Basic Introduction to Flanges
Pipe flanges, along with their gaskets and fasteners, are collectively referred to as flange joints.
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1. Applications:
Flange joints are a widely used and essential component in engineering design. They are indispensable parts in piping design, pipe fittings, and valves, and are also essential components in equipment and equipment parts (such as manholes, sight glasses, and liquid level gauges). Furthermore, flange joints are frequently used in other disciplines such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, and automation.
2. Materials:
Forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chrome-molybdenum steel, chrome-molybdenum-vanadium steel, molybdenum-titanium steel, rubber-lined, and fluoropolymer-lined materials.
3. Classifications:
Slip-on flanges, neck flanges, butt-welding flanges, ring flanges, socket flanges, and blind flanges, etc.
4. Standards Applied:
Includes GB series (National Standard), JB series (Ministry of Machinery Industry), HG series (Ministry of Chemical Industry), ASME B16.5 (American Standard), BS4504 (British Standard), DIN (German Standard), and JIS (Japanese Standard).
5. International Pipe Flange Standard System:
Internationally, there are two main pipe flange standard systems:
The European pipe flange system, represented by German DIN (including the former Soviet Union).
The American pipe flange system, represented by American ANSI pipe flanges.
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12 Flange Types and Characteristics
1. Plate-Type Slip-On Flange
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Plate-type slip-on flange (Chemical Standard HG20592, National Standard GB/T9119, Machinery Standard JB/T81).
Advantages:
Easy to source materials, simple to manufacture, low cost, and widely used.
Disadvantages:
Poor rigidity; therefore, it cannot be used in chemical process piping systems with supply and demand requirements, flammable, explosive, or high vacuum requirements, or in highly hazardous or extremely dangerous environments. 1. Sealing face types include flat face and raised face.
2. Necked Welding Flange
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Necked welding flanges belong to the national standard flange system and are one of the manifestations of national standard flanges (also known as GB flanges). They are one of the commonly used flanges on equipment or pipelines.
Advantages:
Easier to install on site, eliminating the need for weld seam patting.
Disadvantages:
The neck height of necked welding flanges is lower, which increases the flange's rigidity and load-bearing capacity. Compared with welding flanges, the welding workload is larger, welding rod consumption is higher, and they cannot withstand high temperature and pressure, repeated bending, and temperature fluctuations.
3. Necked Welding Flange
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The sealing face types of necked welding flanges include:
Raised face (RF), concave face (FM), raised face (M), tongue and groove (T), grooved face (G), and flat face (FF).
Advantages:
The connection is not easily deformed, has good sealing effect, and is widely used. It is suitable for pipelines with large temperature or pressure fluctuations, or for high-temperature, high-pressure, and low-temperature pipelines. It is also used in pipelines transporting expensive media, flammable and explosive media, and toxic gases.
Disadvantages:
Weld neck flanges are bulky, heavy, expensive, and difficult to install and position, making them more susceptible to damage during transportation.
4. Integral Flange
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An integral flange is a type of flange connection. It is also a type of weld neck steel pipe flange. Materials include carbon steel, stainless steel, and alloy steel.
In various domestic standards, integral flanges are represented by "IF". They are mostly used in high-pressure pipelines, and the manufacturing process is generally casting.
In flange types, "IF" is used to indicate the type of integral flange. It is generally a raised face (RF). In flammable, explosive, highly hazardous, and extremely hazardous operating conditions, other sealing face types such as faceless (MFM) and tongue and groove (TG) can be selected.
5. Socket Welding Flange
[Image] [Image] A socket welding flange is a flange where one end is welded to a steel pipe and the other end is bolted.
Sealing Face Types:
Raised Face (RF), Dysfunction Face (MFM), Tongue and Groove (TG), Ring Joint (RJ).
Applications:
Boiler pressure vessels, petroleum, chemical, shipbuilding, pharmaceutical, metallurgy, machinery, food, and other industries.
Commonly used in pipelines with PN≤10.0MPa and DN≤40.
6. Threaded Flange
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A threaded flange is a non-welded flange where the inner bore is machined with pipe threads and connected to a threaded pipe.
Advantages:
Compared to flat-welded or weld neck flanges, threaded flanges are easier to install and maintain, and can be used on pipelines where welding is not permitted on-site. Alloy steel flanges have sufficient strength but are difficult to weld or have poor weldability; threaded flanges can also be chosen in such cases.
Disadvantages:
Threaded flanges are not recommended for use under conditions of rapid pipe temperature changes or temperatures above 260℃ and below -45℃ to prevent leakage.
7. Weld-on-Ring Loose Flange
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Weld-on-ring loose flanges are movable flanges, typically used with water supply and drainage fittings. Manufacturers usually ship expansion joints with one flange at each end, directly bolted to the pipes and equipment in the project.
Function:
The purpose of using weld-on-ring loose flanges is generally to save materials. Their structure consists of two parts: one end connects to the pipe, and the other end is formed by a weld-on ring. The flange uses a lower-grade material, while the pipe part uses the same material as the pipe, achieving material savings.
Advantages:
Cost-saving: When the pipe material is special and expensive, welding a flange of the same material is costly. Not suitable for welding, processing, or applications requiring high strength, such as plastic pipes or fiberglass pipes. Facilitates construction: For example, it can be helpful if the flange bolt holes are not aligned correctly during connection or if changes in bolt hole alignment are needed when replacing equipment later. Disadvantages:
Low pressure resistance; low strength at the weld ring (especially when the thickness is less than 3mm).
8. Flat-face weld ring loose flange
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A flat-face weld ring loose flange is a movable flange that is directly bolted to pipes and equipment in an engineering project.
The purpose of using a flat-face weld ring loose flange is generally to save materials. Its structure is divided into two parts: one end of the pipe is connected to the pipe, and the other end is made into a flange, with the flange fitting over the flange.
Advantages:
Easy to weld, easy to process, or suitable for applications requiring high strength, such as plastic pipes and fiberglass pipes.
Easy to construct, such as facilitating alignment of flange bolt holes during connection or preventing changes in flange bolt holes when replacing equipment later.
Saving costs when the price is high. However, when the pipe material is special, welding a flange of the same material is costly.
Disadvantages:
Low pressure resistance.
Low strength at the weld ring (especially when the thickness is less than 3mm).
9. Flange Cover
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Also known as a blind flange or blind plate, it is a flange without a central hole, used to seal pipe ends. Its function is the same as welded caps and threaded caps, except that blind flanges and threaded caps can be removed at any time, while welded caps cannot.
Flange Cover Sealing Faces:
Flat Face (FF), Raised Face (RF), Male Face (MFM), Tongue and Groove (TG), Ring Joint (RJ)
10. Lined Flange Cover
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A lined flange cover is a type of blind flange where the side closest to the medium is welded with stainless steel, forming a single unit. Lined flange covers are used as blind flanges on pipelines carrying corrosive media. The difference between lined flange covers and ordinary flange covers is the addition of a corrosion-resistant lining on the surface in contact with the medium.
11. ASME Neck Welding Flange
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A neck welding flange is connected to the pipe end and is mainly used to connect pipes to each other. Slip-on-neck flanges have holes for bolts to pass through, allowing two flanges to be tightly connected. A gasket is used for sealing between the flanges.
A gasket is placed between the sealing surfaces of the two flanges. After tightening the nuts, the specific pressure on the gasket surface reaches a certain value, causing it to deform and fill the unevenness on the sealing surface, ensuring a tight, leak-proof connection. Flange connections are detachable connections and can be divided into vessel flanges and pipe flanges according to the components being connected. Slip-on-neck flanges are suitable for connecting steel pipelines with a nominal pressure not exceeding 2.5 MPa.
Slip-on-neck flanges are used for butt welding between flanges and pipes. They have a reasonable structure, high strength and rigidity, and can withstand high temperature and pressure, repeated bending, and temperature fluctuations, providing reliable sealing. Slip-on-neck flanges with a nominal pressure of 0.25–2.5 MPa use a raised face sealing surface.
12. ASME Standard Welding Neck Flange
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ASME flanges are parts used to connect pipes to each other, attached to the pipe ends. ASME (American Standard) welding flanges are manufactured using two methods: forging and casting.
ASME welding flanges can be further divided into necked and neckless types based on whether they have a neck.
An ASME welding flange consists of two flanges with a gasket, fastened together with bolts. ASME flanges have perforations; the bolts secure the two flanges together, and a gasket seals the gap between them.
3. Flange Types and Sealing Surface Forms
