Most pipe systems use pipe flanges to adjoin separate pipes and seal them together. Flanges look like rings or raised collars that skirt the pipe. The rings or collars allow for increased support at the connection points, and facilitate the attachment of additional components, like valves or gages.
Countless industrial, commercial, and manufacturing applications exist for flanges, and each type must adhere to exact standards. Before using a flange, it is best to consult a specialist or manufacturer to make sure the right flange is being used.
Standardized flanges and their components are used widely to facilitate easy disassembly and maintenance. Most shops will stock these commonly used products. However, local standards may not be compatible with each other.
Additionally, there are limitless specifications that determine what type of flange is most appropriate. Bore size, pressure class, pipe schedule and other specifications determine what is needed. Flanges are made with a broad range of materials. Metals such as carbon steel, stainless steel and aluminum are all used to meet different industrial requirements.
Carbon steel flanges often need to be individually manufactured by trained machinists. Automated CNC laths and other precision equipment are required to design flanges Each one must exactly conform to the necessary pipe schedule, bore size, and pressure class. The product that flows through the pipe also helps to determine what type of flange and materials are needed.
Suppliers often stock common types of pipe flanges. Examples include weld neck flanges, slip-on flanges, socket weld flanges, lap-joint flanges, blind flanges and threaded flanges. These are described below.
Weld Neck Flange
A weld neck flange is made by attaching the neck of the pipe directly to the flange using a butt weld connection. This relieves pressure from the pipe and transfers it to the flange. The weld neck provides good service for a variety of pressures.
Slip-on flanges slide over the pipe to be wielded when the flange is in place. The inside diameter of the flange is cut a bit wider than the outside diameter of the pipe. This allows for a snug fit. They are secured with fillet welds on both sides of the flange.
Socket Weld Flange
Socket weld flanges are often used on small pipes under high pressures. The outside of the pipe is connected to the flange with a fillet weld. The pipe’s terminating edge does not fit flush with the flange face. The space between the flange face and the pipe edge is called the “bottom clearance”.
The clearance allows for the welding material to expand upon cooling. This flange may not be appropriate for pipelines carrying corrosive material because cracks can develop around the clearance.
Lap-joint flanges are also called Van Stone Flanges. They include two separate components; the flange and its stub-end. The flange fits around a sub-end, which is then welded to the pipe. The flange itself is left free to rotate. This allows for a better fit or “pairing” between the two flange rings that connect the two pipes.
Most flanges are in the shape of rings with bolt holes near the edges. In these flanges, the pipe or stub end is fitted inside the flange. Blind flanges, however, are solid disks with no bore in the middle. They are not designed to connect two pipes, but to seal or cover a pipe’s end. They are employed to test a pipe’s pressure tolerance.
Threaded flanges have a thread around the inside so that they can be screwed onto a pipe. When welding is not possible threaded flanges can be used on low-pressure pipes systems.