Steel flanges are classified according to their structural form, sealing surface type, material, connection method, and applicable standards. Classification by structural type and standard is the most common and systematic.

Classification by Structural Type:

Flat-Welding Flanges (PL) are the most widely used and lowest-cost type in engineering. Their pressure ratings include European standards PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, and Japanese standards 5K and 10K.

Slip-On Flanges (SO) have superior pressure resistance and stiffness compared to flat-welding flanges due to their necked back. Their pressure ratings cover European standards PN6 to PN40, American standards 150LB to 1500LB, and Japanese standards 5K to 30K.

Welding Neck Flanges (WN) use butt welding connections and have high pressure resistance and wear resistance. They are suitable for high-risk working conditions. Their pressure ratings include European PN10 to PN160, American 150LB to 2500LB, and Japanese 5K to 30K.

Socket Welding Flanges (SW) have stepped inner diameters and are suitable for welding small-diameter pipes. Their pressure ratings cover European PN10 to PN100, American 150LB to 1500LB, and Japanese 5K to 20K.

Threaded Flanges (Th) use non-welded threaded connections and are easy to operate. They are suitable for low-pressure applications. Their pressure ratings include European PN6 to PN40, American 150LB and 300LB, and Japanese 5K to 20K.

Loose Flanges include weld-neck loose flanges (PJ/SE) and flat-weld loose flanges (PJ/RJ). These flanges are movable for easy installation and hole mating. Pressure ratings cover European PN6 to PN40, American 150LB to 600LB, and Japanese 5K to 20K.

Blind Flanges (BL) are used to seal the ends of pipes. They are removable and have wide pressure rating ranges, including European PN2.5 to PN160, American 150LB to 2500LB, and Japanese 5K to 30K.

Classification by Standard System:

Common standard systems for steel flanges mainly include European, American, and Japanese and Korean systems.

Representative standards of the European system include ISO 7005-1, DIN EN 1092-1, BS 4504-3.1, GB/T 9112~9125, HG/T 20592, JB/T 74~94, etc. Their pressure ratings are usually indicated by PN.

Representative standards of the American system include ASME B16.5, ASME B16.47, SH/T 3406, GB/T 9112~9125, HG/T 20615, etc. Their pressure ratings are usually indicated by Class (e.g., 150LB, 300LB).

Representative standards of the Japanese and Korean systems include JIS B2220, KS B1503, etc. Their pressure ratings are usually indicated by K (e.g., 5K, 10K).

Other Classification Dimensions

According to sealing surface form, they can be divided into flat (FF), raised face (RF), concave face (F), tongue and groove face (T/G), ring joint face (RJ), etc.

According to material, they can be divided into carbon steel flanges and alloy steel flanges, etc. Carbon steel flanges are widely used in ordinary environments, while alloy steel flanges are suitable for high-pressure or high-temperature environments.