What is a flange

Flange, also known as flange disc. Flange is a part of the interconnection between shaft and shaft, used for the connection between the pipe ends; also used in the flange on the import and export of equipment, used for the connection between two devices, such as reducer flange. Flange connection or flange joint is a detachable connection consisting of flange, gasket and bolt interconnected as a group of combined sealing structure. Usually refers to a disk-like metal body with several fixed holes around the perimeter for connecting other components, which is widely used in various mechanical equipment and pipeline connections. Flange is a part of the interconnection between shaft and shaft, used for the connection between the pipe ends; also used in the import and export of equipment flange, used for the connection between two devices, such as reducer flange.
1. According to the chemical (HG) industry standards.
Integral flange (IF), threaded flange (Th), plate flange (PL),  welding neck flange (WN), slip on flange (SO), socket welding flange (SW), butt welding ring loose flange (PJ/SE), flat welding ring loose flange (PJ/RJ), lined flange cover (BL(S)), blind flange (BL) .
2. By petrochemical (SH) industry standards.
Threaded flange (PT), butt welding flange (WN), flat welding flange (SO), socket welding flange (SW), loose set flange (LJ), flange cover (not table note).
3. According to mechanical (JB) industry standards.
Integral flange, butt welding flange, plate type flat welding flange, butt welding ring plate type loose set flange, flat welding ring plate type loose set flange, flanged ring plate type loose set flange, flange cover.
4. According to the national (GB) standard points.
Integral flange, threaded flange, butt welding flange, necked flat welding flange, necked socket welding flange, butt welding ring with neck loose set flange, plate type flat welding flange, butt welding ring plate type loose set flange, flat welding ring plate type loose set flange, flanged ring plate type loose set flange, flange cover.

Standard of flange

Flange as a connection is widely used internationally, which requires a unified standard. For example, pipe flange now mainly has two standard systems, namely, Germany DIN (including the former Soviet Union) as the representative of the European pipe flange system (DIN, GB, JB, HG20592) and the United States ANSI pipe flange as the representative of the American pipe flange system (including ANSI, GB, HG20615). In addition, there are Japanese JIS pipe flanges, but they are generally used only for public works in petrochemical plants and have less influence in the international arena. Now the pipe flange of each country is introduced in the following.
1. The European flange system
European flange system: Germany DIN (including the Soviet Union) 
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.
Nominal diameter: 15~600mm.
Flange structure type: flat welding plate type, flat welding ring loose-fitting type, rolled edge loose-fitting type, butt welding rolled edge loose-fitting type, butt welding type, necked threaded connection type, integral type and flange cover.
Flange sealing surfaces: flat, concave, concave and convex, tongue and groove, rubber ring joint surface, lens surface and diaphragm welding surface.
The Soviet Union in 1980 released the OCT pipe flange with the record standard and the German DIN standard is similar.
2. The American flange system
American flange system: the United States ANSI B16.5 “steel pipe flange and flange fittings
Nominal pressure: 150psi (2.0Mpa), 300psi (5.0Mpa), 400psi (6.8Mpa), 600psi (10.0Mpa), 900psi (15.0Mpa), 1500psi (25.0Mpa), 2500psi (42.0Mpa).
Nominal diameter: 6~4000mm.
Structure type of flange: strip welding, socket welding, threaded connection, loose set, butt welding and flange cover.
Flange sealing surface: concave surface, concave-convex surface, tongue-and-groove surface, metal ring connection surface.
3. JIS (Japan Standard) pipe flange
JIS pipe flange: generally used only for public works in petrochemical installations, less influential in the international arena, and no independent system has been formed in the international arena.
4. GB (National Standard) system
China’s steel pipe flange national standard system GB .
Nominal pressure: 0.25Mpa ~ 42.0Mpa

  • Series 1: PN1.0, PN1.6, PN2.0, PN5.0, PN10.0, PN15.0, PN25.0, PN42 (main series). 
  • Series 2: PN0.25, PN0.6, PN2.5, PN4.0.

Among them, PN0.25, PN0.6, PN1.0, PN1.6, PN2.5, PN4.0 a total of six grades of flange dimensions belong to the European flange system represented by the German flange, the rest of the American flange system represented by the American flange. 
In GB standard, the maximum nominal pressure level belonging to the European flange system is 4Mpa, and the maximum nominal pressure level belonging to the American flange system is 42Mpa. 
Nominal diameter: 10mm~4000mm

Flange assembly

  • 1. Before assembling the flange, the flange surface must be cleaned, especially the sealing surface.
  • 2. When assembling the flat welding flange, the pipe end should be inserted into 2б▄3 of the inner diameter thickness of the flange, and then the flange should be spot welded to the pipe. If it is a horizontal pipe, the flange should be spot welded from above, and then the flange position should be checked and corrected from different directions with a 90бу angle ruler so that the sealing surface is perpendicular to the centerline of the pipe, and then the second point under spot welding is correct.
  • 3. Check and correct the flange position from the left and right direction with 90бу angle ruler, and complete the spot welding and fixing of the flange through the third and fourth spot welding afterwards.
  • 4. For the assembly of flange pairs, the bolt holes of the mounting flange should be aligned with the corresponding bolt holes of the fixed flange and parallel to the fixed flange, and the deviation should not be less than 1.5% of the outer diameter of each thousand flanges. And not more than 2mm.
  • 5. When choosing the matching flange of equipment or valve parts, attention should be paid to whether the flange of the original equipment or valve parts is the same size as the flange connection used in the pipeline.

Commonly used soft gasket materials

Rubber sheet and rubber wool sheet are the most commonly used flange soft gasket materials.
1. Industrial rubber sheet
Rubber sheet is commonly known as industrial rubber sheet, also known as industrial vulcanized rubber sheet or rubber sheet.
2. Rubber sheet
Rubber wool sheet, also known as asbestos rubber sheet, is generally used as a gasket for equipment and pipe flange sealing, and the medium can be water, steam, air, various gases, ammonia, lye and oil, etc.

Connection of flange

  • 1. The flange connection should be kept on the same axis, the deviation of the bolt hole center should not exceed 5% of the aperture, and the bolt should be freely perforated. The flange connection bolts should have the same specifications, the installation direction should be the same, and the bolts should be tightened symmetrically and evenly.
  • 2. Slant washers of different thicknesses should not be used to compensate for the non-parallelism of the flange. Do not use double gaskets. When large diameter gaskets need to be spliced, they should not be buttressed with flat ports, but should be in the form of slanting lap rings or labyrinths.
  • 3. To facilitate the installation and removal of the flange, the tightening bolt and flange surface should not be less than 200 mm.
  • 4. When tightening the bolt, symmetry and intersection should be carried out to ensure uniform force on the gasket.
  • 5. Bolts and nuts should be coated with molybdenum disulfide, graphite oil or graphite powder for subsequent removal of: stainless steel, alloy steel bolts and nuts; pipeline design temperature at 100буC or below 0буC; open-air facilities; atmospheric corrosion or corrosive media.
  • 6. Metal gaskets such as copper, aluminum and soft steel should be annealed before installation.
  • 7. Direct buried flange connection is not allowed. Buried pipe flange connection should have inspection wells. If it must be buried, anti-corrosion measures should be taken.

Source: China Flanges Manufacturer иC Yaang Pipe Industry (www.steeljrvs.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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