operating temperature is 150℃.

　　② The gasket should comply with the current petrochemical industry standard "Polytetrafluoroethylene coated gasket for pipe flange" SH 3402, the chemical industry standard "Polytetrafluoroethylene coated gasket for steel pipe flange" HG 20607 (European system) and HG 20628 (American system)

　　or the provisions of equivalent standards.

　　(4) Wound gasket

　　① Wound gasket is suitable for pipelines with highly toxic or flammable media or high temperature, large temperature difference, mechanical vibration or pressure pulsation.

　　② The selection of wound gaskets shall comply with the following provisions:

　　a. The flange of the convex surface shall adopt the wound gasket with outer ring;

　　b. The flange of the concave and convex surface shall adopt the wound gasket with inner ring;

　　c. The flange of the tongue and groove surface shall adopt the basic wound gasket;

　　d. The flange of the convex surface with nominal pressure equal to or greater than 15.0Mpa, the use of polytetrafluoroethylene wound gasket and the use of vacuum medium shall adopt the wound gasket with inner and outer ring.

　　③ The gasket shall comply with the current petrochemical industry standard "Wrapped gasket for pipe flange" SH 3407, the chemical industry standard "Wrapped gasket for steel pipe flange" HG 20610 (European system), HG 20631 (American system) and the mechanical industry standard "Wrapped gasket for pipeline flange" JB/T 90 or equivalent standards.

　　(5) Metal toothed combination gasket

　　① Metal toothed combination gaskets have the advantages of soft gaskets with low compression ratio and metal gaskets with good strength and elasticity. When having the same sealing effect, the bolt load is small and it is suitable for sealing medium, high pressure and high temperature pipeline flanges;

　　(6) Metal ring gasket

　　① Metal ring gaskets are suitable for high temperature and high pressure pipelines. The maximum temperature of use depends on the material used

　　② Gaskets should comply with the current petrochemical industry standard "Metal ring gaskets for pipe flanges" SH 3403, chemical industry standard "Metal ring gaskets for steel pipe flanges" HG 20612 (European system), HG 20633 (American system) and mechanical industry standard "Metal ring gaskets for pipeline flanges" JB/T 89 or equivalent standards;

　　③ The hardness value of the metal ring gasket material should be 30~40HB lower than the hardness value of the flange material.

　　(7) Metal sheathed gasket

　　① Metal sheathed gaskets have good sealing performance and are suitable for higher temperature media. Metal-clad gaskets can be made into gaskets with complex shapes. The most widely used are flat metal-clad gaskets;

　　③ The gaskets should comply with the current chemical industry standards "Metal-clad gaskets for steel pipe flanges" HG 20609 (European system) and HG 20630 (American system) or equivalent standards.