1. Categorized by the chemical industry (HG) standard: Flanged Joints (IF), Threaded Flanges (Th), Plate Weld Flanges (PL), Socket Weld Flanges (WN), Slip-on Flanges (SO), Blind Flanges (SW), Ring Type Joint Flanges (PJ/SE), Socket Weld Ring Flanges (PJ/RJ), Lined Flange Covers (BL(S)), Flange Covers (BL) [2].

2. Categorized by petrochemical (SH) industry standards: threaded flange (PT), weld neck flange (WN), flat welding flange (SO), socket welding flange (SW), loose joint flange (LJ), and flange cover (not specified).

3. By mechanical (JB) industry standard classification: Flanged Joints, Welding Neck Flanges, Plate Welding Flanges, Welding Ring Plate Loose Flanged Joints, Flange Ring Plate Loose Flanged Joints, Bevel Ring Plate Loose Flanged Joints, Flange Covers.

4. Categorized by national (GB) standards: Welding Neck Flange, Threaded Flange, Blind Flange, Lap Joint Flange, Socket Welding Flange, Ring Type Joint Flange with Welding Neck, Plate Flange with Lap Joint, Ring Type Joint Plate Flange, Plate Flange with Ring Joint, Flange Cover.