Flange connection is one of the most widely used connection methods in pipeline connection construction, and we often see its presence in daily life. For example, many natural gas pipelines and heating pipelines installed in residential areas use flange connections.

A flange connection is a detachable joint in which two pipes, fittings, or equipment are first fixed to a flange, and then a flange gasket is added between the two flanges. Finally, bolts are used to tighten the two flanges to tightly connect them.

Flanges can generally be divided into the following five types: flat welding flange, butt welding flange, socket welding flange, loose sleeve flange, and threaded flange.

1、 Flat welding flange

Flat welding flange refers to a type of flange that is connected to containers or pipelines using fillet welds. It belongs to any type of flange, and the flange ring has two types: with and without a neck. Flat welding flanges have a simple structure and use fewer materials during production, but their rigidity and sealing are not as good as those of butt welding flanges. They are widely used in the connection of medium and low pressure vessels and pipelines.

Flat welding flange with neck, flat welding flange without neck

2、 Butt welded flange

Butt welding flange generally refers to a flange with a neck and a circular pipe transition, which is connected to the pipeline by butt welding. Welding flanges have the characteristics of being less prone to deformation, good sealing, and corresponding rigidity and elasticity. Its welding joint is far from the joint surface, and the joint surface will not deform due to welding temperature, so it is currently widely used in pipeline welding.

Welding flanges are generally suitable for pipelines with significant pressure or temperature fluctuations, as well as pipelines with high, high, and low temperatures. They are also suitable for pipelines transporting expensive, flammable, and explosive media.

3、 Socket welding flange

Socket welding flange refers to a flange that is inserted into the flange ring step at the end of the pipe and welded at the end and outside of the pipe. Socket welding flanges have good rigidity, small welding deformation, and good sealing performance, and can be used in situations with pressures ranging from 1.0 to 10.0MPa.

4、 Loose flange

Loose flange, also known as looped flange, is a type of flange that uses flanges, steel rings, etc. to wrap the flange around the pipe end. The flange can move around the pipe end. The steel ring or flange is the sealing surface, and the function of the flange is to press them tightly. It can be seen from this that due to being blocked by steel rings or flanges, the loose flange does not come into contact with the medium, making it easier to disassemble and assemble the pipeline.

Loose flange is suitable for connecting non ferrous metals such as steel and aluminum, as well as stainless and acid resistant steel containers, and for corrosion-resistant pipelines.

5、 Threaded flange

A threaded flange is a type of non welded flange that processes the inner holes of the flange into threads and connects them with threaded pipes. Compared to plain welded or butt welded flanges, threaded flanges are easier to install and maintain, and can be used on pipelines that are not allowed to be welded on site. Its advantage is that it does not require welding, and the additional torque generated by flange deformation on the cylinder or pipeline is very small. The disadvantage is that the flange thickness is large, the cost is high, and it is suitable for connecting high-pressure pipelines. However, under conditions of rapid temperature changes in pipelines, it is not recommended to use threaded flanges to prevent leakage.