What is Flange: Everything You Need To Know

Ever wondered how complex piping systems manage to stay intact and function smoothly? The answer often lies in the humble flange. Flanges are essential components that connect pipes, valves, pumps, and other equipment, forming the backbone of many industrial systems.

In this guide, we’ll break down everything you need to know about flanges, from their types and uses to the materials they’re made from and the standards they adhere to.

Whether you’re an experienced engineer or simply curious, this comprehensive overview will help you understand the crucial role flanges play in various industries.

What Is A Flange?

What is Flange

A flange is a protruded rim or collar used to strengthen a structure or create a flanged connection between two components through bolts, welding, or threading. In industrial and plumbing applications, flanges are essential for facilitating easy assembly, disassembly, and maintenance of piping systems. They provide a secure, leak-free connection between pipes, valves, or other equipment, ensuring efficient fluid handling and structural integrity.

Characteristics of Threaded Flanges

Flanges exhibit several key characteristics that make them essential components in industrial and plumbing applications:

1. Strength and stability:

Flanges are designed to provide structural reinforcement and stability to connections between pipes, valves, and other equipment. They help distribute mechanical stress evenly, reducing the risk of leaks or failures under pressure.

2. Versatility:

Available in various types and sizes, flanges accommodate different pipe materials (such as steel, stainless steel, PVC) and configurations (weld neck, slip-on, socket weld, etc.), making them versatile for various application needs.

3. Sealing capability:

Flanges feature a sealing surface (often with a gasket) that ensures a tight and leak-free connection when properly installed. The flange surface must be even and flat to ensure a proper seal with the gasket. This capability is crucial in preventing fluid or gas leakage, maintaining system efficiency, and ensuring environmental safety.

4. Pressure and temperature resistance:

Flanges are manufactured from carbon steel, stainless steel, and alloy steel, selected based on the specific application’s pressure and temperature requirements. Raised face flanges are commonly used in high-pressure and high-temperature applications due to their enhanced sealing capabilities. This ensures they can withstand high pressures and extreme temperatures without compromising performance.

5. Ease of assembly and maintenance:

Flanges facilitate easy assembly and disassembly of piping systems, enabling quick maintenance or repairs. They also allow components to be connected or disconnected without needing to modify the entire system, saving time and cost.

6. Compatibility:

Flanges are designed to be compatible with standard dimensions and specifications (ANSI, ASME, DIN, etc.), ensuring interchangeability and ease of procurement for industrial projects globally.

7. Corrosion resistance:

Depending on the material used, flanges exhibit varying resistance to corrosion, chemicals, and environmental factors. This characteristic enhances their longevity and reliability in harsh operating conditions.

8. Standardization:

Flanges are manufactured according to international standards, which define dimensions, pressure ratings, and materials. This standardization ensures uniformity and compatibility across different manufacturers and applications.

How Do Flange Connections Work?

Flange work

Flange connections are the sturdy links that join pipes, valves, and equipment in various industries, such as plumbing and construction. They ensure secure and efficient fluid handling by creating robust seals between components.

A backing flange is often used in systems with limited space or requiring frequent disassembly and maintenance, providing additional support for lap joint flanges.

Flange connections create a secure and reliable seal between pipes, valves, pumps, and other equipment in a piping system. They consist of two flange ends bolted together with a gasket placed between them to ensure a leak-proof seal.

The flanges are typically matched to the size and pressure rating of the piping system, with bolts passing through holes in the flanges to tighten and secure the connection. The gasket material is chosen based on the specific application and the type of fluid being transported, ensuring compatibility and durability.

Common Types of Flanges: Weld Neck Flange

1. Socket-Weld Flanges:

Socket-Weld Flanges

The pipe is inserted into a socket end and welded on the outside.

Uses: It is typically used for small diameter, high-pressure pipes. It provides a smooth bore with added strength and is commonly found in chemical and power plants.

2. Lap Joint Flanges:

Lap Joint Flanges

Works with a stub end, with the flange slipping over the pipe and the stub end providing the sealing surface.

Uses: It is often used in systems requiring frequent dismantling for inspection and cleaning, such as in the food and pharmaceutical industries. It allows for easy alignment and flexibility.

3. Blind Flanges:

Blind Flanges

A bling flange has no bore and is used to close the end of a piping system or vessel opening.

Uses: Ideal for high-pressure applications where sealing the end of a pipe is necessary, often used in testing and maintenance operations.

4. Weld Neck Flanges:

Weld Neck Flanges

A weld neck features a long-tapered hub that provides reinforcement. A welding neck flange is designed to provide a stronger and more durable connection, commonly used in high-pressure and high-temperature applications.

Uses: Ideal for high-pressure and high-temperature applications, they are commonly used in the oil, gas, and petrochemical industries due to their ability to handle extreme conditions.

5. Slip-On Flanges:

Slip-On Flanges

Slip-on flanges slide over the pipe and are welded inside and outside.

Uses: These are suitable for lower-pressure applications. They are easier to install and align than weld neck flanges and are often used in water and gas lines.

6. Threaded Flange:

Threaded Flange

The threads inside the flange bore to match the pipe threads. Threaded flanges feature a threaded inner bore that matches the male thread on the pipe or fitting, providing a secure connection.

Uses: It is suitable for low-pressure systems and applications where welding is not feasible, such as in water and air services and particularly in hazardous areas.

7. Long Neck Welding Flanges:

Similar to weld neck flanges but with a longer neck.

Uses: Reinforces applications with high stress and long pipe lengths, often used in nuclear and thermal power plants.

8. Orifice Flanges:

These are used with orifice meters to measure the flow rate of liquids or gases.

Uses: It is commonly used in flow measurement and metering systems, often in industries such as oil and gas and chemical processing, to accurately measure and regulate flow rates.

9. Speciality Flanges:

Specialty flanges are designed for specific applications and requirements that standard flanges may not meet.

Flat Face (FF): Flat face flanges have an even, flat surface. Flat face flanges are vulnerable to damage during handling and transport, so flange covers are often used to protect them.

Uses: They are typically used in low-pressure applications where the flange is bolted to a flat surface, such as in water treatment and pump systems.

Different Face of a Flange to Connect: Raised Face Flanges

1. Raised Face (RF):

The sealing surface is raised above the bolt circle face. RF is Commonly used in various industries for high-pressure applications. The raised area helps concentrate the sealing pressure on the gasket, improving the seal.

2. Male and Female Face (M&F)

In MF, one flange has a raised (male) face, and the other has a matching recessed (female) face. This arrangement provides precise alignment and is used in systems where gasket containment is crucial. It is common in chemical processing and refinery applications.

3. Tongue and Groove (T&G)

In T & G, one flange has a raised ring (tongue), and the other has a matching groove. This connection ensures proper alignment and gasket placement, and it is often used in high-pressure and high-temperature applications. It also provides a reliable seal in pipeline systems.

4. Flat Face (FF)

The entire face of the flange is flat and in the same plane as the bolt circle face. FF is used in low-pressure applications where the gasket material can be easily compressed. It is commonly found in water treatment and pump systems.

5. Ring Joint Face (RTJ)

RTJ had a groove cut into its face to accept a metal ring gasket. This provides a high-integrity, leak-proof seal under high-pressure and high-temperature conditions. It is frequently used in oil and gas drilling and production operations.

6. Flange Classification

Flanges are classified based on pressure-temperature ratings, which determine their suitability for different service conditions. The most common classifications are based on standards set by organizations like ANSI (American National Standards Institute), ASME (American Society of Mechanical Engineers), and others.

Common Flange Classifications

ANSI/ASME B16.5: Class 150, Class 300, Class 400, Class 600, Class 900, Class 1500, Class 2500

These classes denote the maximum allowable pressure a flange can withstand at a given temperature. The higher the class, the greater the pressure rating.

Service Ratings

Pressure Ratings


Class 150

Approximately 270 PSI at room temperature.

Suitable for low-pressure applications such as water treatment plants and low-pressure steam systems.

Class 300

Approximately 740 PSI at room temperature.

Used in medium-pressure applications like air compressors and high-pressure water systems.

Class 600

Approximately 1480 PSI at room temperature.

Common in high-pressure steam, oil, and gas pipelines.

Class 900

Approximately 2220 PSI at room temperature.

Suitable for high-pressure applications in chemical and oil refineries.

Class 1500

Approximately 3705 PSI at room temperature.

Utilized in very high-pressure systems such as industrial chemical plants and power generation.

Class 2500

Approximately 6170 PSI at room temperature.

Designed for extremely high-pressure applications, often found in offshore drilling and high-pressure steam systems.


Material Mechanical testing is a series of testing methods used in analyzing products and materials to ensure safety during production, proper use of materials, and cost effectiveness. It is an important part of every design and manufacturing industry. This article provided many mechanical engineering tests and their importance in manufacturing.


Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.

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