Comprehensive guide to 12 types of flanges and sealing surface configurations

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Do you know everything about the 12 types of flanges and sealing surface configurations? Pipe and valve internal parameters. Pipe and valve internal parameters – yesterday: basic introduction. Pipe flanges, along with their gaskets and fasteners, are collectively referred to as flanged joints. Applications: Flange joints are a type of component that is extremely common and widely used in engineering design. It is an essential component for piping design, as well as for fittings and valves; it is also a necessary part of equipment and its components (such as manholes, sight glasses, level gauges, etc.). In addition, other specialties such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, and automatic control also frequently use flange joints. Materials: forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chromium-molybdenum steel, chromium-molybdenum-vanadium steel, molybdenum-dititanium, rubber-lined, fluorine-lined materials. Categories: flat welding flanges, necked flanges, butt welding flanges, ring-connected flanges, socket weld flanges, and blind flanges, etc. Execution standards: There are GB series (**standard), JB series (Ministry of Machinery), HG series (Ministry of Chemical Industry), ASME B16.5 (American standard), BS4504 (British standard), DIN (German standard), and JIS (Japanese standard). International pipe flange standard systems: Internationally, there are mainly two systems of pipe flange standards – the European system represented by German DIN (including the former Soviet Union) and the American system represented by ANSI pipe flanges. Type and seal surface configuration: 1. Plate-type face weld flange. Plate-type face weld flange (chemical industry standard HG20592, **standard GB/T9119, mechanical standard JB/T81). Advantages: Easy to obtain materials, simple to manufacture, low cost, and widely used. Disadvantages: Poor rigidity; therefore, it cannot be used in chemical process piping systems that require resistance to pressure fluctuations, as well as in environments with high fire and explosion risks or extreme vacuum conditions. The seal surface types include flat and convex surfaces. 2. Welding flange with neck: Welding flanges with neck fall under the national standard flange classification system. It is one form of national standard flanges (also known as GB flanges), and it is one of the commonly used flanges on equipment or pipelines. Advantages: It is convenient for on-site installation, and the process of damaging the welds due to handling can be omitted. Disadvantages: The neck height of flanges with a necked design is relatively low, which reduces the stiffness and load-bearing capacity of the flanges. Compared to butt-welded flanges, they require more welding work and consume more welding electrodes; they cannot withstand high temperatures and pressures, as well as repeated bending and temperature fluctuations. 3. Welded flanges with necks. The seal surface types for welded flanges with necks include: raised face (RF), recessed face (FM), male face (M), female face (T), grooved face (G), and full flat face (FF). Advantages: The connection is not prone to deformation, it provides good sealing performance, and it has a wide range of applications. It is suitable for pipes subject to large fluctuations in temperature or pressure, as well as for pipes operating under high, low, or extreme temperatures. It is also used in pipes that transport expensive media, flammable and explosive substances, and toxic gases. Disadvantages: Wafer-type butt weld flanges are large in size, heavy in weight, expensive, and difficult to install and position. Therefore, it is more prone to damage during transportation. 4. Integral flange: An integral flange is a type of flange connection method. It also belongs to the category of steel pipe flanges with necks for butt welding. Materials include carbon steel, stainless steel, alloy steel, etc. Among various domestic standards, IF is used to denote the overall flange. It is commonly used in pipes under high pressure. The manufacturing process is generally casting. In the flange type, an “IF” is used to represent the overall flange type. It is generally a raised face (RF); however, in applications where there is a risk of fire, explosion, or high/extreme hazards, sealing surfaces other than RF faces, such as male-female faces (MFM) and tongue-and-groove faces (TG), can be used. 5. Socket weld flange: A socket weld flange is a flange whose one end is welded to the steel pipe while the other end is connected using bolts. Seal surface types: Raised face (RF), Male and female face (MFM), Tongue and groove face (TG), Ring joint face (RJ). Applications: Boiler and pressure vessels, petroleum, chemical industry, shipbuilding, pharmaceuticals, metallurgy, machinery, stamping elbows, food industry, and other sectors. It is commonly used in pipelines with PN≤10.0MPa and DN≤40. 6. Threaded flanges: Threaded flanges are those in which the inner hole of the flange is processed into pipe threads, allowing them to be connected to threaded pipes; they represent a type of non-welded flange (WeChat official account: Pump Manager). Advantages: Compared to slip-on flanges or butt-welded flanges, threaded flanges are easier to install and maintain, and can be used on pipelines where welding is not permitted. Alloy steel flanges have sufficient strength, but are difficult to weld or have poor weldability; threaded flanges can also be an option. Disadvantage: In situations where the pipe temperature changes rapidly, or when the temperature is above 260°C or below -45°C, it is recommended not to use threaded flanges to avoid leaks. 7. Welded ring loose-flange: A welded ring loose-flange is a type of flange that can move; it is generally used in water supply and drainage fittings. The manufacturer installs a flange at each end of the expansion joint, which are then connected directly to the pipes and equipment in the system using bolts. Function: The purpose of using butt-welded ring loose-flange connections is generally to save material. Its structure consists of two parts: one end of the pipe section is connected to the pipeline, while the other end is designed as a butt-welding ring. The flanges are made of lower-grade materials, while the pipe sections use the same material as the pipelines, in order to save materials. Advantages: Cost savings. When the pipe material is special and expensive, welding flanges of the same material is costly as well. It is not suitable for welding or processing, or it requires high strength. Such as plastic pipes, fiberglass pipes, and the like. Facilitates construction. For example, when connecting, it may be difficult to align the flange bolt holes, or there might be changes in those holes later on when the equipment is replaced. Disadvantage: Low stress tolerance. Low strength at the weld ring (especially when the thickness is below 3 mm). 8. Slip-on flanges with flat weld rings: Slip-on flanges with flat weld rings are flange plates that can move. It is directly bolted to the pipes and equipment in the plant. The purpose of using slip-on flanges with flat welding rings is generally to save material. Its structure consists of two parts: one end of the pipe is connected to the pipeline, while that end is formed into a flange; the flange part is then fitted over this flange. Advantages: Easy to weld or process, or requires high strength, such as plastic pipes, fiberglass pipes, etc. It facilitates construction, such as by ensuring that the flange bolt holes align properly during connection, or preventing any changes in those bolt holes when the equipment is replaced in the future. When prices are high, save on costs. When the pipe material is special, welding flanges of the same material is costly. Disadvantage: Low tolerance for stress. Low strength at the weld ring (especially when the thickness is 3 mm or less). 9. Flange cover, also known as blind flange or plug flange. It is a flange without holes in the middle, used to seal pipe plugs. Its function is the same as that of welded end caps and threaded pipe caps, except that blind flanges and threaded pipe caps can be removed at any time, while welded end caps cannot. Flange cover sealing surfaces: Flat (FF), Raised (RF), Male and Female (MFM), Tongue and Groove (TG), Ring Joint (RJ). 10. Lined flange cover: A lined flange cover is a type of blind flange; stainless steel is welded on the side in contact with the medium, forming a single unit. Lined flange covers are used as blind plates on pipes containing corrosive media. The difference from ordinary flange covers is that an anti-corrosion lining has been added to the surface in contact with the medium. 11. American standard wafer flanges with necks – Wafer flanges with necks are used to connect pipe ends. They are mainly the parts that connect pipes to each other. The butt-weld flange with a neck has holes through which bolts can be passed to tightly connect the two flanges, with gaskets used for sealing between them. 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 connection. Based on the connected components, they can be divided into container flanges and pipe flanges. Flat welding flanges with necks are suitable for connecting steel pipes with a nominal pressure not exceeding 2.5 MPa. The necked flat welding flange is used for the butt welding of flanges and pipes. It features a rational design, high strength and stiffness, and can withstand high temperatures and pressures as well as repeated bending and temperature fluctuations, offering reliable sealing performance. Flat-welded flanges with necks having a nominal pressure of 0.25–2.5 MPa feature male and female sealing surfaces. 12. American standard butt-weld flanges. American standard flanges are components used to connect pipes to each other, and they are attached to the ends of pipes. American standard butt weld flanges are manufactured by two methods: forging and casting. According to whether they have a neck, ANSI weld flanges can be divided into ANSI weld flanges with a neck and ANSI weld flanges without a neck. A US standard butt weld flange is formed by two flange discs along with a flange gasket, which are fastened together with bolts to complete the connection. American standard flanges have holes, and bolts are used to fasten the two flanges together. The flanges are sealed with gaskets.