1. Divided by the chemical industry (HG) standards: 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)), Flange Cover (BL) [2].

2. Divided according to the petrochemical (SH) industry standards: threaded flange (PT), welding neck flange (WN), flat welding flange (SO), socket welding flange (SW), loose joint flange (LJ), and flange cover (not specified).

3. Divided by mechanical (JB) industry standards: Welding Neck Flanges, Socket Weld Flanges, Flat Weld Flanges, Ring Type Joint Flanges with Welding Neck, Ring Type Joint Flanges with Flat Weld, Beveled Ring Type Joint Flanges, and Flange Covers.

4. By country (GB) standards: whole flange, threaded flange, socket weld flange, slip-on flange with neck, socket weld flange with neck and loose fit, flat welding ring flange with neck and loose fit, plate flat welding flange, flat welding ring plate loose fit flange, flat welding ring plate loose fit flange, beveled ring plate loose fit flange, flange cover