Based on the connection method with pipelines or equipment, common flanges mainly include the following types:

Slip-On Flange (SO): Also known as a sliding flange, the pipe is inserted into the flange's inner hole, and fillet welds are made on both the inner and outer sides of the flange neck. It has a simple structure, low cost, and low requirements for assembly alignment, making it widely used. However, compared to weld neck flanges, its strength is lower, making it unsuitable for extremely high temperatures, high pressures, or highly hazardous applications.

Weld Neck Flange (WN): Also known as a high-neck flange, its neck is butt-welded to the pipeline. This structure effectively disperses stress, thus providing the highest rigidity and enabling it to withstand harsh conditions such as high temperatures, high pressures, and large temperature and pressure fluctuations. It is commonly used in critical facilities in the petroleum, chemical, and power industries, but its price and installation costs are also higher.

Socket Weld Flange (SW): The pipe is inserted into the flange socket and fillet welded. It is suitable for small-diameter (DN≤40) high-pressure pipelines. The connection is robust, but it is not suitable for highly corrosive fluids.

Lap Joint Flange (LJ): Consists of a movable flange ring and a stub end welded to the pipe. The flange ring can rotate freely, facilitating bolt hole alignment. It is particularly suitable for pipelines requiring frequent disassembly and maintenance or those using expensive corrosion-resistant materials (such as stainless steel). Using only the stub end in a precious metal significantly reduces costs. However, its pressure resistance is limited, and it is typically used only for low pressure applications.

Threaded Flange (TH): The flange has threads machined into its inner bore, allowing direct screwing to a pipe with external threads without welding. Installation and disassembly are extremely convenient. However, due to the thread clearance, it is unsuitable for high-temperature, low-temperature, or drastically fluctuating pressure conditions to prevent leakage.

Integral Flange (IF): Typically cast as a single unit with equipment (such as pumps and valves). It is mostly used in high-pressure pipelines.

Blind Flange (BL): A flange without a central opening, specifically used to seal the ends of pipes or equipment openings, providing isolation and sealing.

Flanges are found in almost all industrial sectors involving fluid transport, such as:

Petrochemical industry: Connecting pipelines transporting crude oil, natural gas, and various chemicals.

Power industry: Connecting high-temperature, high-pressure steam pipelines for boilers, turbines, and other equipment.

Municipal engineering: Used in urban water supply, drainage, and heating networks.

Shipbuilding: Used for various piping systems within cabins.

Food and pharmaceutical industries: Used to connect sanitary-grade pipelines, ensuring a clean production environment.