How to use the flange connection​ correctly

What is flange connection?

Flange connection is to fix two pipes, pipe fittings or equipment on a flange, and between the two flanges, with flange pads, bolted together to complete the connection. . Some fittings and equipment have their own flanges and are also flanged. Flange connection is an important connection method for pipeline construction. The flange connection is easy to use and can withstand large pressures. In industrial pipes, in the home, the pipe diameter is small and low pressure, and the flange connection is not visible. If you are in a boiler room or production site, there are flanged pipes and equipment everywhere.

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Types of flanges:

Generally low-pressure small-diameter wire-bonding flanges, high-pressure and low-pressure large-diameter welded flanges, the thickness of the flanges of different pressures and the diameter and number of connecting bolts are different.
Depending on the grade of pressure, the flange pads are also available in different materials, from low pressure asbestos pads, high pressure asbestos pads and PTFE pads to metal pads.
The flange connection is easy to use and can withstand large pressures.

In industrial pipes, the use of flange connections is very extensive, such as in the indoor fire hydrant water supply system, the connection of various valves and pipes such as butterfly valves, gate valves and check valves.

Materials for Flanges
Pipe flanges are manufactured in all the different materials like stainless steel, cast iron, aluminium, brass, bronze, plastic etc. but the most used material is forged carbon steel and have machined surfaces.
In addition, flanges, like fittings and pipes, for specific purposes sometimes internally equipped with layers of materials of a completely different quality as the flanges themselves, which are “lined flanges”.
The material of a flange, is basically set during the choice of the pipe, in most cases, a flange is of the same material as the pipe.
All flanges, discussed on this website fall under the ASME en ASTM standards, unless otherwise indicated. ASME B16.5 describes dimensions, dimensional tolerances etc. and ASTM the different material qualities.

Flange connection methods:

Flange connection methods can generally be divided into five types: flat welding, butt welding, socket welding, loose sleeves, and threads.
The first four are elaborated below:
1. Flat welding: only welding the outer layer, no need to weld the inner layer; generally used in medium and low pressure pipelines, the nominal pressure of the pipeline is lower than 0.25MPa. There are three kinds of sealing surfaces for flat welding flanges, which are smooth, concave and convex, and grooved. Among them, the smooth application is the most widely used, and the price is affordable and cost-effective.
2. Butt welding: The inner and outer layers of the flange should be welded. Generally used in medium and high pressure pipelines, the nominal pressure of the pipeline is between 0.25 and 2.5 MPa. The sealing surface of the welding flange connection method is concave-convex, and the installation is complicated, so the labor cost, the installation method, and the auxiliary material cost are relatively high.
3. Socket welding: generally used in pipes with nominal pressure less than or equal to 10.0MPa and nominal diameter less than or equal to 40mm.
4. Loose sleeves: Generally used in pipelines where the pressure is not high but the medium is corrosive, so the flanges are highly resistant to corrosion and the materials are mostly stainless steel.
This connection is mainly used for the connection of cast iron pipes, rubber-lined pipes, non-ferrous metal pipes and flange valves, and the connection between process equipment and flanges is also flanged.
Features of the connection method:
The main features of the flange connection are easy disassembly, high strength and good sealing performance. When installing the flange, the two flanges are required to be parallel, the sealing surface of the flange should not be damaged, and it should be cleaned. Flange gaskets should be selected according to design regulations.

Flange connection process:

F37 Flaring Connection - How to use the flange connection​ correctly

First, the connection between the flange and the pipe must meet the following requirements:

1. The center of the pipe and flange should be on the same horizontal line.
2. The sealing surface of the pipe center and the flange is 90 degrees vertical.
3. The position of the flange bolts on the pipe should be consistent.
Second, the pad flange gasket, the requirements are as follows:
1. In the same pipe, the gaskets with the same pressure should be the same, so that they can be exchanged later.
2. For pipes with rubber sheets, the gaskets are also preferably rubber, such as water lines.
3, the selection principle of the gasket is: as close as possible to the small width selection, which is the principle that should be followed in the premise that the gasket will not be crushed.
Third, the connection flange
1. Check the specifications of the flanges, bolts and gaskets to meet the requirements.
2, the sealing surface should be kept smooth and tidy, no burrs.
3. The thread of the bolt should be complete and there should be no defects. The fitting should be natural.
4, the texture of the gasket should be flexible, not easy to aging, the surface is not damaged, wrinkles, scratches and other defects.
5. Before assembling the flange, clean the flange to remove oil, dust, rust and other debris, and clean the seal line.
Fourth, the assembly flange
1. The flange sealing surface is perpendicular to the center of the pipe.
2. Bolts of the same specifications are installed in the same direction.
3. The flange installation position on the branch pipe should be more than 100 mm from the outer wall surface of the riser, and the distance from the wall of the building should be 200 mm or more.

4. Do not bury the flange directly in the ground, it is easy to be corroded. If it must be buried underground, it must be treated with anti-corrosion treatment.

Source: Network Arrangement – China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (

(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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