First, a basic introduction to flanges
Pipe flanges and their gaskets and fasteners are collectively referred to as flange joints.
1. Application: Flange joints are a very common and widely used component in engineering design. It is an indispensable part of piping design, pipe fittings, and valves, and it is also a necessary component in equipment and equipment parts (such as manholes, sight glass liquid level gauges, etc.). In addition, other professions such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, automatic control, etc., also often use flange joints.
2. Material: forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chrome-molybdenum steel, chrome-molybdenum-vanadium steel, molybdenum-titanium, rubber lining, fluorine lining material.
3. Classification: flat welding flange, neck flange, butt welding flange, ring connection flange, socket flange, blind plate, etc.
4. Implementation standards: GB series (national standard), JB series (Ministry of Machinery), HG series (Ministry of Chemical Industry), ASME B16.5 (American standard), BS4504 (British standard), DIN (German standard), JIS (Japanese standard).
5. International pipe flange standard system:
There are two main systems of pipe flange standards internationally.
The European pipe flange system represented by German DIN (including the former Soviet Union)
The American pipe flange system is represented by the American ANSI pipe flange.
Second, 12 types of flanges and their characteristics
1. Plate flat welding flange: Plate flat welding flange (chemical standard HG20592, national standard GB/T9119, mechanical JB/T81).
Advantages: convenient material acquisition, simple manufacturing, low cost, and wide use.
Disadvantages: poor rigidity, so it should not be used in chemical process piping systems with supply and demand, flammable, explosive, and high vacuum requirements, and high and extremely hazardous occasions. The sealing surface types are flat and raised.
2. Necked flat welding flange: Necked flat welding flange belongs to the national standard flange standard system, is one of the manifestations of national standard flange (also known as GB flange), and is one of the commonly used flanges on equipment or pipelines.
Advantages: It is convenient to install on-site, and the process of patting and rubbing the weld can be omitted.
Disadvantages: The neck height of the necked flat welding flange is relatively low, which improves the rigidity and bearing capacity of the flange. Compared with the butt welding flange, the welding workload is large, the welding rod consumption is high, and it cannot withstand high temperature and high pressure, repeated bending, and temperature fluctuations.
3. Necked butt welding flange: The sealing surface forms of the necked butt welding flange are: raised face (RF), concave face (FM), convex face (M), tenon face (T), groove face (G), full plane (FF).
Advantages: The connection is not easy to deform, the sealing effect is good, and it is widely used. It is suitable for pipelines with large fluctuations in temperature or pressure or pipelines with high temperature, high pressure, and low temperature. It is also used for pipelines that transport expensive media, flammable and explosive media, and toxic gases.
Disadvantages: Neck butt welding flanges are large in size, heavy, expensive, and difficult to install and position, so they are more likely to bump during transportation.
4. Integral flange: Integral flange is a flange connection method. It is also a type of neck butt welding steel pipe flange. The materials include carbon steel, stainless steel, alloy steel, etc. In various domestic standards, IF is used to represent integral flanges. It is mostly used in pipelines with higher pressure, and the production process is generally casting. In the flange type, an “IF” is used to represent the type of integral flange. Generally, it is a raised face (RF). If it is used in flammable, explosive, high, and extremely hazardous working conditions, you can choose the sealing surface of the convex and concave surface (MFM) and the tongue and groove surface (TG) in addition to the RF surface.
5. Socket welding flange: The socket welding flange is a flange that is welded to the steel pipe at one end and bolted at the other end.
Sealing surface form: raised face (RF), concave and convex surface (MFM), tongue and groove surface (TG), ring joint surface (RJ).
Application range: boiler pressure vessels, petroleum, chemical, shipbuilding, pharmaceutical, metallurgy, machinery, food and other industries. Commonly used in pipelines with PN≤10.0MPa, DN≤40.
6. Threaded flange: The threaded flange is a non-welded flange that processes the inner hole of the flange into a pipe thread and connects it with a threaded steel pipe.
Advantages: Compared with flat welding flanges or butt welding flanges, threaded flanges are easy to install and maintain, and can be used on pipelines where welding is not allowed on site. Alloy steel flanges have sufficient strength, but are not easy to weld, or have poor welding performance, and threaded flanges can also be selected.
Disadvantages: Under conditions where the pipeline temperature changes sharply or the temperature is higher than 260℃ and lower than -45℃, it is recommended not to use threaded flanges to avoid leakage.
7. Butt welding ring loose flange: Butt welding ring loose flange is a movable flange, which is generally equipped with water supply and drainage accessories. When the manufacturer leaves the factory, there is a flange at each end of the expansion joint, which is directly connected to the pipelines and equipment in the project with bolts.
Function: The purpose of using a butt-welded ring loose flange is generally to save materials. Its structure is divided into two parts. One end of the steel pipe part is connected to the pipeline, and the other end is made into a butt-welded ring. The flange is made of low-grade materials, while the steel pipe part uses the same material as the pipeline to achieve the purpose of saving materials.
Advantages: Save costs. When the pipe material is special and expensive, the cost of welding flanges of the same material is high. It is not convenient to weld or process or requires high strength, such as plastic pipes, fiberglass pipes, etc. It is convenient for construction, such as when the flange bolt holes are connected, it is not convenient to align or prevent the flange bolt holes from changing when replacing equipment in the future.
Disadvantages: Low-pressure resistance and low strength at the welding ring (especially when the thickness is less than 3mm).
8. Flat welding ring loose flange: A flat welding ring loose flange is a movable flange that is directly connected to the pipeline and equipment in the project with bolts. The purpose of using a flat welding ring loose flange is generally to save materials. Its structure is divided into two parts. One end of the steel pipe is connected to the pipeline, and the other end is made into a flange, and the flange part is sleeved on the flange.
Advantages: Convenience for welding or processing or high strength is required, such as plastic pipes, fiberglass pipes, etc. Convenient for construction, such as the flange bolt holes corresponding to each other during connection is convenient for alignment or preventing the flange bolt holes from changing when replacing equipment in the future. Save costs when the price is expensive. When the pipe material is special, the cost of welding flanges of the same material is high.
Disadvantages: Low-pressure acceptance. Low strength at the welding ring (especially when the thickness is less than 3mm).
9. Flange cover: also known as blind flange, blind plate, is a flange without a hole in the middle, used to seal the pipe plug. The function is the same as that of the welding head and threaded pipe cap, except that the blind flange and threaded pipe cap can be removed at any time, while the welding head cannot.
Flange cover sealing surface: flat surface (FF), raised surface (RF), concave and convex surface (MFM), tongue and groove surface (TG), ring connection surface (RJ)
10. Lined flange cover: Lined flange cover is a blind flange, and the side close to the medium is welded with stainless steel as a whole. A lined flange cover is used as a blind plate on pipelines with corrosive media. The difference from an ordinary flange cover is that an anti-corrosion lining is added to the contact surface with the medium.
11. American standard flat-weld flange with neck: The flat-weld flange with neck is connected to the pipe end, and it is mainly a part that connects steel pipes. There are holes on the flat-weld flange with the neck, which can be penetrated by bolts to make the two flanges tightly connected, and the flanges are sealed with gaskets. The gasket is placed between the sealing surfaces of the two flanges. After tightening the nut, the gasket surface deforms after the specific pressure reaches a certain value, and fills the uneven parts on the sealing surface, making the connection tight and leak-proof. A flange connection is a detachable connection, which can be divided into a container flange and a pipe flange according to the connected parts. Neck flat-weld flange is suitable for steel pipeline connection with a nominal pressure not exceeding 2.5MPa. Neck flat-weld flange is used for butt welding of flange and steel pipe. It has a reasonable structure, high strength and rigidity, can withstand high temperature and high pressure, repeated bending and temperature fluctuations, and reliable sealing. The flat welding flange with a neck with a nominal pressure of 0.25 to 2.5 MPa adopts a concave and convex sealing surface.
12. American standard butt welding flange with a neck: The American standard flange is a part that connects steel pipes and is connected to the pipe end. The American standard butt welding flange is made by forging and casting. The American standard butt welding flange can be divided into an American standard butt welding flange with a neck and an American standard butt welding flange without a neck according to the neck situation. The American standard butt welding flange consists of two flange plates plus a flange gasket, which are fastened together with bolts to complete the connection. There are holes on the American standard flange, and the bolts make the two flanges tightly connected, and the flanges are sealed with gaskets.
Post time: Oct-15-2024