Flange sealing surface issues

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Table of flange sealing surface types: Name, Features, Description, Schematic. Raised face (RF): The surface is a smooth plane; it can also be machined with fine grooves. The sealing surface has a simple structure, is easy to machine, and facilitates the application of anti-corrosion linings. However, this type of sealing face gasket has a large contact area, and it tends to be pushed to the sides during pre-tightening, making it difficult to compress tightly. (Figure a) The MFM sealing surface is composed of a convex surface and a concave surface; a gasket is placed on the concave surface to prevent it from being pushed out, making it suitable for applications with high pressures. (Figure b) The tenon-groove surface (TG) sealing surface is composed of a tenon and a groove; the gasket is placed in the groove and will not be displaced. The gasket can be narrower, so the bolt force required to compress it is correspondingly smaller. Even in areas with high pressure, the bolt size does not have to be excessively large. Therefore, it achieves a better sealing effect than both of the aforementioned sealing surfaces. The disadvantage of the sealing surface is that its structure and manufacturing are relatively complex, and it is difficult to replace the gasket packed in the groove. Furthermore, the tenon surface is prone to damage, so care should be taken during disassembly, assembly, or transportation. The tenon-and-socket sealing surface is suitable for flammable, explosive, toxic media as well as applications with high pressures. When the pressure is low, it can achieve good sealing even with a larger diameter. (Figure (c)) Full-flat (FF) and ring joint face (RJ) full-flat sealing is suitable for applications with low pressure (PN≤1.6MPa) ； The ring joint face is mainly used on necked butt-weld flanges and integral flanges, with a pressure range of (6.3 MPa ≤ PN ≤ 25.0 MPa). (Figures (d) and (e)) Other types of sealing surfaces: For the sealing of high-pressure vessels and high-pressure pipes, conical sealing surfaces or trapezoidal groove sealing surfaces can be used; these work in conjunction with spherical metal gaskets (lens gaskets) as well as metal gaskets with an oval or octagonal cross-section. Sealing surfaces can be used in applications with high pressure, but they require high dimensional accuracy and surface finish, making them difficult to manufacture. (Figure 4-37) (Figure 4-38) Appendix 1: Appendix 1: Appendix 1: Appendix 1: Flange sealing diagram; Flange types and seal surface configurations; Flange standard numbers; Seal surface pressure ratings: PN, in MPa. Common flange type codes for valves: Plate type, flat welding PLHG20593, JB/T81-94, GB/T9119-2000; Raised face RF, 0.25–2.5. Raised face flat welding flanges are commonly used and can be paired with various low- and medium-pressure valve types such as gate valves, globe valves, ball valves, etc. Full flat face FF, 0.25–1.6; Necked type, flat welding SOHG20594, GB/T9116-2000; Raised face RF, 0.6–4.0. Raised face necked flat welding flanges are a structure commonly used in petrochemical plants in recent years. Grooved face MFM, 1.0–4.0; Tenon groove face TG, 1.0–4.0; Full flat face FF, 0.6–1.6; Necked type, butt welding WNHG20595, JB/T82-94, GH/T9115-2000. Valves with PN 4.0–PN10.0 MPa usually use raised face pipe flanges, such as Z41H-40, J41H-64, H44H-100, etc. For pressures above 160, ring joint faces are used, such as J41H-160. Butt welding flanges can also be used with butterfly valves and check valves that employ clamp-type connections. Rough-faced MFM 1.0–16.0, tenon-faced TG 1.0–16.0, ring-connected RJ 6.3–25.0, fully flat FF 1.0–1.6; integral flange IFHG20596, JB/T79-94, GB/T9113-2000. Rough-faced RF 0.6–25.0: For valves, integral flanges are generally used with a rough surface for PN≤2.5, a rough surface for PN≥4.0, and a ring-connected design for PN≥16.0; however, some manufacturers use a ring-connected design for PN10.0 MPa and a rough surface for PN16.0 MPa. Note that ammonia valves with PN2.5 MPa use a rough surface (FM) and require pipe flanges with a rough surface. Rough-faced MFM 1.0–16.0, tenon-faced TG 1.0–16.0, ring-connected RJ 0.6–25.0, fully flat FF 1.0–1.6; socket-welded SWHG20597, GB/T9114-2000. Rough-faced RF 1.0–10.0: This is a structural design commonly used in petroleum processing units introduced in recent years. The ribbed surface MFM1.0～10.0, the tenon groove surface TG1.0～10.0, threads, and flanges ThHG20598 and GB/T9114-2000 are commonly used in engineering construction; they are easy to install without the need for welding, and are suitable for DN10-DN150 sizes. The raised surface RF0.6～4.0 is also frequently utilized in such applications. Full-flat FF0.6～1.6 butt-welded ring loose sleeve PJ/SEHG20599, JB/T84-94, GB/T9120-2000; raised face RF0.6～4.0 – suitable for pipeline systems exposed to corrosive media. Sewel welding: Ring loose sleeve PJ/RJHG20600, JB/T83-94, GB/T9121-2000; convex surface RF0.6～1.6, uneven surface MFM1.0～1.6, tenon groove surface TG1.0～1.6; flange cover BLHG20601, JB/T84-94, GB/T9123-2000; convex surface RF0.25～25.0 – used for pipe ends or as end caps. Ribbed surface: MFM 1.0–16.0; Socketed surface: TG 1.0–16.0; Ring joint surface: RJ 6.3–25.0; Fully flat surface: FF 0.25–1.6. For American standard valves with a neck, use socket weld connection SOHG20616; for those with a raised surface, use RF 2.0–26.0. Pressure ratings range from PN2.5 to PN5.0. For American standard valves with a neck, use butt weld connection WNHG20617; for those with a raised surface, use RF 2.0–42.0. Generally, raised surfaces are used when the pressure rating is ≤11.0 MPa, while ring joint surfaces are used when the pressure rating is ≥15.0 MPa. Selection of flange seal face type: Full flat seal face: Often used in combination with the butt-welded type to suit operating conditions that are relatively mild (PNg1.0) ； Commonly used for cast iron flanges or steel flanges connected to cast iron ； Raised face seal surface: This is the most widely used type; it is often used in combination with butt welding and socket welding methods. In \"American flanges\", it is commonly employed for pressure ratings of PN2.0, PN5.0, and some PN10.0 MPa grades ； In \"European flanges\", it is commonly used for pressure grades of PN1.6 and PN2.5 MPa ； Rough and smooth sealing surfaces: Often used in combination with butt-welding and socket-type connections; not commonly used in American flanges, but are frequently employed in European flanges for PN4.0 and PN6.4 MPa pressure classes. But it is not convenient for replacing the gasket ； Tenon-and-socket surface sealing surface: The same application as male-and-female flanges ； Ring groove face seal surface: It is commonly used in conjunction with butt welding connections (not with socket welding), and is primarily applied in conditions of high temperature, high pressure, or both. In \"American flanges\", they are commonly used in pressure classes of PN10.0 (in some cases), PN15.0, PN25.0, and PN42.0 MPa. In \"European flanges\", PN10.0, PN16.0, PN25.0, PN32.0, and PN4200 are commonly used. 1. Flange connection: The flange connection is an important method of piping construction. Flange connection involves first fixing two pipes, fittings, or components to separate flanges, placing a flange gasket between the two flanges, and then fastening them together with bolts to complete the connection. Some fittings and equipment already come with flanges, and they also belong to the flange connection type. Flanges are divided into threaded flanges and welded flanges. For low-pressure applications with small diameter threaded flanges, welded flanges are used for high-pressure and low-pressure applications with large diameter flanges. The thickness of the flanges, as well as the diameter and quantity of the connecting bolts, vary depending on the pressure level. Depending on the different pressure levels, flange gaskets are made from various materials, ranging from low-pressure asbestos gaskets and high-pressure asbestos gaskets to metal gaskets. Flange connections are easy to use and can withstand high pressures. Flange connections are widely used in industrial pipelines. Within the household, the pipe diameter is small and the pressure is low; flange connections are not visible. In a boiler room or production facility, there are pipes and equipment connected by flanges everywhere. It is also called a flange or rim. Parts that connect pipes to each other. Connected to the pipe end. The flanges have holes through which bolts can be passed to tightly connect the two flanges. The flanges are sealed with gaskets. Flanged pipe fittings refer to pipe fittings that have flanges (ridges or plates). It can be formed by casting (figure not available), or it can be constructed through threaded connection or welding. A flange joint consists of a pair of flanges, a gasket, and several bolts and nuts. The gasket is placed between the sealing surfaces of the two flanges; once the nuts are tightened, the compressive stress on the surface of the gasket reaches a certain level, causing it to deform and fill in any unevenities on the sealing surfaces, thereby ensuring a tight seal with no leaks. Flange connection is a detachable type of connection. Based on the connected components, they can be divided into container flanges and pipe flanges. Classified by structure type, there are integral flanges, slip-on flanges, and threaded flanges. Common integral flanges include flat welding flanges and butt welding flanges. Flat-weld flanges have poor rigidity and are suitable for applications with a pressure of p≤4MPa ； Butt weld flanges, also known as high-neck flanges, have high rigidity and are suitable for applications with high pressure and temperature. There are three types of flange sealing surfaces: the flat-type sealing surface, which is suitable for applications with low pressure and non-toxic media ； Roughened sealing surface, suitable for applications with slightly higher pressure ； Tenon-and-socket sealing surface, suitable for flammable, explosive, toxic media and high-pressure applications. A gasket is a ring made of a material that can undergo plastic deformation and possesses certain strength. Most gaskets are cut from non-metallic sheets, or manufactured by specialized factories to specified dimensions; their materials include asbestos rubber sheets, asbestos sheets, polyethylene sheets, etc ； There are also metal gasket inserts made by wrapping non-metallic materials such as asbestos with thin metal sheets (galvanized steel, stainless steel) ； There is also a type of wound gasket made by winding thin steel strips together with asbestos strips. Ordinary rubber gaskets are suitable for applications with temperatures below 120°C ； Asbestos rubber gaskets are suitable for applications where the temperature of water vapor is below 450°C, the temperature of oils is below 350°C, and the pressure is below 5 MPa. For general corrosive media, acid-resistant asbestos sheets are the most commonly used. In high-pressure equipment and pipelines, lens-shaped or other shaped metal gaskets made of copper, aluminum, grade 10 steel, and stainless steel are used. The contact width between the high-pressure gasket and the sealing surface is very narrow (linear contact), and both the sealing surface and the gasket have a high level of surface finish. 2. Flange: Flam, now known as “Phalam”. A city in western Myanmar, the capital of Chin State. To the east it borders the Manipur River, a tributary on the right bank of the Chindun River; to the west it is adjacent to Ram Kalan Mountain. There are roads leading east to Mandalay, north into India to Imphal, and south via the newly built Haka-Gango road to various parts of southern Myanmar. A flange is a disc-shaped component that is most commonly used in piping projects, and flanges are always used in pairs. In piping engineering, flanges are mainly used for connecting pipes. A flange is installed at each end of the pipeline that needs to be connected; threaded flanges can be used for low-pressure pipelines, while welded flanges are used for pipelines with pressures above 4 kilograms. A seal is added between the two flanges, and then they are tightened with bolts. Flanges under different pressures have different thicknesses and require different bolts. When water pumps and valves are connected to pipes, the corresponding parts of these devices are also made in the shape of flanges, a connection method known as flange coupling. Any connecting component that uses bolts to join two planes together at their perimeters and thereby seals them is generally referred to as a \"flange\"; for example, in the connection of ventilation ducts, such components can be called \"flange-type components\". However, such a connection is only a local part of a device; for example, the connection between a flange and a pump doesn’t allow the pump to be called a \"flange-type component\". Smaller items such as valves can be referred to as \"flange components\".