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This post was copied from http://www.hzjg.net/bbs/redirect.php?tid=176742&goto=lastpost. I came across it by chance; I’m not sure if it’s original. Some of the content is quite basic, like the tenth item: Summary of Basic Knowledge on Flanges. 1. What is a loop flange, and where and in what types of piping components is it used? A swivel flange is a flange that can move; it is typically used in water supply and drainage fittings (most commonly on expansion joints). The manufacturer installs one flange at each end of the expansion joint, which are then connected to the pipes and equipment in the system using bolts. II. How are flanges connected to pipes? Where are they welded? There are many types of flanges. Generally, flat flanges, butt-welded flanges (long-neck flanges), slip-on flanges, etc. are used. Flat-face flanges are used for medium and low pressures; they are welded using the plug welding method, with welding on both sides, and the welding depth should be 2-5 mm from the flange’s sealing surface. Butt-face flanges can be welded directly, while slip-on flanges are connected using bolts without the need for welding. III. What does \"flange type\" mean? A flange is a connecting element used to link valves to pipes; when a valve is connected to a pipe, the connection is made using bolts. Therefore, if a valve has N evenly distributed bolt holes on its two end faces, it is of the flanged type. 1. Flange: Flange is the transliteration of “flange”; it refers to a component with a flange. Such a component can be standalone, in the form of a flange plate, or it can be part of a combined structure, such as when one or both ends of a pipe have flanges. These flanges have several holes for installing screws. Some bearing outer rings also have flanges, which may or may not have holes; they serve merely as edges for positioning purposes. 2. Flanged type: The connection between the valve and the pipeline or machinery equipment is achieved through flanges; this type of connection is therefore referred to as the flanged type. IV. What is a flange? A flange is a disc-shaped component that is most commonly used in piping systems, and flanges are always used in pairs. In pipeline engineering, flanges are mainly used for connecting pipelines. A flange is installed at each end of the pipe that needs to be connected; threaded flanges can be used for low-pressure pipes, while welded flanges are used for pipes under a pressure of 4 kilograms or more. A seal is added between the two flanges, which are then 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 thus 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 means it’s not appropriate to call the pump a \"flange-type component\". Smaller items such as valves can be referred to as \"flange components\". V. What kind of connection method is a flange? Flange connection is an important connection method in pipeline 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 pipe 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. 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 pipe fittings and equipment already come with flanges, and they also belong to the flange connection type. Be careful when making the connections, especially when tightening the bolts, to ensure that all bolts are tightened to the same degree. VI. What is the use of flanges? The flange is used for positioning. For example, one way of installing a cylinder is called flange mounting. In this method, four symmetric holes are drilled around a rectangular block; there is also a large hole in the center with the same diameter as that of the cylinder. This rectangular block is then fitted over the cylinder, and the two can be welded together or fixed in place using other methods. The connection between the cylinder and other components is achieved through these four holes around the rectangular block, and this rectangular block can thus be referred to as a flange. VII. How does the connection method of orifice plate flanges differ from that of ordinary flanges? It involves first fixing each of the two pipes, fittings, or components to a flange respectively; then placing a flange gasket between the two flanges and fastening them together with bolts to complete the connection. The orifice plate flange is used in orifice plate flowmeters to connect the orifice plate (the measuring element of the flowmeter) to the pipeline; the two flanges hold the orifice plate in place, and pressure taps on these flanges are used to transmit the pressure signal to a differential pressure transmitter, thereby enabling flow measurement. VIII. To ensure that the installed flanges do not leak oil, what issues should be taken into consideration during installation? 1. The flanges must have sufficient strength and must not deform when tightened. The flange sealing surface should be flat and clean; oil stains and rust spots must be thoroughly removed during installation. 2. The gasket should have good oil resistance and aging resistance, as well as decent elasticity and mechanical strength. During installation, gaskets of different cross-sections and sizes should be selected according to the shape of the joint, and placed correctly. 3. The tightening force of the flanges should be uniform, and the compression amount of the gasket should be kept at around 1/3. 9. What is the difference between butt-weld flanges and face-weld flanges? A butt weld flange has a pipe diameter and wall thickness at the joint that are identical to those of the pipes to be welded, allowing the two pipes to be welded together as if they were one. A flat weld flange features a recess at the joint that is slightly larger than the outer diameter of the pipe, with the pipe inserted into this recess and welded there. Butt welding has good weldability and suffers less corrosion. Flat welding and butt welding are the welding methods used for connecting flanges and pipes. With flat welding of flanges, welding is required only on one side; there is no need to weld the inner surfaces where the pipe and the flange meet. In contrast, butt welding of flanges requires welding on both sides of the flange. Therefore, socket weld flanges are generally used for low and medium pressure pipelines, while butt weld flanges are used for connecting medium and high pressure pipelines. Butt weld flanges usually have a pressure rating of at least PN2.5MPa; they are used to reduce stress concentration. Most butt weld flanges are necked flanges, also known as nipple flanges. Therefore, the installation cost for butt-weld flanges is higher, including labor and auxiliary materials costs, due to the additional processing step. Not all butt weld flanges require welding on both the inner and outer sides; in the absence of special requirements, welding is usually done only on the outside. Have you never seen a 1/2\" butt weld flange? :) Welding flanges in a flat position is easier, as it’s simpler to keep the pipe and the flange perpendicular to each other, preventing the pipe from being tilted. 10. What is the difference between flanges and valves? A valve is something like a faucet; in other words, a faucet is a type of valve. It can be unscrewed, and water or gas will flow out ； It can be closed, and the water will stop flowing. The water taps at home are screwed onto pipes using threads, but some of the pipes used in factories have very high pressures of water or gas inside; using threaded connections would not be secure enough, so they are welded together or connected using other methods. Flanges are one of such connection methods. XI. Flange Marking and Marking Examples 1. **Standard Marking: Flanges shall be marked with the nominal diameter, nominal pressure, code for the type of sealing surface, code for the series of steel pipe it is intended to be used with (the code for metric pipes is “Series 2”; no code is indicated for imperial pipes), and the standard number. Example of markings: Raised face butt-welded steel pipe flange with a nominal diameter of 80 mm and a nominal pressure of 4.0 MPa (25 bar) (for metric pipes); Flange DN80－PN40 M (Series 2), GB/T9115.2－2000. Raised face wafer-type butt-welded steel pipe flange with a nominal diameter of 100 mm and a nominal pressure of 5.0 MPa (25 bar) (for imperial pipes); Flange DN100－PN50 RF, GB/T9116.1－2000. 2. Marking according to Ministry of Machinery standards: Example of marking: Raised face butt-welded steel pipe flange, nominal diameter 500 mm, nominal pressure 1.6 MPa, Series 2 – Flange 500‑16 JB/T81‑94; Concave face butt-welded steel pipe flange, nominal diameter 300 mm, nominal pressure 6.4 MPa, Series 1 – Flange 300‑64B (Series 1) JB/T82.2‑94. (Note: According to Ministry of Machinery standards, the outer diameter of the pipe is assumed to be that of Series 2; for butt-welded flanges, the classifications are Type A for raised face, Type B for concave face, Type C for tenon face, and Type D for groove face.) 3. Marking according to Ministry of Chemical Industry standards: Flanges shall be marked in accordance with the following regulations (this marking method is recommended): a. Standard number: All types of pipe flanges are uniformly marked with the standard number of this standard: HG20592. b. The flange type code shall be in accordance with the provisions of Table 5.0.1. When tapered pipe threads specified in GB/T7306 are used for threaded flanges, they are marked as “Th(Rc)” or “Th(Rp)”” ； When a threaded flange uses tapered pipe threads as specified in GB/T12716, it is marked as “Th(NPT)”” ； If a threaded flange is not marked with a thread code, it is Rp (GB/T7306.1). c. Nominal flange diameter DN (mm) and applicable outer diameter series of steel pipes: integral flanges, flange covers, lined flange covers, threaded flanges; the designation of the applicable outer diameter series of steel pipes may be omitted ； Flanges suitable for the internationally standard series of steel pipes (commonly known as imperial pipes), marked “DN(A)”” ； Flanges suitable for domestic standard series steel pipes (commonly known as metric pipes) are marked as “DN(B)”. d. Nominal flange pressure PN, MPa. e. The code for the type of sealing surface shall be in accordance with the provisions of Table 6.0.1; for raised-face flanges with machined serrated grooves, it shall be marked as “RF (A)”. f. The wall thickness of the steel pipe to be provided by the user. For flanges with necks and welded flanges, as well as loose-flange welded rings, the wall thickness of the steel pipe shall be indicated. g. Material grade. h. Others. Requirements or additional requirements that are not consistent with those specified in this standard series, such as the surface roughness of the sealing surfaces, may be adopted. Example of markings: Nominal diameter 1200 mm, nominal pressure 0.6 MPa; raised face flat welding steel pipe flange for metric pipes, material Q235A, standard HG20592, flange type PL1200(B) – 0.6 RF, material Q235A. Nominal diameter 300 mm, nominal pressure 2.5 MPa; raised face welded neck flat welding steel pipe flange for imperial pipes, material 20 steel, standard HG20592, flange type SO300(A) – 2.5 M, material 20. Nominal diameter 150 mm, nominal pressure 16.0 MPa; ring joint face welded neck butt welding steel pipe flange for imperial pipes, material 16Mn, pipe wall thickness 10 mm, standard HG20592, flange type WN150(A) – 16.0 RJ, S = 10 mm, material 16Mn. Nominal diameter 200 mm, nominal pressure 1.0 MPa; raised face welded ring loose sleeve steel pipe flange for metric pipes, materials: flange 20, welded ring 316, pipe wall thickness 4 mm, standard HG20592, flange type PJ/SE200(B) – 1.0 RF, S = 4 mm, materials 20/316. Last edited by Pseudo Xiaobao on 2009-3-3 23:34.]