Flanges are integral parts of many engineering and plumbing projects. Used in many different fields, such as the transport (pipelines, ships) of petroleum, gas, water, etc., their manufacturing facilities and those of power generation, chemicals, and chemical fertilizers, flanges are of various kinds in type and shape, and their material too is diversified (low carbon steel, low alloy steel, stainless steel, high alloy steel, non-ferrous steel, or such) in accordance with the type of fluid and service environment.

A flange is a ring or collar, usually provided with holes for bolts, and screwed or welded over the end of a tube or pipe to permit other objects to be attached to it. Flanges are often used in plumbing, pipelines and construction zones. Flanges are very useful because they can be adapted to the needs of a project. If a pipeline needs to change course, for example, the flange can be removed and changed to accommodate the new pipeline channel. Flanges are also valuable because they serve as reinforcement for pipes, making them much stronger than they are on their own.

There are many different types of special flanges:

– Orifice flanges
– Spectacle blinds
– Long welding neck flanges
– Weldoflange/Nipoflange
– Expander flange
– Reducing flange
– Groove Flanges / Tongue Flanges

What are Orifice flanges?

Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gases in the respective pipeline. Pairs of pressure “Tappings”, mostly on 2 sides, directly opposite each other, are machined into the orifice flange. This makes separate orifice carriers or tappings in the pipe wall unnecessary.

Orifice Flanges generally come with either Raised Faces or RTJ (Ring Type Joint) facings. They are, for all intensive purposes, the same as weld neck and slip on flanges with extra machining.

The image on the right shows a set Orifice Flanges, where a Orifice Plate is mounted and a jack screw is machined. This jack screw is used to facilitate separating the flanges for inspection or replacement of the Orifice Plate and gaskets.

The range of orifice flanges covers all standard sizes and ranges, and all common flange materials. Flanges are available in Welding Neck, Slip On, and Threaded form, and are typically supplied with two 1/2″ NPT tappings in each flange.

ASME B16.36 covers Dimensions and dimensional tolerances from orifice flanges (similar to those covered in ASME B16.5) that have orifice pressure differential connections. Coverage is limited to the following flanges:

– WELDING NECK CLASSES 300, 400, 600, 900, 1500, 2500

Drawing of Orifice Flanges

What are Spectacle blinds?

Spectacle Blinds are generally applied to permanently separating pipesystems, or just to connect with each other. A Spectacle Blind is a steel plate cut into two discs of a certain thickness.
The two discs are attached to each other by section of steel similar to the nose piece of a pair of glasses. One of the discs is a solid plate, and the other is a ring, whose inside diameter is equal to that of a flange.

1. Spectacle blind 2. Flanges 3. Gaskets 4. Stud Bolts

Spectacle Blinds be applied in systems, which regularly need to be separated from other installations. Normally, a Spectacle Blind is mounted in the “open” position so that flow through the pipe is possible. If the Spectacle Blind in the “close” position is rotated, the pipe is blanked off and no flow is possible.

Maintenance on a pipesystem can be a reason to rotate the spectacle in the “close” position. This run will take place through the hole, that is drilled in the connection piece. By loosening of all bolts, and partial removal of their, the Spectacle Blind can be rotated. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.



Spades & Ring Spacers


Spades and Ring Spacers are basically the same as Spectacle Blinds, except that both are not attached to each other.

Spades and Spacers be applied in systems where maintenance is often not necessary, or in applications with large pipe sizes. Depending on the flange size and the Pressure Class, Spades can weigh hundreds of pounds. To prevent unnecessary weight to a flange connection, usually will be chosen not for a Spectacle Blind, but for 2 separate parts.


So as for the Spectacle Blind already described, maintenance on a pipesystem can be a reason to temporarily replace a Ring Spacer for a Spade. By loosening of all bolts, and half of the bolts temporarily remove, the Spade or Spacer can be placed. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.

A small problem is that we basically can not see, or a Spade or a Spacer mounted between the flanges. Therefore, the handles are often specially marked, or both have a different design; a customer often provides its own specification.

What should never lack is, that in the handle, the diameter and the Pressure Class of a Spade or Spacer is engraved; this applies also for the Spectacle Blind.

What are Long Welding Neck flanges?

Long Welding Neck Flanges (abbreviated LWN flanges) are similar to a standard Welding Neck flange, but the “Neck” is considerably longer. This type is often used as a nozzle for a barrel or column. In addition, there are the type LWN Heavy Barrel (HB) and the Equal LWN Barrel (E); they have a different shape and a thicker “Wall”.

Weldoflange / Nipoflange

The Weldoflange and Nipoflange is a combination of a Welding Neck flange and a supposedly Weldolet or Nipolet. The 2 components are manufactured in one piece, and not welded. These flanges are primarily in Branchconnections.

On the website of Promat BD you can find more information about the various performances, dimensions etc. Furthermore, they have an expanded range of special flanges, fittings and branch connections.

What are Expander flanges?

Expander Flanges is a Welding Neck pipe flange where the nominal size of the non-flanged end is larger than the nominal size of the flanged end. They can be used to change the size of a pipe run. These are usually used to increase the line size to the first or second larger size. This is an alternative to using a separate reducer and weld neck flange combination. The expander flange can be used to connect pipe to pumps, compressors and Valves.

What are Reducing Flanges?

Reducing Flanges are suitable for changing line size, but should not be used if abrupt transition would create undesirable turbulence, as at pump connections. A reducing flange consists of a flange with one specified diameter having a bore of a different and smaller, diameter. Except for the bore and hub dimensions, the flange will have dimensions of the larger pipe size.

What are Groove flanges / Tongue flanges?
A groove flange is constantly paired with a tongue flange.
The tongue flange has the face with a raised ring (i.e. the tongue). One flange has a machined raised ring (also called the tongue) and the other one has machined groove depression (also called the groove). Those two flanges should match perfectly with each other.
Tongue-and-groove facings are standardized in both large and small types. They are mainly used for pump covers and valve bonnets.
Tongue-and-groove joints have the advantage of being self-aligning and act as a reservoir for the adhesive. Major machining operation are not necessary especially thanks to the scarf joint keeping the oxis of loading in line.

Like most other industries, flanges have standards that they must meet in order to be sold and used it the field. Flanges manufactured in the United States are judged by ASME standards. Flanges that are made to ASME standards are usually made from forged materials. Flanges are important pieces of equipment that are used on most every construction site, pipeline and plumbing job in the world. These are just a few types of flanges to give you an idea of what to look for and how diverse flanges are. There are many flange manufacturers that provide very high-quality products. When choosing a manufacturing, be sure that the sales representative is knowledgeable about their inventory and the capabilities of their flanges.

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