Flange knowledge

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Flanges are divided into threaded flanges and welded flanges. For low-pressure applications with small diameter threaded flanges, welded flanges are used for high-pressure and low-pressure applications with large diameter flanges. The thickness of the flanges, as well as the diameter and quantity of the connecting bolts, vary depending on the pressure level. 　　Depending on the different pressure levels, flange gaskets are made from various materials, ranging from low-pressure asbestos gaskets and high-pressure asbestos gaskets to metal gaskets. 　　1. Classified by material, they include carbon steel, cast steel, alloy steel, stainless steel, copper, aluminum alloy, plastic, acrylic, PPC, etc. 　　2. Classified by manufacturing method, they can be divided into forged flanges, cast flanges, welded flanges, and rolled flanges (for extra-large sizes). 3. Classified by manufacturing standards, they include national standards (Ministry of Chemical Industry standards, petroleum standards, power industry standards), American standards, German standards, Japanese standards, Russian standards, etc. 　　Several international systems for flange standards 1. Flange connections or flange joints refer to a detachable connection that consists of a flange, gaskets, and bolts working together as a combined sealing structure. Pipe flanges are those used in piping systems, while flanges on equipment refer to the inlet and outlet flanges of that equipment. 　　2. Several international systems for pipe flange standards
1) European flange system: German DIN (including the Soviet Union)
a. Nominal pressure: 0.1, 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.4, 10.0, 16.0, 25.0, 32.0, 40.0 MPa
b. Nominal diameter: 15–600 mm
c. Flange types: flat weld plate type, flat weld ring loose sleeve type, folded edge loose sleeve type, butt weld folded edge loose sleeve type, butt weld ring loose sleeve type, butt weld type, necked threaded connection type, integral type, and flange cover
d. Flange sealing surfaces: flat surface, concave surface, male and female surface, tenon and groove surface, rubber ring connection surface, lens surface, and diaphragm welding surface
e. The OCT pipe flange standard issued by the Soviet Union in 1980 is similar to the German DIN standard, so it will not be discussed further.

2) American flange system: American ANSI B16.5 “Steel Pipe Flanges and Flanged Fittings”, ANSI B16.47A/B “Large-Diameter Steel Flanges”
a. Nominal pressure: 150 psi (2.0 MPa), 300 psi (5.0 MPa), 400 psi (6.8 MPa), 600 psi (10.0 MPa), 900 psi (15.0 MPa), 1500 psi (25.0 MPa), 2500 psi (42.0 MPa)
b. Nominal diameter: 6–4000 mm
c. Flange types: strip weld, socket weld, threaded connection, loose sleeve, butt weld, and flange cover
d. Flange sealing surfaces: concave surface, male and female surface, tenon and groove surface, metal ring connection surface

3) JIS pipe flanges: These are generally used only in utility systems within petrochemical plants; they have little influence internationally and do not form an independent system on the global scale. 　　3. The **standard system for steel pipe flanges in China: GB 　　1) Nominal pressure: 0.25 Mpa~42.0 Mpa 　　a. Series 1: PN1.0, PN1.6, PN2.0, PN5.0, PN10.0, PN15.0, PN25.0, PN42 (main series) 　　b. Series 2: PN0.25, PN0.6, PN2.5, PN4.0 　　The flange sizes for the 6 grades of PN0.25, PN0.6, PN1.0, PN1.6, PN2.5, and PN4.0 belong to the European flange system represented by German flanges, while the others belong to the American flange system represented by American flanges. 　　In GB standards, the highest nominal pressure class for those belonging to the European flange system is 4 Mpa, while for those belonging to the American flange system, the highest nominal pressure class is 42 Mpa. 　　2) Nominal diameter: 10mm~4000mm 　　3) Structural types of flanges: 　　Integral flange 　　Unit flange 　　a. Threaded flange 　　b. Welded flange – Butt-welded flange, Waisted butt-welded flange, Plate-type butt-welded flange 　　c. Loose-flange – Butt-welded ring loose-flanged waisted flange, Butt-welded ring loose-flanged plate-type flange, Butt-welded ring loose-flanged plate-type flange, Plate-type flipped loose-flange 　　d. Flange cover (blind-hole flange) 　　e. Rotating flange 　　f. Anchored flange 　　g. Clad/welded flange 　　4) Flange sealing surfaces: Flat surface, Concave surface, Convex-concave surface, Tenon-and-socket surface, Ring-connected surface