What are the application scenarios for flanges with various standards?
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Our factory specializes in fine chemicals; in other words, we produce synthetic resins, and as a result there are many pipes and valves, so numerous that it’s like a forest. All the flanges used in the factory’s construction in 2007 were socket weld flanges. By the way, are there also metric and imperial versions of socket weld flanges? For example, with DN50 and 2 inches: DN50 seems to not fit into a 2-inch pipe, but the inner diameter of a 2-inch flange is larger enough to allow it to fit in. I recently visited a paint factory built by a competitor; their manufacturing process is the same as ours, but the new factory uses neck flanges everywhere. I asked if that doesn’t result in high costs He said that although it’s a bit more expensive, it saves labor costs, as there’s no need to weld short pipes for things like elbows and tees. After working with them for so many years, the disadvantages of flat welding flanges are obvious: they cannot be used a second time. After being welded, if they are removed and tried to be reused, the flanges tend to crack easily. Additionally, in applications where temperatures reach 280 degrees, flat welding flanges are prone to leakage.
The petrochemical industry makes extensive use of butt-welded flanges; slip-welded flanges are hardly used there. Production in this industry is continuous, and any leakage could lead to the shutdown of the facility. Since the additional investment involved can be considered negligible, WN or IF flanges are preferred. Slip-welded flanges are used for smaller pipelines
I. Plate flat welding flanges: Advantages: Easy to obtain materials, simple to manufacture, low cost, and widely used. Disadvantages: Poor rigidity; therefore, they cannot be used in chemical process piping systems where there are requirements for resistance to stress, in environments with flammable or explosive substances, or in situations requiring high vacuum levels, as well as in highly hazardous environments. The seal surface types include flat and convex surfaces. II. Welded flanges with a neck: Advantages: Easier to install on-site, as the process of damaging the welds due to handling can be omitted. Disadvantages: The neck of these flanges is relatively short, which reduces the flange’s stiffness and load-bearing capacity. 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. III. 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 substances, flammable and explosive materials, and toxic gases. Disadvantages: Wafer 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. IV. Integral Flange: The integral flange is a type of flange connection method. It also belongs to the category of welded steel pipe flanges with a neck. 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 pipelines with 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 levels of hazard, sealing surfaces other than RF faces, such as male-female faces (MFM) and tongue-and-groove faces (TG), can be used. V. Socket Weld Flanges: Socket weld flanges are flanges in which 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). Application areas: 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. VI. 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. Advantages: Compared to butt-weld flanges or slip-on 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: Under conditions of rapid changes in pipe temperature, or when the temperature is above 260°C or below -45°C, it is recommended not to use threaded flanges to avoid leaks. VII. 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: 1. Cost savings. When the pipe material is special and expensive, welding flanges of the same material is costly as well. 2. It is not suitable for welding or processing, or it requires high strength. Such as plastic pipes, glass fiber pipes, and the like. 3. Easy to construct. For example, when connecting, it may be difficult to align the flange bolt holes, or there might be changes in those bolt holes over time as the equipment is replaced. Disadvantages: 1. Low stress resistance. 2. Low strength at the weld ring (especially when the thickness is 3 mm or less). VIII. 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, and that end is formed into a flange; the flange part is then fitted over this flange. Advantages: 1. It is easy to weld or process, and it provides high strength when required, such as in plastic pipes and fiberglass pipes. 2. It facilitates construction; for example, when connecting, the alignment of the flange bolt holes is easier, which also helps to prevent any changes in those bolt holes if the equipment needs to be replaced in the future. 3. Save costs when prices are high. 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, whereas welded end caps cannot. Flange cover sealing surfaces: flat (FF), raised face (RF), male and female face (MFM), tongue and groove face (TG), ring joint face (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.