Which flanges are most commonly used in pipes?

Standard flange

The type of flange used for piping applications depends primarily on the strength required for the flange joint. Use flanges or welded connections for easy maintenance (flange connections can be quickly and easily removed).

Welding flange

Welded flanges ("WN") use long tapered hubs for welding to pipes.

This flange type is commonly used in high pressure and high / low temperature applications that require unrestricted flow of fluids from the piping system (the holes in the flange match the holes in the pipe). There is no pressure drop to prevent negative effects, and metal near the flange joints can cause turbulence and corrosion. The tapered hub allows a smooth distribution of mechanical stress between the pipe and the weld neck flange and helps to perform radiographic inspections to detect possible leaks and welding defects. The size of the flange (NPS and piping table) should match the size of the connecting pipe.

Long welding neck flange

The long welding neck flange ("LWN") is similar to the welding neck flange, but the neck (tapered hub) extends and acts as a bore extension.

Long weld neck flanges are commonly used for containers, columns or barrels. These flange types are also available for heavy bucket (HB) and the same bucket (E) types.

Sliding flange

The sliding flange is connected to the pipe or fitting by two fillet welds, one for internal use and one for the outside of the flange cavity. The hole size of the sliding flange is larger than the outer diameter of the connecting pipe because the pipe must slide inside the flange to perform the connection by performing fillet welding. Sliding flanges are also defined as "hub flanges" and are easy to identify due to their slim and compact shape. In the long run, flanged connections made with sliding flanges are more fragile than welded flanged connections (under similar conditions of use). Welded flanges have tapered hubs and are not present in sleeve welded flanges. The mechanical stress between the pipe and the flange can be distributed more evenly. The welding neck joint has only one welding area instead of two (socket welding flange). Another advantage of the welding neck flange is that it can be connected to pipes and fittings. The socket welding flange is only suitable for pipes.

Threaded flange

Threaded flanges are connected to the pipe by screwing the pipe thread onto the flange without seam welding (in some cases, small welds should be used to increase the strength of the connection). Threaded flanges can be up to 4 inches in size and have a variety of pressure ratings, but they are mainly used for small pipes in low pressure and low temperature applications, such as water and air service. Threaded flanges are often used in places with special requirements, such as gas stations and factories, because welding connections in such environments can be dangerous.

Blind flange

Contrary to all flange types seen above, blind flanges do not have a central hole, which seals the pipeline valve and blocks the flow of fluid. Due to the system pressure and the required bolting force, the blind flange must withstand greater mechanical stress. The blind flange can be easily installed in the pipeline, and it can be easily dismantled. The constructor can install or maintain it in the pipeline terminal (this is also the reason why the blind flange is used as a pressure vessel access hole).