The gasket is the main seal of the flange connection, so the correct use of the gasket is also the key to ensure that the flange connection does not leak. Depending on the material, the gasket can be divided into many types. In addition to the type of gasket, the identification and selection of the gasket are also important! 

 1 Structural type of gasket 

 Flat gaskets used in industry are generally composed of sealing elements and inner and outer reinforcement rings. Sealing elements or gasket bodies are key parts to prevent leakage. Its commonly used materials are non-metallic materials, such as flexible graphite, polytetrafluoroethylene, fiber-reinforced rubber-based composite plates, etc. In addition, the sealing element material can also be rigid or flexible metal, which is usually used in situations with high pressure and temperature. For sealing elements of non-metallic materials, metal materials are usually inserted to strengthen, and it also facilitates the manufacturing and processing of sealing elements of fragile materials such as graphite. Reinforced materials can be metal sheet metal sheet or wire mesh. Metal sheet metal sheet often uses a punch hole to enhance the effect and increase elasticity, and binds them together through binders and roller pressure. Sealing elements can also be set up with a surface layer or anti-bonding treatment layer to increase the sealing effect and prevent the flange sealing surface from bonding. 

 Outer reinforcement rings or outer ring materials are solid metals, and their functions are: 

 Help fit the sealing element when installing; 

 Prevent the sealing element from being damaged by excessive compression; prevent the gasket from blowing out and reduce flange rotation, etc. 

 The outer reinforcement ring does not come into contact with the sealing medium, so it does not require resistance to medium corrosion, so it is often made of carbon steel. The outer reinforcement ring can also be integrated with sealing elements, such as metal tooth gaskets and wave-tooth composite gaskets. 

 The inner reinforcement ring or inner ring comes into contact with the fluid, and its material should be able to resist corrosion by the sealing medium. The function of the inner reinforcement ring is: 

 Prevent the gap between the sealing element and the vessel or pipe flange to avoid interfering with the flow of fluid and the impact of the resulting fluid on the gasket. 

2 Types of flange gaskets 

 1. Non-metallic flat gasket - PTFE-wrapped gasket 

 1Introduction to the gasket 

 PTFE bag gasket is a kind of non-metallic composite soft gasket, which generally consists of two parts: the envelope and the insert. The envelope is mainly corrosion-resistant, usually made of polytetrafluoroethylene material, and the insert (filler) is a non-metallic material with or without metal reinforcement, usually made of asbestos rubber plate. 

 PTFE-wrapped gaskets are mainly suitable for all-planar and protube flange connections, and are suitable for corrosive media with a nominal pressure of PN of 0.6-5.0MPa and a working temperature of 0-150 ℃ or a medium with high requirements for cleanliness. 

 2 form of gaskets 

 PTFE-wrapped gaskets for pipe flanges can be divided into three types according to the manufacturing method: cut type (S type), machined type (M type), and folded package type (F type). 

 For machined wrapping gaskets, the inner diameter of the wrapping layer can be consistent with the inner diameter of the flange to prevent fluid from generating eddy currents at the flange. For the folded bag gasket, it is a ribbon-like PTFE film with a thickness of 0.4~0.8mm. The two ends are heated together and wrapped in a U-shape on the outside of the ring-shaped core material, which is easy to manufacture and suitable for large-sized flange sealing. 

 3 Marking - Marking Example 

 Cut-off polytetrafluoroethylene gasket with a nominal diameter of 50mm and a nominal pressure of 1.0MPa: 

 S-50-1.0 GB/T1304-1992 

 Machined PTFE gasket with a nominal diameter of 50mm and a nominal pressure of 1.0MPa: 

 M-50-1.0 GB/T1304-1992 

 Folding polytetrafluoroethylene gasket with a nominal diameter of 50mm and a nominal pressure of 1.0MPa: 

 F-50-1.0 GB/T1304-1992 

 2. Metal composite gasket 

 (1) Metal winding gasket 

 Metal winding gasket is a semi-metal flat gasket made of spiral composite winding of metal belts and non-metallic belts. 

 1 The characteristics of the metal winding gasket are: 

 Good compression and resilience; 

 It has multiple sealing and a certain self-tightening function; 

 It is not sensitive to the surface defects of the flange compression surface, and does not adhere to the flange sealing surface, which is easy to slit, so it is easy to disassembling; 

 It can partially eliminate the effects of pressure, temperature changes and mechanical vibration; 

 It can maintain its excellent sealing performance under various cyclical conditions such as high temperature, low pressure, high vacuum, shock vibration, etc. 

 2 form 

 The winding gasket can be divided into four types according to its structure: basic type, with inner ring type, belt designated as ring type, with inner ring and designated as ring type. 

 3 pad type code (GB/T4622.1-2003) 

 4 Marking - Marking Example 

 With inner ring and designated as a ring type: 

 The ring material is made of low-carbon steel and the metal strip material is 0Cr18Ni9; 

 Nominal diameter 150mm; 

 Nominal pressure 4.0MPa (40bar); 

 G垫 size standard GB/T4622.2-2003; 

 It is marked as: 

 Winding pad D 1222-DN150-PN40 GB/T4622.2 

 Basic type: 

 The metal belt material is 0Cr18Ni9, and the filling belt material is flexible graphite; 

 Nominal diameter 150mm; 

 Nominal pressure 4.0MPa (40bar); 

 G垫 size standard GB/T4622.2-2003; 

 It is marked as: 

 Winding pad A 0220-DN150-PN40 GB/T4622.2 

 5 Selection and use of winding gaskets: 

 A. The basic gasket is suitable for tenon groove flange 

 B. Inner ring gasket is suitable for concave and convex flanges 

 C. Ring-shaped shim is suitable for flat and protuberant flanges 

 D. Inner rings and ring gaskets are suitable for flat and protuberant flanges 

 (2) Metal cling gasket 

 1 structure 

 Metal wrap gasket is a composite gasket made of non-metallic material as the core material, cut into the desired shape, and the outer bread is composed of metal sheets with a thickness of 0.25-0.5mm. Depending on the state of the bag, it is generally divided into two types: flat type and rve type. 

 According to the structural type, it is divided into two types: flat type (F type) and bellow type (type C). The structural type of metal-wrap gasket for pressure vessel flange is flat. 

 2Metal standard and code (JB/T4706-2000) 

 3 Marking - Marking Example 

 Correl metal bag gasket with nominal diameter 50mm and nominal pressure 2.0MPa: C-50-2.0 GB/T15601 

 Marks and examples of metal-wrapped gaskets for pressure vessel flanges: 

 Package gasket with a nominal diameter of 1000mm, a nominal pressure of 2.50MPa, and a metal plate of 0Cr18Ni9: 

 G-1000-2.50-JB/T4706-2000 

 (3) Metal punch plate flexible graphite composite gasket 

 1Introduction to the gasket 

 This gasket, also known as flexible graphite metal-reinforced composite gasket, is a sealing gasket made of punched metal tooth plate or punched metal core plate combined with flexible graphite particles. It is usually made from flexible graphite composite reinforced plate. 

 Flexible graphite metal reinforced composite gaskets can be made into inner edges or inner outer edges with stainless steel or carbon steel as needed. 

 2 features 

 The main characteristics are: good resistance to high and low temperatures, corrosion resistance, radiation resistance, etc., high strength, and can be used under high pressure conditions. The required preload is smaller than using metal gaskets or metal winding gaskets. Due to its plasticity and good filling properties, flexible graphite does not require precision machining on the matching flange sealing surface when using this gasket, and it is relatively economical to adapt to the flange sealing surface with "waterline" grooves. 

 Flexible graphite composite gasket types are divided into RF type, MFM type and TG type, which are suitable for protuberance, concave and convex surface and tenon groove flanges respectively. As needed, RF type gaskets can be wrapped with stainless steel or carbon steel inner edges, which is RF-E type. 

 3 Marking - Marking Example 

 Flexible graphite metal reinforced composite gasket for tenon flange with nominal diameter 100mm, nominal pressure 2.5MPa, core material is low-carbon steel: 

 HG/T 20608 Graphite Composite Pad TG 100-2.5 St 

 Flexible graphite metal reinforced composite gasket with nominal diameter 200mm, nominal pressure 4.0MPa, core plate material 0Cr18Ni9 for protuberance: 

 HG/T 20608 Graphite Composite Pad RF-E 200-4.0 304 

 (4) Metal wave tooth composite gasket 

 1Introduction to the gasket 

 The metal tooth composite gasket made of flexible graphite is a composite gasket that is mechanically processed into a tooth-shaped metal plate coated with flexible graphite on both sides. This gasket has both metal strength and ragged elasticity, with a maximum temperature of 650℃ and a maximum pressure of 26MPa. 

 2 type of gasket 

 Flexible graphite metal wave tooth composite gaskets are divided into three types according to their different structures: basic type, with positioning type, and with spacer type. 

 G垫 type code (GB/T19066.1-2003) 

 3Marking-Marking Method: 

 With positioning ring type: 

 Metal skeleton material 0Cr18Ni9; 

 Nominal diameter 150mm; 

 Nominal pressure 4.0MPa (40bar); 

 G垫 size standard GB/T19066.2. 

 Metal skeleton material code (GB/T19066.1-2003) 

 Wave tooth pad: 

 B3-DN150-PN40 GB/T19066.2 

 3. Metal gasket 

 (1) Metal ring gasket 

 Metal ring gasket is a solid metal gasket processed from metal material into an ocagonal or elliptical section, which has a radial self-tightening effect. Therefore, the metal ring gasket is in contact with the inner and outer sides (mainly the outer side) of the flange groove and is sealed by pressing. 

 The ocagonal ring pad is matched with the flange groove and is mainly manifested as surface contact. Compared to the oval ring pad, although it is not easy to close with the flange groove, it can be used again, and because the cross-section is made of a straight line, it is easy to process. The oval ring pad is in contact with the flange groove and has good sealing, but the processing accuracy is required, which increases manufacturing costs. At the same time, the oval ring pad cannot be reused. 

 The nominal pressure applicable to metal ring pads is 2.0 to 42.0 MPa. 

 (2) Metal toothed gasket 

 1Introduction to the gasket 

 Metal tooth gasket is a solid metal gasket. The section of the gasket is serrated, the tooth spacing t=1.5～2mm, the tooth height h=0.65～0.85mm, and the top width C=0.2～0.3mm. Several concentric circles are turned on the sealing surface, and the number of teeth is 7-16, depending on the size of the gasket. 

 2 Structural form and advantages of the gasket 

 The structure types of metal tooth gaskets are basic type, with outer ring type, inner ring type and inner ring type. The more common structure is basic type. 

 Because the V-shaped bar in the surface contact area of the metal tooth gasket seal forms many space line contacts with differential pressure, the seal is reliable and has a long service life. Compared to ordinary metal gaskets, this kind of gasket requires less compressive force. 

 The disadvantage is that the two flange seals have to be processed every time the gasket is replaced, which is time-consuming and laborious. In addition, the gasket is easy to leave indentation on the flange seal surface after use, so it is generally used for less disassembly