There are seven standard types of flanges used for connecting pipes, valves, pumps and other parts of a pipe system: weld neck, slip-on, blind, socket weld, threaded, lap joint and ring type joint. For ease of comprehension, these flanges are divided into three categories: low turbulence, low pressure and other; however, these categories are not binding, as certain types of flanges may be adjusted for different applications.

Definition
A flange is a plate type device, normally round, that is attached to the end of a pipe, fitting, valve or other object to facilitate the assembly and disassembly of a piping system, providing easy access for cleaning, inspecting or modification. Flanges are usually welded or screwed in place, and all types except the lap joint have a raised face equal to the contact area of the associated gasket.

Low Turbulence Flanges
A weld neck flange is welded into the neck of the pipe system, matching the bores of both pipe and flange, which reduces turbulence and erosion inside the system. A socket weld flange is counter-bored to match the bore of the pipe before being welded in place; like a weld neck flange, the socket weld flange reduces turbulence and provides good flow characteristics.

Low Pressure System Flanges
Threaded flanges (also known as “screwed” flanges) are used in low-pressure pipe systems to connect other threaded components; no welding is necessary. Lap joint flanges are also used in low pressure pipe systems; they are easy to assemble and align and are the only type of flange that doesn’t have a raised face.

Other Types
A slip-on flange is slipped over the pipe and then welded in place; the strength of a slip-on flange is about two thirds that of a weld neck flange. A blind flange (sometimes referred to as “blanking flange”) is used to close off (“blank off”) pipes or valves. Ring type joint flanges use a metal ring that is compressed into a hexagonal groove on the face of the flange, ensuring a leak-proof seal in high pressure pipe systems.

Subcategorization by Face Type
Flanges may be subcategorized by different face types: flat face, raised face, ring-type joint, tongue and groove and male and female.