As essential components in pipeline connections, flanges come in a wide variety, each with its own specific applications and advantages. Based on their form, flanges can be primarily categorized into slip-on flanges, butt-weld flanges, socket-weld flanges, threaded flanges, lap joint flanges, and blind flanges. The following details the characteristics, applications, advantages, and disadvantages of these flanges.
Slip-on flange (PL)
Slip-on flanges, also known as lap joint flanges, are a relatively simple flange type. They consist of two welded steel plates and are typically used to connect low-pressure pipelines. Their simple structure makes them easy to manufacture and install, and their cost-effectiveness makes them an ideal choice for applications where pressure and sealing requirements are low. However, due to their relatively simple structure, slip-on flanges may not offer the same sealing performance as other flange types, so caution is advised when selecting them for applications where sealing requirements are high.
Weld-neck flange (WN)
Weld-neck flanges consist of two butt-welded steel plates or forgings and are typically used to connect medium- and high-pressure pipelines. Weld neck flanges are welded together to securely connect the flange to the pipe, resulting in high strength and sealing performance. The sealing surface of a weld neck flange typically comes in various configurations, including raised face (RF), grooved face (MFM), and tongue-and-groove (TG), to accommodate varying operating pressures and media requirements. While the manufacturing and installation process is relatively complex and costly, weld neck flanges offer excellent performance in high-pressure, high-temperature, and high-stress environments, making them widely used in industries such as the petroleum, chemical, and shipbuilding industries.
Socket weld flange (SW)
A socket weld flange is welded to the steel pipe at one end and bolted to the other. It is commonly used in pipelines with a PN ≤ 10.0 MPa and a DN ≤ 40, and is suitable for use in industries such as boilers, pressure vessels, and the petroleum and chemical industries. The sealing surface of a socket weld flange is similar to that of a weld neck flange, and the appropriate sealing surface can be selected based on the operating pressure and media requirements. The installation process is relatively simple, saving material and cost. However, due to its structural characteristics, the sealing performance of a socket weld flange may be limited, so caution is advised when selecting a flange for applications requiring high sealing performance.
Threaded Flange (Th)
A threaded flange is a non-welded flange whose internal bore is machined into pipe threads, allowing it to connect to threaded pipes. Threaded flanges are easy to install and maintain, and can be used on pipelines where welding is not permitted. For example, in high or low temperature conditions, welding can pose a safety hazard, making threaded flanges an ideal choice. However, the sealing performance of threaded flanges can be affected by thread accuracy and fit, so careful selection is required in applications where sealing is critical. Furthermore, threaded flanges can leak under conditions of rapid pipe temperature fluctuations, so special care is required when using them.
Loose-fit Flanges
Loose-fit flanges, including butt-weld and flat-weld, are primarily designed to save materials or facilitate construction. Their structure allows for the use of different materials for the flange and pipe, allowing for the selection of the appropriate material combination based on actual needs. The advantages of loose-fit flanges include reduced manufacturing costs and ease of installation and maintenance. However, due to their structural characteristics, their sealing performance can be affected, so careful selection is required in applications where sealing is critical.
Blind Flange
A blind flange is a flange without a central hole, used to seal pipe plugs. Its function is similar to welded caps and threaded caps, and it is typically used at the end of a pipe system or where temporary plugging is required. Blind flanges can be installed by bolting or welding, making them easy to install and remove. During maintenance and repair of pipe systems, blind flanges can conveniently cut off the flow of media in the pipe, providing safety during repair work.
Other Special Flange Forms
In addition to the common flange types mentioned above, there are also several specialized flange types, such as carbon steel flanges, stainless steel flanges, alloy steel flanges, copper flanges, and plastic flanges. These flanges are primarily categorized by material, each with its specific applications and advantages. For example, carbon steel flanges offer excellent mechanical strength and corrosion resistance, making them suitable for general industrial use. Stainless steel flanges offer excellent corrosion resistance and high-temperature strength, and are commonly used in the chemical, petroleum, and food industries. Alloy steel flanges are suitable for applications under high-temperature and high-pressure conditions, exhibiting excellent mechanical properties and heat resistance. Copper flanges are commonly used to connect water pipes, while plastic flanges are suitable for connecting plastic pipes.
Furthermore, flanges can be categorized by their sealing surface type, including raised face (RF), grooved face (MFM), tongue-and-groove (TG), flat face (FF), and ring joint (RJ). The choice of these sealing surface types primarily depends on the operating pressure, media characteristics, and operating conditions. For example, raised face flanges are suitable for most applications; grooved face flanges are suitable for slightly higher pressure applications; tongue-and-groove face flanges are suitable for flammable, explosive, and toxic media and for higher pressure applications; flat face flanges are suitable for low pressure and non-toxic media applications; and ring joint flanges are used in specific high-pressure sealing applications.
In summary, there are many different types of flanges, each with its own specific application scenarios and advantages. When selecting a flange, it's important to consider factors such as specific project requirements, pipeline parameters, and media characteristics. Only by selecting the appropriate flange type and material can the safety and reliability of the pipeline system be ensured. Furthermore, during installation and use, strict compliance with relevant specifications and standards is essential to ensure the flange's sealing performance and service life.