What is a flange: specifications and application


It is not always con­ve­nient to use welds on pipeline ele­ments. In some places, instal­la­tion of addi­tion­al prod­ucts is required — valves, pumps. Then a flange comes to the res­cue — a spe­cial part designed to con­nect pipes where weld­ing is not suit­able. They are clas­si­fied by size, mate­ri­als of man­u­fac­ture, sur­face type and oth­er cri­te­ria.

Flange — definition of the concept

Accord­ing to the ter­mi­nol­o­gy guide, a flange is a flat piece with holes that pro­trudes as a con­nect­ing part of pipes. Studs, bolts and oth­er fas­ten­ers are attached to the holes of the part to help fix it on the pipeline. The dimen­sions of the flanges cor­re­spond to the diam­e­ter of a par­tic­u­lar pipe, so the man­u­fac­tur­er often pre-equips the pipe with such an ele­ment.

Flange type

The main require­ment for con­nect­ing pipes is tight­ness: this cri­te­ri­on is pre­cise­ly pro­vid­ed by the flange. It reli­ably tight­ens parts, gives the con­nec­tion reli­a­bil­i­ty, strength, and the abil­i­ty to use it in a wide tem­per­a­ture range. If time­ly main­te­nance is car­ried out, the flange con­nec­tion will last for many years. This type of part is man­u­fac­tured in accor­dance with GOST, there­fore, spe­cial require­ments are imposed on it.

Design features of flanges

Today, flanged pipe con­nec­tions are one of the most pop­u­lar and sim­ple con­nec­tions that allow you to quick­ly and reli­ably join parts. This is due to the design fea­tures:

  • round (rarely square) shape;
  • the pres­ence of small holes around the perime­ter;
  • flat design;
  • the pres­ence of a cen­tral hole.
Draw­ing exam­ple

The part is in demand when assem­bling a pipeline due to its sim­plic­i­ty and speed of work. The user needs to insert the flange onto a pipe of the desired diam­e­ter, and then screw it to the same fix­ture on anoth­er pipe if two parts are joined. Often, pipe man­u­fac­tur­ers already equip the prod­uct with a flange at the end, which sim­pli­fies the work. Flange repair is required when defects are present on the sur­face or the seal­ing of the joint is bro­ken.

Where are flanges used?


This type is used to assem­ble the pipeline, the instal­la­tion of any flange occurs only if there is a pipe of the appro­pri­ate diam­e­ter. There are sev­er­al areas of appli­ca­tion of the part:

  • assem­bly of civ­il cen­tral pipelines;
  • assem­bly of gas pipelines;
  • instal­la­tion of domes­tic water sup­ply sys­tems;
  • instal­la­tion of heat­ing mains;
  • assem­bly of indus­tri­al sys­tems and com­mu­ni­ca­tions.
flange con­nec­tion

These parts can be ele­ments of a pipe, shaft, fit­ting or body part. This is a uni­ver­sal prod­uct that, when con­nect­ed to anoth­er part, is able to pro­vide tight­ness. The ele­ment with­stands high tem­per­a­ture and pres­sure, so this type of fas­ten­ing can be used in gas and water pipelines. The para­me­ters by which they are select­ed are the dimen­sions, the shape of the seal­ing sur­face, as well as the method of fas­ten­ing.

Main types of flanges

The first clas­si­fi­ca­tion by which all types can be divid­ed is con­struc­tive. Accord­ing to her, there are such main types:

  1. Flat weld­ed — looks like a met­al ring with holes in diam­e­ter. It is attached to the pipe by two weld­ed seams around the cir­cum­fer­ence.
  2. Col­lar — in addi­tion to holes in diam­e­ter, it is also equipped with a skirt for weld­ing. Easy to install, as it is fixed with one weld.
  3. Free on the weld­ed ring — con­sists of two ele­ments: a flange and a ring with the same diam­e­ter and pres­sure. The ring is fixed on the pipe by weld­ing, and the flange remains free, which ensures ease of instal­la­tion.
Vari­eties of steel prod­ucts

These types of flanges are used for join­ing pipeline fit­tings and equip­ment. To more specif­i­cal­ly deter­mine the area where the part is used, the mate­r­i­al of its man­u­fac­ture will help.

What is the item made from?


In indus­try, steel flanges are used, but the steel from which the part is made also varies. The mark­ing of steel flanges will deter­mine in what con­di­tions it is bet­ter to use this part:

  1. Steel 20 is the most used raw mate­r­i­al. This is car­bon steel, parts from it are used to assem­ble fit­tings on high­ways, where the exter­nal tem­per­a­ture is not low­er than ‑40 degrees, and the inter­nal indi­ca­tors are not high­er than +475 degrees.
  2. Steel 09g2s — steel from alloys of nick­el, chromi­um and molyb­de­num, designed for weld­ing. Prod­ucts from this mate­r­i­al can be oper­at­ed at an exter­nal tem­per­a­ture of ‑70 degrees.
  3. 12X18H10T — cryo­genic steel. Parts made of this mate­r­i­al can be used in aggres­sive envi­ron­ments, such as alka­lis and acids. Per­mis­si­ble tem­per­a­ture from ‑196 degrees to +350 degrees.
  4. 10X17H13M2T — cor­ro­sion-resis­tant ordi­nary steel. Fas­ten­ers from it are oper­at­ed in espe­cial­ly extreme con­di­tions, because it remains resis­tant to cor­ro­sion under stress. Oper­at­ing tem­per­a­tures from ‑196 to +600 degrees.
  5. 15X5M — low-alloy heat-resis­tant steel. Such prod­ucts have a high resis­tance to oxi­da­tion at rates of + 600–650 degrees.

These brands are the most used, but in addi­tion to them, man­u­fac­tur­ers use oth­er raw mate­ri­als. There are polypropy­lene mod­els — they are designed for join­ing polypropy­lene pipes with met­al valves. The oper­at­ing tem­per­a­ture of such mate­r­i­al is much low­er — +80 degrees. They can be sup­plied with a col­lar for a flange — a spe­cial part for cre­at­ing a flange con­nec­tion made of polypropy­lene.

Polypropy­lene flange

In addi­tion to steel and propy­lene, two types of cast iron are used — mal­leable and gray. Duc­tile iron parts are used at oper­at­ing tem­per­a­tures from ‑30 to +400 degrees, and gray cast iron parts are used at tem­per­a­tures from ‑15 to +300 degrees.

Flange pressure classes

Parts man­u­fac­tured accord­ing to Asme (Asni) stan­dards are always char­ac­ter­ized by a num­ber of para­me­ters. One of these para­me­ters is the nom­i­nal pres­sure. In this case, the diam­e­ter of the prod­uct must cor­re­spond to its pres­sure accord­ing to the estab­lished sam­ples. The nom­i­nal diam­e­ter is indi­cat­ed by a com­bi­na­tion of the let­ters “DU” or “DN”, fol­lowed by a num­ber char­ac­ter­iz­ing the diam­e­ter itself. Nom­i­nal pres­sure is mea­sured in “RU” or “PN”.

Flange draw­ing with var­i­ous des­ig­na­tions

The pres­sure class­es of the Amer­i­can sys­tem cor­re­spond to the con­ver­sion to MPa:

  • 150 psi — 1.03 MPa;
  • 300 psi — 2.07 MPa;
  • 400 psi — 2.76 MPa;
  • 600 psi — 4.14 MPa;
  • 900 psi — 6.21 MPa;
  • 1500 psi — 10.34 MPa;
  • 2000 psi — 13.79 MPa;
  • 3000 psi — 20.68 MPa.

Trans­lat­ed from MPa, each class will indi­cate the flange pres­sure in kgf / cm². The pres­sure class deter­mines where the select­ed part will be used.

Surface types


This type of con­nect­ing fas­ten­er can also be divid­ed accord­ing to the type of seal­ing sur­face. They are:

  • A — plane;
  • B — con­nect­ing pro­tru­sion;
  • F — depres­sion;
  • E — pro­tru­sion;
  • D, M — groove;
  • C, L — spike;
  • K — for lens gas­ket;
  • J — for an oval sec­tion gas­ket.
Sur­face fin­ish­es

These types of GOST were adopt­ed recent­ly, while it is not­ed that the type of sur­face C, L, and E are pro­duced only at the request of the cus­tomer and are not stamped.

Protrusion Height

If you look at the draw­ing of a steel flange, then it has sev­er­al para­me­ters, includ­ing the height of the ledge. It is denot­ed by the let­ters H and B, it can be mea­sured in all types of prod­ucts, except for the one that has an over­lap con­nec­tion. The fol­low­ing should be remem­bered:

  • pres­sure class 150 and 300 mod­els will have a 1.6 mm pro­tru­sion height;
  • pres­sure class 400, 600, 900, 1500 and 2000 mod­els have a 6.4 mm pro­tru­sion height.
With pro­tru­sion and depres­sion


In the first case, sup­pli­ers and man­u­fac­tur­ers of parts take into account the sur­face of the pro­tru­sion, in the sec­ond case, the sur­face of the pro­tru­sion is not includ­ed in the spec­i­fied para­me­ter. Parts brochures may list these fig­ures in inch­es, where 1.6 mm is 1/16 inch and 6.4 mm is ¼ inch.

Geometry and specific gravity of products

An impor­tant para­me­ter that deter­mines the geom­e­try is the con­di­tion­al pas­sage of prod­ucts. As already not­ed, it is denot­ed by the let­ters “DU” and has indi­ca­tors from 10 to 200. This con­cerns the choice of the required part: when the user knows Du, all oth­er dimen­sions are assigned to the flange auto­mat­i­cal­ly. For exam­ple, for a DN 50 mod­el, the indent height will be 57–59; DN 80 this fig­ure is 89–91, and DN 100 — 108–110, where the first dig­it indi­cates the inner diam­e­ter of the pipe or pipe, and the sec­ond — the out­er diam­e­ter.

Flat flange draw­ing

Anoth­er impor­tant indi­ca­tor is the weight of the flanges. It depends not only on vol­umes, dimen­sions and height, but also on its geom­e­try, mate­r­i­al of man­u­fac­ture. It is worth giv­ing an exam­ple: a flange accord­ing to GOST 12820–80 with DN 100 of a flat type has a weight of 2.85 kg, while a flange of the same diam­e­ter, but of a col­lar type accord­ing to GOST 12821–80 has a weight of 4.4 kg. It fol­lows from this that col­lar flanges have a greater mass than flat parts.

How is a flange connection made?

When it is nec­es­sary to con­nect two parts of the pipeline, weld­ing of a steel flange to the pipe is used. This fix­a­tion is called a flange con­nec­tion and in the future makes it pos­si­ble to dis­as­sem­ble the pipeline in order to car­ry out repairs. To under­stand how the assem­bly takes place, it is nec­es­sary to con­sid­er the process in detail:

  1. To join two ele­ments, flat parts are used that have a hole in the cen­ter where the end of the pipe is insert­ed.
  2. Holes are placed along the perime­ter of the ring — fas­ten­ers are insert­ed into them: bolts or studs with nuts.
  3. The con­nec­tion will be detach­able so that it is air­tight using gas­kets. A flange con­nec­tion is designed to join two pipes or con­nect a pipe to a tank equipped with a flanged inlet pipe.
An illus­tra­tive exam­ple of a flange con­nec­tion

You can make a flange with your own hands — such a detail is per­fect for a sharp­en­er for a machine for sharp­en­ing objects.

Joint production tools

To inde­pen­dent­ly con­nect two pipe parts, you need to pre­pare tools. Basi­cal­ly, this is equip­ment designed for tight­en­ing bolt­ed con­nec­tions around the cir­cum­fer­ence of the flanges:

  • man­u­al key;
  • cap key;
  • pneu­mat­ic impact wrench;
  • hydraulic torque wrench;
  • hydraulic type bolt ten­sion­er.
Dock­ing on pipes


In addi­tion, a spe­cial lubri­cant is required, which is applied to both sur­faces to avoid fric­tion of parts and ensure ease of torque. The sequence of work is sim­ple: first, the first bolt is tight­ened, then they pro­ceed to the twist of the one that is 180 degrees diag­o­nal­ly from the first. Next, they move on to the bolt locat­ed at an angle of 90 degrees from the sec­ond, and from it to the oppo­site.

Tips from the masters

There are a num­ber of use­ful rec­om­men­da­tions from pro­fes­sion­al crafts­men that will help you deal with a flange con­nec­tion the first time:

  1. If the parts have 4 holes, then tight­en the bolts cross­wise.
  2. The sur­face of the struc­ture must be degreased and checked for cor­ro­sion and rust.
  3. It is rec­om­mend­ed to use only new gas­kets, and they must be installed strict­ly in the cen­ter.
  4. The tight­en­ing force of the bolts must be uni­form — this is the only way to ensure a reli­able and tight flange con­nec­tion.
Con­nect­ed pipes with flanges

In order to remove the flange in the future, spe­cial machines are used to help bore it and open the bolts. It is dif­fi­cult to remove the parts man­u­al­ly, so pneu­mat­ic tools are used.

Con­nect­ing pipes with flanges is a con­ve­nient and reli­able type of join­ing of two parts. It helps in the future to repair the pipeline by remov­ing the con­nect­ing ele­ments, while weld­ing will not allow this pro­ce­dure to be car­ried out. It is select­ed in strict accor­dance with the work­ing con­di­tions, tem­per­a­ture and pipe diam­e­ter.


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