Flanges may take many forms: they may be strengthening ribs, like the flange of an I-beam, or guides, like the flange of a train’s wheel. However, one of the principal uses of the word “flange” refers to its use in plumbing as a means of joining pipes, valves or pumps. Typically, flanges are fixed to pipework systems with bolts, by soldering or through a combination of the two techniques.

Weld Neck Flanges
The weld neck, also known as a welding neck, consists of a ring shape that tapers into a protruding lip. This lip fits all the way around a pipe’s outside circumference, attached by welding. The pipe and flange have the same internal diameter, helping to reduce any turbulence or erosion within the pipeline.

Slip-on Flanges
The slip-on flange, as its name suggests, “slips” over the pipe like a ring on a finger. It is thickest around its innermost point, where it is fillet-welded to the pipe. A fillet-weld is approximately a triangular-shaped adhesion which joins two surfaces that meet at a right angle. One advantage of the slip-on flange is its relative ease of application and use.

Threaded Flanges
A threaded flange resembles the slip-on flange in its general shape. However, as its name indicates, a threaded flange has threading along its interior edge where it meets with the piping. Because this type of flange affixes by threading, you don’t need to weld it to the pipe. Less robust than other, welded types of flanges, the threaded flange works best for low-pressure applications.

Blind Flanges
A blind flange “blanks off” a pipe; as such, it’s also known as a blanking flange. You can easily distinguish a blind flange from the other types as its form resembles a cover or lid, a solid disc with slightly raised edges to weld around the circumference of the piping.

Lap Joint Flanges
A lap joint flange is “butt welded” to the pipe, meaning that instead of affixing a slightly larger flange around the pipe’s circumference, the two elements are joined end to end. It works best in low-pressure applications and has an advantage of being easy to align.

Socket Weld Flanges
A socket weld flange features an interior hole that is stepped, with one diameter on one side and another on the other side, which allows it to partially affix around the outside circumference of the pipe where it is welded. The flange then continues flush with the interior diameter of the piping, allowing free flow without friction or turbulence.