Flange type and code

Haha, when I first started working in the factory, I was indeed confused by the term “flange” – it sounded like a person’s name! It is actually a transliteration of the English word “Flange”; in simple terms, it refers to that circular disc or ring-shaped component found on the inlet and outlet parts of pipes, valves, and equipment, with rows of bolt holes that are used to connect those components to other elements. The types you listed above are quite comprehensive; they are all the most commonly used in the chemical and petrochemical industries. Their “codes” or “type codes” are, in drawings, standards, and technical documents, usually not represented by complex Chinese characters but rather by abbreviated letters or numbers for quick identification. Below, I will go over the types you mentioned, along with their most common codes (primarily based on the national standards GB/T 9112–9124 series as well as the common notation methods used in the chemical industry): --- ### **Flange Types and Their Common Code Correspondences** 1. **Plate Welding Flange** * **Code**: **PL** (Plate) * **Features**: The most commonly used and cheapest type. It’s just a ring plate that is welded directly to the tube. It has a simple structure, but its rigidity is slightly poor, and the pressure cannot be too high. 2. **Wafer flange with neck** * **Code**: **SO** (Slip-On) or **WN** according to HG/T 20592 standard (Note: In Chinese standards, wafer flanges with neck are denoted as SO, while those with butt joints are denoted as WN; however, older standards or certain industry practices may vary, so the specific standard should be followed.) * **Features**: It has a short neck in addition to the plate structure, which increases the flange’s strength and stiffness; it resists deformation better than plate-type flanges and is therefore more widely used. 3. **Weld neck flange** * **Code**: **WN** (Weld Neck) * **Features**: It has a long, sloping \"high neck\" that is welded to the pipe. It has the best strength and stiffness among all flanges, and is suitable for harsh operating conditions such as high temperatures, high pressures, toxic and harmful environments, as well as flammable and explosive situations. The price is also the highest. 4. **Integral Flange** * **Code**: **IF** (Integral Flange) * **Features**: The flange is forged or cast as one piece with the equipment’s housing, valve body, pump body, etc., resulting in extremely high strength. It is commonly used in equipment such as pumps, valves, and compressors. 5. **Socket Weld Flange** * **Code**: **SW** (Socket Weld) * **Features**: The pipe is inserted into the socket of the flange, and welds are applied externally at the corners. Suitable for small-diameter pipes (DN≤50); it is more reliable than threaded connections, but there is a risk of crevice corrosion after welding. 6. **Threaded Flange** * **Code**: **Th** (Threaded) or **PT** (Tapered Pipe Thread) * **Features**: The inner hole of the flange is threaded, allowing it to be screwed directly onto pipes with external threads. It is easy to install and does not require welding; it is commonly used in situations where welding is not allowed (such as oxygen pipelines) or with galvanized steel pipes. But its sealing performance is not as good as that of welded flanges. 7. **Plate Jacket/Slip-on Flange** * **Code**: **PJ/SE** (Plate Jacket/Slip-on for Stub End), or simply referred to as a **slip-on flange**; the plate jacket portion is called **SE** (Stub End). * **Features**: The flange itself is not welded directly to the pipe, but is instead fitted over the already welded \"plate jacket\". The flange can rotate freely, facilitating bolt hole alignment. The advantage is easy installation, and the flange material (such as stainless steel) and the pipe material (such as carbon steel) can be different to save costs. 8. **Flat-welded ring loose-flange** * **Code**: **PJ/PR** (Plate Jacket/Plate Ring) or **loose-flange**; the flat-welded ring portion is essentially the ring plate. * **Features**: The principle is the same as above, except that the ring used is a flat-welded ring (similar to a plate-type one), and its strength is lower than that of a butt-welded ring loose-flange. 9. **Flange cover** * **Code**: **BL** (Blind Flange) or **Cover plate** * **Features**: It has no holes in the middle; it is used to seal the end of a pipe or a device opening, serving as a \"blind plate\" that provides isolation and sealing. It is also used for system pressure testing, reserved ports, etc. 10. **Lined flange cover** * **Code**: **BL(S)** or **BL(L)** —— Indicates the lining material based on BL; for example, S stands for stainless steel lining, while L stands for rubber lining, etc. * **Features**: A layer of corrosion-resistant material (such as fluoroplastics, rubber, or stainless steel) is applied to the sealing surface and working surface of the flange cover, enabling use in corrosive media while providing both sealing and corrosion protection. --- ### **Quick memorization tips ** * **Look at the neck**: No neck means **PL**, a short neck means **SO**, and a long neck means **WN**. * **Check the connection: the thread type is **Th**, welding after insertion is **SW**, and those used for external fitting are **loose sleeves (PJ)**. * **Looking at the overall picture: those that are integrated with the device are called **IF**. * **Depending on the use: those used to block pipes are called **BL**. **Important note**: These codes may vary slightly across different standards (such as the American standard ASME B16.5, the Chinese standard GB, and the Ministry of Chemical Industry standard HG). In practical work, **it is essential to first check which standard is referenced in the drawings or technical documents**, and then look up the code regulations in that standard; this is the most accurate approach. Take it easy at the beginning of working; as you see more, you’ll naturally become proficient. From now on, when the experienced worker says “use a WN flange” or “get a BL to seal that opening”, you’ll know exactly what to do! .

Well written; it’s right to check the standard first and then the code. There are also Compact integral flanges, Hanger Flange suspension flanges, Swivel rotating flanges, TaperLok tongue-type sealing flanges, SAE 37°Flare flare flanges, method flanges, and so on – the choice depends on the specific application environment.