1. Divided according to the chemical industry (HG) standard: Weld Neck Flange (WN), Threaded Flange (Th), Plate Flange (PL), Socket Weld Flange (SW), Blind Flange (BL), Ring Type Joint Flange (PJ/SE), Lap Joint Flange (PJ/RJ), Lined Flange Cover (BL(S)), and Flange Cover (BL) [2].

2. Categorized by petrochemical (SH) industry standards: Threaded Flange (PT), Weld Neck Flange (WN), Slotted Flange (SO), Socket Weld Flange (SW), Lug Flange (LJ), and Flange Cover (not specified).

3. Divided by mechanical (JB) industry standards: Weld Neck Flange, Blind Flange, Flat Weld Flange, Weld Ring Plate Loose Flange, Flat Ring Plate Loose Flange, Bevel Ring Plate Loose Flange, Flange Cover.

4. Divided by national (GB) standards: integral flange, threaded flange, socket weld flange, necked butt welding flange, necked socket welding flange, ring-type necked loose flange for welding, flat plate welding flange, ring-type flat plate loose flange for welding, flat ring flat plate loose flange, rolled ring flat plate loose flange, flange cover.