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.
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.
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.
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:
- Flat welded — looks like a metal ring with holes in diameter. It is attached to the pipe by two welded seams around the circumference.
- 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.
- 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.
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:
- 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.
- 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.
- 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.
- 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.
- 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.
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”.
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.
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.
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.
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.
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.
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:
- To join two elements, flat parts are used that have a hole in the center where the end of the pipe is inserted.
- Holes are placed along the perimeter of the ring — fasteners are inserted into them: bolts or studs with nuts.
- 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.
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.
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:
- If the parts have 4 holes, then tighten the bolts crosswise.
- The surface of the structure must be degreased and checked for corrosion and rust.
- It is recommended to use only new gaskets, and they must be installed strictly in the center.
- The tightening force of the bolts must be uniform — this is the only way to ensure a reliable and tight flange connection.
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.