Industrial Pipe Flanges, Bolts and Gaskets Guide

Industrial Flanges, Bolts and Gaskets

Typically disc-shaped, flanges are used to connect two pipe pieces or a pipe with another component within a system such as a valve, pressure vessel or pump. Also referred to as pipe flanges, flanges feature bolt holes around the rim, edge or collar. Gaskets are usually placed between the flanges to create a tight seal. 

While it is easy enough to weld two pipes together, once connected in this way they are difficult to disassemble. On the other hand, if flanges, bolts and gaskets are used to connect the pipes, the seal is not just leak-proof but also simple to disassemble for cleaning or inspection. Flanges feature different connection types. These include threaded flanges, slip-on flanges, socket weld flanges and welded neck flanges. Meanwhile, blind flanges are used to close the end of a pipe.  

Different flanges can withstand different pressure ratings from 10 to 170 bars. Flanges are commonly prefixed by a PN, or pressure nominal, number. For example, PN16 flanges are designed to withstand 16 bar of pressure. Flanges are often made from stainless steel due to the material’s high-pressure resistance. Stainless steel flanges are also more popular than those made from carbon steel since they are more corrosion resistant. There are different pipe flange standards. For example, AS 2129 table D flanges and table E flanges are available in different diameters and feature a different number of bolts and bolt sizes. 

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Flange Bolts 

Commonly found in plumbing systems and automotive applications, flange bolts feature a skirt or a flange under the bolt head. This helps to distribute the clamping load to deliver a better mating surface thus ensuring a safer and faster production. 

Weld Neck Flanges

Designed to withstand high pressures, weld neck flanges feature a long neck that is butt welded to a pipe. The bore of the flange and pipe match to minimise any erosion. World neck flanges are larger than most other pipe flanges. They are popular in piping systems with multiple bends and have a high life expectancy. 

Blind Flanges 

Blank flanges are used to seal the end of a pipe or a fitting that is not in use. Blank flanges are often composed of a full-faced or stub flange, a couple of backing rings, a gasket and a fastener set. 

Threaded Flanges 

Also sometimes called screwed flanges, threaded flanges feature a threaded bore that is fitted on a pipe with a matching thread, eliminating the need for welding. While threaded flanges are relatively simple to install, they are not suitable for high-pressure or high-temperature systems. As such, they are a good option for smaller and less complicated pipe systems.   

Lap Joint Flanges 

Also called loose flanges, lap joint flanges feature two parts, including a joint stub that is butt welded to the pipe. While they are not suitable for high-pressure systems, lap joint flanges are ideal for piping systems that may need to be frequently dismantled.

Slip-On Flanges 

Slip-on flanges feature larger diameters than the pipes they are connected to. Once placed over a pipe, slip-on flanges are welded from both the inside and the outside. Slip-on flanges are a good solution for low-pressure applications. 

Socket weld flanges 

Similar to slip-on flanges, socket weld flanges feature a female socket. Once the pipe is fitted into the socket, the seal is fillet welded from the outside.  Socket weld flanges are commonly utilised in small bore piping systems. 


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Pipe flanges can be classified into the following types: flat face, raised face, ring joining. 

  • Flat face flanges are commonly used with flat-faced counter-flanges. They are usually used with full face gaskets. 
  • Raised face flanges feature a small raised area around the bore. The height of the raised area is contingent on the pressure and temperature rating of the flange. 

  • Ring joining face flanges feature a grove where the gasket is placed. They are typically used in high-pressure and high-temperature piping systems.

Flanges and pipes are usually connected by welding. The flange can also be screwed onto the pipe to achieve a threaded connection. Welded connections are generally used in high-pressure and high-temperature applications while threaded connections are more suitable for low pressures and systems that do not experience high temperatures. Threaded connections are also commonly used in pipes that are under two inches in diameter and experience vibration, contraction or expansion. 

Flange bolts feature a skirt that extends from beneath the head to create an even distribution of force across a surface. Flange bolts are often used in plumbing to secure two pipes together and mechanics to connect parts such as transmissions and engines. They are also commonly found in electronics. Flange bolts can be made from a variety of materials including carbon and alloy steel for high-temperature applications, and anodised aluminium and stainless steel for corrosion resistance. Both zinc chromate flange bolts and cadmium-plated flange bolts are decent options for most environments.

Pipes with flanges usually do not offer a tight seal. Gaskets contour to the shape of the flanges to create a seal between two sections of a piping system, preventing any liquid or air leaks. Flange gaskets come in three general types: non-metallic flange gaskets, semi-metallic flange gaskets and metallic flange gaskets. 

  • Non-metallic flange gaskets are used in low-pressure and low-temperature applications. They are generally made from a soft material that fills the grooves of the flange face. 
  • Also referred to as composed flange gaskets, semi-metallic flange gaskets are made from both metal and non-metal materials. These materials can include graphite, PTFE, stainless steel or another alloy. Semi-metallic flange gaskets are used in a variety of pressure and temperature applications.  

  • As their name suggests, metal flange gaskets are made entirely out of metal such as stainless steel, carbon steel or another alloy. Metal flange gaskets are normally used in high-pressure and high-temperature applications. 

Piping systems feature different types of hydraulic and pneumatic fittings. Here are just some of the more popular ones. 

  • Elbow industrial pipe fittings are used to alter the direction of flow between two pipes. Most elbow fittings come with either 45 or 90-degree angles. While elbow fittings usually come with female threads, they can also be butt welded.  

  • Reducer industrial pipe fittings are used to connect pipes that feature different diameters. There are two types of reducer fittings. Cone-shaped concentric reducers and eccentric reducers with an edge that is parallel to the connecting pipe. 

  • Tee industrial pipe fittings are T-shaped elements with one inlet and two outlets (or two inlets and one outlet). 

  • Cross industrial pipe fittings feature four openings that are connected to pipes. This type of pipe fitting is common in sprinkler systems.  

  • Coupling industrial pipe fittings are used to connect two straight pipes with the same diameter. They are commonly used to prevent leaks in damaged pipes. 
  • Union industrial pipe fittings are very similar to couplings, the main difference being that union fittings can be removed after installation while couplings cannot. They are commonly used when a piece of piping has to be removed for maintenance. 

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