A pipe flange is a disc, collar or ring which is attached to the pipe for the goal of providing additional strength, support, blocking the flow of a pipeline or adding more parts to it. Typically they are welded or screwed to the end of the pipe and connected to the bolts. To provide a tighter seal a gasket is inserted between the two mating flanges. These flanges are either custom-made with customer-provided specifications or are manufactured according to standard sizes. These pipe flanges are available in different types.
Most Commonly Used Flange Types
Slip-on pipe flanges slide over the pipe. Typically, they are machined with an inner diameter slightly larger compared to the outer diameter of the pipe. This allows the flange to slide over the pipe, but still to have a somewhat snug fit. Slip-on is fastened to the pipe with a fillet weld at the top and bottom of the flange. They are further classified as a ring or a hub. Rings and hubs are both considered slip-on flanges because they fit over the pipe.
Weld Neck Pipe Flanges are installed by welding the pipe to the flange’s neck. This enables the transfer of stress from the flange to the pipe itself. This also minimizes the concentration of high stress at the hub base. Weld necks are often used for high-pressure applications. The inner diameter of this connection is machined to match the inner diameter of the pipe.
Blind pipe flanges are used to fasten the end of the pipe system or the opening of the pressure vessel to prevent flow. They are commonly used for pressure testing of liquid or gas flow through a pipe or vessel. They often facilitate access to the pipe in the event that work needs to be done inside the line. Blind pipe flanges are mostly used for high-pressure applications.
Lap joint pipe flanges fit over the pipe and are most frequently used with Stub End Fittings. Typically, the pipe is welded to the Stub End and the Lap Joint is free to rotate around the stub end. The advantage of this is that there will be no problems with the alignment of the bolt hole. They have mostly used applications requiring frequent dismantling.
Threaded pipe flanges are identical to slip-on, except that the threaded pipe flange bore has tapered threads. They are used with pipes with external threads. The benefit of these is that it can be attached without welding. Threaded pipe flanges are often used for small diameter, high pressure requirements.
Socket-weld pipe flanges are frequently used in smaller sizes of high-pressure pipes. These flanges are connected by inserting the pipe into the end of the socket and applying the fillet weld around the top. This enables a smooth bore and a better flow of fluid or gas inside the pipe.