Flanges are used to connect pipes, ducts, rail wheels and power transmissions. It is a good way to connect equipment, valves and components in a system line.
The use of flanges is often more flexible than when welding and it is the second most commonly used joining method after welding .
At Nordic Steel, we often use flanges when manufacturing ventilation ducts, equipment for oil and gas or aquaculture and maritime industries. The flanges are used to connect ducts, pipes or equipment and come in different sizes and shapes.
In this article, we look at flanges in the ASTM and DIN standards, which are the most common standards. It is also flanges in these standards that we use the most at Nordic Steel and in the industries we supply.
A typical flange connection consists of three parts:
Flanges are made of most materials. The material of the flange is usually the same as the system, or better. This is often governed by the specifications of the system. The material is selected based on media and influence.
Mixing of different material qualities should be avoided in order to maintain the correct voltage sequence. In some cases, grades are mixed, but then flanges and bolts with sleeves are often insulated. This is to avoid direct contact and avoid unwanted corrosion.
Flanges must be suitable for their intended use and fit the system in which they are to operate in. It is not the case that one size fits all.
Here are some of the most common flange types in ASTM standard (ANSI, ASME), commonly used in the oil and gas industry:
Weld-neck flange / collar flange / welding flange
Collar flanges are a leading choice for joining. The flanges have a relatively high performance and density in systems with oscillations and can be used in high-pressure and high-temperature systems. Like several other flanges, collar flanges require welding or pressing for installation on the pipe.
Blind flanges
Blind flanges are used for terminating or insulating pipe systems and are mainly boltable shiny washers, with or without packing surface. When installed correctly and combined with the correct gaskets, they can achieve a satisfactory seal that is easy to remove when needed.
threaded flanges
The flanges are also known as a threaded, threaded and screwed flange. This type of flange has internal threads that fit with the pipe's external threads. Such a connection means that in many cases you can avoid welding. Threaded coupling is often used in smaller dimensions and in systems with lower pressures.
Socket-weld flanges
Socket-weld flanges are ideal for smaller pipe diameters in low-temperature and low-pressure scenarios. These feature a connection where you place the pipe in the flange and then secure the connection with a simple weld. This allows this type of flange to be simpler than traditional weld-neck/collar flanges, as well as achieving a better joint than threaded flanges.
Slip-on flanges
Slip-on flanges are common and available in most sizes. This flange is adapted to the outer diameter of the pipe and threaded on. The flange must be welded to the pipe on both sides.
Lap Joint Flanges
Lap-joint flanges are basically a two-part construction. To achieve a seal, it must be installed over a collar. If the pipe does not already have a collar, it is first welded onto a stub-end. This design is often used in systems with limited physical space or systems that require frequent disassembly and maintenance.
Special flanges
The flange types shown above are the most common. However, there are a number of other flange types that are tailored to specific applications and environments. Other options include nipo flanges, weldo flanges, expanding flanges, compact flanges and reducing flanges.
The most common flange types in the DIN standard are flanges that are often used in different types of industries.
Loose flanges
Loose flanges make it possible to connect pipes or parts without welding them. The flanges are fastened with bolts and nuts, both to adjust the tightness and to simplify repair and inspection. It is also easier to install and remove the flanges for inspection and maintenance. Loose flanges come in different types, both with smooth end (RF), raised end (RTJ) and tapered end (MFM). Each type has specific properties and applications.
Plate flanges
Plate flanges are flat printed plates with a circular opening in the center. They act as a connection between pipe sections, valves or equipment. Plate flanges are easy to manufacture and are often less expensive than other flanges. The flat surface makes the flanges particularly suitable for use where high pressure or temperature is not a concern. The flanges are fastened using bolts and nuts, and can also be used in conjunction with a gasket to ensure tight connections and prevent leakage.
Welding flanges / welding flanges with collar
Welding flanges provide a permanent connection between two pipes or fittings. The flanges are attached by welding, which is both solid and leak-free. Welding flanges are typically used where sealing and strength are important, especially in high-pressure and high-temperature conditions. Special types of welding flanges have an elevated collar around the center of the flange. They provide extra strength to the connection between the pipes. The collar provides a natural guide to perform the welding operation and the pipe is welded to the raised collar. These flanges can also be used with a gasket to ensure a tight connection.
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Blind flanges
Blind flanges are used to seal or cover an opening in a piping system or container. It is designed to temporarily shut off a pipeline or equipment. Blind flanges are often used during maintenance and inspection, or when a particular section of the piping system is not in use. They are installed by bolting and are tight, to prevent leakage of liquids or gases.
Threaded flanges
Threaded flanges have internal threads that allow you to screw them directly onto pipes or equipment. The threads can be either internal (female) or external (male), depending on the type of flange. The flanges are typically used to connect pipes together when it is necessary to be able to dismantle them. This makes them suitable for pipes that need to be maintained or modified. They come in different standards and often use sealant, gaskets or tape in the threads before installation.
Bulkhead flanges
Bulkhead flanges are used in pipelines to separate two sections of the pipeline. The flanges have a plate with a circular opening and this opening is usually smaller than the pipe diameter. Bulkhead flanges are used to regulate the flow of liquids or gases in different parts of the pipeline. They can also be used to isolate or shut off a section of the pipeline for maintenance or repair. Bulkhead flanges can be fixed or removable and they play an important role in controlling and regulating fluid flow in various industries.
The face is another part that has a great impact on the performance of the flanges.
Common packing surfaces include:
Many gasket faces also offer one of two surfaces, rough or smooth.
In general, smooth gasket surfaces work best with metallic gaskets. Rough gasket surfaces create stronger friction with soft gaskets.
Flange dimensions also help to influence flange choices, both when it comes to design, maintenance or upgrading.
Common considerations:
Flanges are often classified according to their ability to withstand temperatures and pressures.
Pressure is indicated using a number and either "#", "lb" or "class" suffix, or "PN". The suffixes are interchangeable but vary based on region or supplier.
Common classifications in ASTM and DIN include:
Exact pressure and temperature tolerance varies depending on the type of material used, flange design and flange size.
Several types of flanges are regulated under global standards such as the American Society of Mechanical Engineers (ASME) - ASME B16.5 & B16.47.
Standard flanges are marked or stamped with the necessary technical information at the outer edge. This information is the same as in the product certificate. The embossing often has the following information:
