What is a Flange? The nuts and bolts of Flanges
What is a Flange?
A Flange is a protruding rim used to connect Pipes, Pipe components, Valves or other equipment securely.
It has two main components: a Flange face and Flange connection holes. These holes are used to connect Flanges to another surface (with a flat or slightly raised gasket) and are tightened with bolts or nuts.
Flanges are used in piping systems to provide pressure or fluid sealing to securely fasten the equipment in place. They increase strength at the joint and often allow for fast disassembly. With these access points, inspections or modifications can be carried out much easier than otherwise.
Manufactured by standards such as ANSI/ASME, these standards define the dimensions, shapes, and locations of the connection holes. The type of Flange you choose will depend on the details of your system, such as pressure capacity and application.
Keep reading for an exploration on the different types of Flanges, standards and industry uses!
Why do we use Flanges?
Flanges provide several benefits when utilised in Piping and other systems, thus their widespread use:
Durability
Flanges provide resistance against pressure and temperature within piping systems.
Sealing
Flanges seal at the joint, preventing unwanted leaks of liquids or gases within pipelines. This is important for safe operations and environmental protection.
Ease of Assembly and Maintenance
Flanges allow for easy assembly and disassembly of Pipe or equipment when repairs, maintenance, or modifications are needed, providing a significant advantage for production continuity and efficiency.
Flexibility
Flanges enable transitions between different pipe diameters, pressure classes, or materials. They are used at joints of different components or systems to bring together various elements and ensure compatibility.
Types of flanges
Threaded
A threaded Flange is mounted on the outer circumference of the Pipe or equipment and has a threaded inner surface.
The threaded structure allows the Flange to be held together with the connection point by tightening and loosening bolts or nuts.
They are easy to assemble and can be quickly disassembled by tightening and loosening bolts or nuts.
Used in low-pressure systems on smaller Pipes with thick walls, threaded Flanges allow you to connect and disconnect Pipe without disrupting the entire system for maintenance. In addition, you can avoid welding in most cases.
Recommended for:
Flammable, hazardous or explosive applications where welding is dangerous;
Restricted spaces where welding Flange to Pipe is not possible.
Not recommended for:
High-pressure applications.
Socket-weld
Socket-weld Flanges have a connection where you insert the Pipe into the Flange.
A multi-pass filet weld helps secure the connection and eliminate the constraints of threaded ends, making them easier to set up than other welded Flanges.
To set up, the Pipe is inserted in the socket of the Flange. When it reaches the bottom of the Flange, the Pipe is lifted out slightly by 1/16" (1.5mm) and welded. This gap allows for thermal expansion created by welding, reducing the probability that the weld will crack.
Recommended for:
Small-size and high-pressure piping that do not transfer highly corrosive fluids, i.e. Hydraulic Pipes.
Not recommended for:
Highly erosive or corrosive applications, as the gap is vulnerable to corrosion between the Pipe end and the socket’s shoulder.
Slip-on
Slip-on Flanges are used to secure, support, and absorb thermal expansions of Pipe ends.
They allow the Pipe to move freely while reducing stresses in the system.
These are thinner than most other Flanges, with an inside diameter slightly larger than the Pipe’s outside diameter. The Flange slips onto the Pipe and a fillet weld is applied at the top and bottom.
The welds enhance strength and prevent leakage. The speed at placing the Flange on the Pipe saves costs, but those savings are reduced with the additional costs of two fillet welds which are needed for proper installation.
Recommended for:
Low pressure industrial applications;
Cooling and firefighting water lines;
Process lines for oil, gas and steam.
Not recommended for:
Applications with high bending moments or severe temperature fluctuations.
Lap joint
Lap joint Flanges feature a two-piece design, including the butt welding of the stub end to the Pipe and the use of a backing Flange to create the connection. The backing Flange is typically made of different materials and is used to provide alignment and support.
As this Flange never comes into contact with the fluid, it is highly durable and can be re-used.
Recommended for:
Low-pressure applications;
When frequent dismantling for maintenance is required.
Not recommended for:
Extreme or high-pressure temperature applications.
Weld-neck
A Weld-neck Flange is mounted on the outer circumference of the Pipe or equipment at the joint and butt welded.
It is designed to provide a stronger and more durable connection, and is used in high-pressure and high-temperature applications.
The Flange’s bore matches that of the pipe, reducing turbulence and erosion. This connection relocates stress to the Pipes, ensuring a decrease in high-stress concentration at the bottom of the Flange, providing excellent strength and resistance to deformation under pressure.
Recommended for:
High-pressure and high-temperature applications;
Piping systems with repeating bends;
In conditions with wide fluctuations in temperature and pressure;
Systems with volatile and hazardous fluids;
Process piping.
Blind
Blind Flanges are solid discs that provide a seal by covering Pipe ends, used for terminating or isolating Piping systems.
These Flanges act as plugs, preventing leaks and ensuring a safe working environment and are used when future expansion or maintenance might be required.
These Flanges make it easier and more cost efficient to carry out pressure tests. You can also simply stop the flow of fluid and safely add new Pipes or new lines to pipelines.
Without blind Flanges, shutdowns and repairs would be incredibly difficult to handle. In addition, Blind Flanges are installed with bolts, so they’re also easy to remove.
Recommended for:
Testing pipe pressure;
Creating access points to piping systems;
Sealing a piping system temporarily to make repairs, or permanently.
Specialty Flanges
The flange types listed above are the most common. However, there is a range of additional Flange types available to suit a range of uses and environments:
Expanding flanges
Nipo Flanges
Reducing flanges
High hub flanges
Ring type flanges
Groove and tongue flanges
Loose flanges
Spectacle blind flanges
Long Neck Welding Flanges
Orifice Flanges
Stirlings stocks an excellent range and depth of Flanges in our warehouses, and we can obtain any specialty Flanges from our trusted suppliers.
Face types
Flat Face (FF)
Flat Face Flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.
The gasket surface is the same plane as the bolt frame, covering the Flange from its inside diameter to outside diameter.
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These are designed to avoid the bending that Flanges undergo as bolts are torqued.
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Raised Face (RF)
These common Flanges feature a small raised section around the bore with an inside bore circle gasket.
The raised face concentrates more pressure on a smaller gasket area. In turn, this increases the joint’s pressure containment capability.
Ring Joint Face (RTJ)
Used in high-pressure and high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal. The Flanges seal when the bolts are torqued, compressing the gasket between the Flanges into the grooves.
Tongue and Groove (T&G)
These Flanges feature matching grooves and raised sections. This aids in installation as the design helps the Flanges to self-align and provides a reservoir for gasket adhesive.
Male & Female (M&F)
These Flanges use a matching pair of grooves and raised sections to secure the gasket. Unlike tongue and groove Flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.
Standards and markings
Flanges fall under different global standards. At Stirlings we stock those falling in with the standards established by the American Society of Mechanical Engineers (ASME): ASME B16.5 & B16.47.
All flanges must include markers, typically on their outer perimeter.
Manufacturer logo or code
e.g Stirlings
ASTM material code
e.g ASTM A182
Material Grade
e.g 2205
Service rating (Pressure-temperature Class)
e.g CL150 / Table E / PN16
Size/Nominal Bore
e.g 15Nb
Thickness (Schedule)
e.g SCH40S
Choosing a Flange for your project
So which of these do we use on our project? This is determined based on specific standards and design parameters. General approaches include:
Pressure Class and Size
Flange dimensions are determined based on the pressure class and size of the pipeline being used. The pressure class should be selected to withstand maximum pressure. The dimensions of the Pipe, such as the outer diameter and inner diameter, are also considered.
Pipeline Material
Flange dimensions are also determined based on the material of the pipeline being used. Different materials, such as steel, Stainless steel, and carbon steel, have different dimension standards.
Tolerances
Tolerances are also considered in Flange dimensions. These represent acceptable deviations within a specified range.
Considering these factors when selecting the appropriate Flange dimensions is important to ensure a safe and compatible Pipe connection.
Industries
Where can you find all these Flanges in use? They are vital in a number of industries, including the following:
Petrochemical Industry
Flanges are used at the joints of pipelines in refineries, chemical plants, and petrochemical facilities.
Power Generation
Flanges play an important role in power generation facilities, including power plants, nuclear plants, hydroelectric plants, and thermal plants. They are used at the joints of pipelines, pumps, turbines, and other equipment.
Marine Industry
In the shipbuilding and marine industry, Flanges are used between pipelines, cooling systems, fuel systems, and other marine equipment.
Water and Wastewater Treatment
Flanges are widely used in water treatment plants, wastewater treatment plants, and sewer systems, used to establish connections between pipelines, pumps, valves, and other equipment.
Construction and Manufacturing
Flanges are used in the construction of industrial facilities and manufacturing processes, providing secure connections at the joints of pipelines, air ducts, equipment, and structural components.
So, what now?
We hope this summary of Flanges was helpful - but don’t worry! You don’t need to be an expert on Flanges and their uses, that’s our job! Whatever your Flange or piping system needs, check out our product range and Online Shop to make your order and get in touch for any help you may need.
A rhyme for your time:
Need a way to connect all your Pipe? Flanges will never make you gripe!
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