Flanges Explained: What You Need to Know

Flanges Feature

Flanges are the second most popular joining method after welding, highlighting their crucial role in the vast world of manufacturing. They are celebrated for being among the easiest and most dependable methods used in applications worldwide. Today, it’s impossible to think of a drainage pipe or any valve being connected without the assistance of a flange.

Since their inception in 1809, flanges have significantly evolved and improved. Over the years, they have become indispensable in various sectors, including plumbing, boiler work, pressure vessels, and even in the cutting-edge field of nuclear fusion. In today’s article, we’re explaining everything you need to know about flanges. So, let’s start the exploration.


What is a Flange?

A flange is a mechanical component that links pipes, valves, pumps, and additional apparatus to create a cohesive piping network. This connection facilitates straightforward access for maintenance, inspection, or alterations. Typically, flanges are either welded or bolted onto these systems, ensuring a reliable union. A flange serves as a plate or ring that creates a rim at the end of a pipe, establishing a secure flange connection to the pipe when it is fastened in place.


How Does Flanges Work?

Flanges work by establishing a flange-to-flange connection, where two flanges are joined together with a gasket between them to ensure a tight seal. This seal is crucial for preventing leaks. Bolts are distributed and tightened evenly across the flange, further securing the connection. This method strengthens the pipe but also facilitates easy assembly and disassembly of piping systems.

The functionality and efficiency of flanges significantly depend on their manufacturing method; for instance, cast flanges excel in complex shapes and sizes, offering versatility for specialized configurations but may have variability in the microstructure. Welded flanges, created by joining metal pieces using high heat, provide superior strength and are ideal for high pressure. Forged flanges, made by shaping metal under high pressure, boast exceptional durability and uniformity.


7 Popular Types of Flanges

Your piping system is a vital component of any residential, commercial, or industrial infrastructure, acting as the lifeline that promises the seamless flow of fluids or gases. Choosing the right type of flange is a must, as an ill-suited flange can lead to fragile connections, resulting in leaks, system malfunctions, and the potential for costly, recurring repairs. To avoid these pitfalls, it’s essential to familiarize yourself with the basic kinds of flanges available on the market. Here, we have listed the best types of flanges with pictures:

1. Weld Neck Flange

Weld Neck Flanges are distinguished by their long tapered hub, which gradually transitions from the thickness of the pipe to the flange’s thickness, providing inherent reinforcement and stability. This design allows for the distribution of stress between the flange and the pipe, making it ideal for high-pressure and high-temperature applications. Weld Neck Flanges come in various sizes and weights, typically ranging from 1/2 inch to 24 inches in nominal pipe size (NPS), with pressure ratings from 150 to 2500 pounds.

Weld Neck Flange


  • Power plants and petrochemical industries.
  • Steam lines heat exchangers.
  • Cryogenic services, refrigeration.


  • High-pressure tolerance.
  • Minimized fluid turbulence.


  • Higher cost.
  • Complex installation.


2. Long Welding Neck Flange

It’s evident from the name that this flange type has a very long neck that acts as a bore extension. Long welding neck flanges are also known as straight hub welding flanges or heavy barrel flanges. The average size and weight of a Long Weld Neck (LWN) flange depend on the pressure class, the nominal pipe size, and the flange thickness.

Long Welding Neck Flange


  • Storage tanks and reactors.
  • Distillation columns and absorbers.
  • Drum sections of boilers and towers.


  • Improved stress distribution.
  • Enhanced piping alignment.


  • Increased weight.
  • Higher material cost.


3. Slip-on Flange

Slip-on Flanges are characterized by their ease of installation, as they simply slip over the end of a pipe and are then welded in place. This design allows for a somewhat easier alignment compared to weld neck flanges. They are mostly suitable for lower-pressure and temperature applications.

Slip on Flange


  • Water distribution systems.
  • HVAC and fire protection.
  • Low-pressure industrial processes.


  • Simplified pipe alignment.
  • Cost-effective solution.


  • Lower pressure limits.
  • Required two welds.


4. Socket Weld Flange

Socket Weld Flanges feature a recessed area that allows the pipe to sit inside the flange before welding, creating a smooth and stable connection. This design is particularly effective for smaller-diameter piping systems where high pressure is a concern. Socket Weld Flanges are available in different sizes. For example, the flange of pressure class 150 and nominal pipe size 2 inches has a flange thickness of 14.2 mm and a flange weight of 1.8 kg.

Socket Weld Flange


  • Steam conduits and high-pressure oil lines.
  • Some aerospace systems.
  • Hydraulic systems.


  • Strong, leak-proof connection.
  • Ideal for small pipe diameters.


  • Prone to crevice corrosion.
  • Complex installation process.


5. Lap Joint Flange

Lap Joint Flanges are designed for use with stub ends, allowing for easy disassembly and assembly of piping systems. This type of flange consists of two components: the flange itself, which is freely rotating, and the stub end, which is directly welded to the pipe. Lap Joint Flanges are particularly advantageous in systems requiring frequent dismantling for inspection and cleaning. They are compatible with a wide range of pipe diameters, accommodating various industrial needs without specifying exact size ranges.

Lap joint flange


  • Piping systems require regular maintenance.
  • Corrosive fluid handling.


  • Facilitates easy pipe inspection.
  • Simplifies pipe alignment.


  • Requires stub end for installation.
  • Not suitable for high-pressure applications.


6. Threaded Flange

Threaded Flanges are uniquely designed to be screwed directly onto the pipe without the need for welding. This feature significantly simplifies installation and maintenance, especially in explosive, flammable, or hazardous environments where welding poses a safety risk. Threaded flanges are suitable for various pipe sizes, adapting seamlessly to different industrial settings by offering a straightforward solution for connecting pipes.

Threaded Flange


  • Hazardous fluid transport.
  • Systems where welding is impractical.
  • Quick assembly and disassembly required areas.


  • Eliminates welding requirements.
  • Easy to install and maintain.


  • Limited to low-pressure applications.
  • Risk of leakage under fluctuating pressure conditions.


7. Weldo Flange/Nipo Flange

Weldo/Nipoflanges combines the functionality of weld neck flanges with the convenience of a welding outlet or nipple, creating a versatile and efficient means of making branch connections in piping systems. These specialized flanges are directly welded onto the pipe, providing a strong and compact connection point for branching off to instruments, valves, or other pipes.

Weldo Flange


  • Instrumentation and control systems.
  • Auxiliary piping connections in process industries.
  • High-pressure and high-temperature environments.


  • Compact and efficient design.
  • Facilitates direct branching from main pipes.


  • More complex to install than standard fittings.
  • Limited flexibility once installed.


Connection Face of Flanges

The connection face of a flange is known as a feature that determines how it seals and mates with another flange in a piping system. This face can be designed in various forms, each tailored to meet specific sealing requirements and pressure ratings. Here are some of the most common types of flange faces:

  • Flat Face (FF): Flat face flanges feature a flat surface extending from the bolting circle to the center hole, suitable for low-pressure applications where the mating flange or gasket has a flat surface.
  • Raised Face (RF): Raised face flanges have a raised area around the bore, improving the concentration of compressive force on the gasket.
  • Ring-Type Joint (RTJ): RTJ flanges are designed with a groove cut into their face to accommodate a metal ring gasket, ideal for high-pressure and high-temperature applications requiring a robust seal.
  • Tongue and Groove (T&G): Tongue and groove flanges consist of a matching pair where one flange has a raised ring (tongue) that fits into a groove on the mating flange, providing excellent fluid-tightness in moderate-pressure systems without the need for a gasket.
  • Male and Female (M&F): Male and female flanges include a protruding male face and a matching recessed female face, enhancing alignment and sealing capability.

Connection Face of Flanges


Understanding Flange Dimensions for Optimal Compatibility

The selection of the appropriate type of flange in piping is the initial step in ensuring the integrity and functionality of your piping system. However, understanding flange dimensions is equally important for achieving optimal compatibility. So, here are some essential flange dimensions to consider,

  • Nominal Pipe Size (NPS) or Bore: This is essentially the inside diameter of the flange and the pipe it connects to. It determines how big the opening is.
  • Outside Diameter (OD) of the Flange: Think of this as the flange’s total width from one edge to the other. It’s the largest part you’ll measure across the flange face.
  • Thickness (Tf) of the Flange: This measures how thick the flange is from the front where it meets the pipe to the back. A thicker flange can often handle more pressure.
  • Diameter of the Raised Face: The raised face is a small portion that sticks out around the flange’s center hole. Its diameter is crucial for ensuring the gasket fits snugly for a tight seal.
  • Length Through the Hub (X): This dimension measures how long the flange extends from the front face to the end of the hub.


Materials Used In Making Flanges

Until now, you must have grasped the idea that flanges are often regarded as the lifelines of various piping systems. That’s the reason the choice of flange material used in manufacturing cannot be overstated. So, here’s an overview of the primary materials used in flange manufacturing in a comprehensive table:

Materials Usage Advantages
Carbon Steel Oil and gas pipelines, heating systems, manufacturing processes Durability, performance, cost-effectiveness, withstand high stress and shock
Stainless Steel Chemical processing, food and beverage production, maritime operations Corrosion and oxidation resistance, strength at high temperatures
Alloy Steel Power plants, chemical plants, refineries Improved hardness, increased strength, resistance to wear and corrosion
Aluminum Aerospace, automotive, and chemical processing environments Lightweight, natural corrosion resistance, excellent thermal and electrical conductivity


Manufacturing Process of Flanges

Above, we have explained all of the materials that can be used in making flanges, and that is the initial step in the manufacturing of flanges. After selecting the appropriate material, there are three main steps in the production process to transform these materials into functional flanges.

Step 1: Cutting and Shaping

The first major step involves cutting and shaping the selected material into the basic form of a flange. This process starts with cutting a circular disc from the chosen material, which then undergoes shaping to create the preliminary outline of the flange. Advanced cutting technologies such as laser cutting, waterjet cutting, or traditional mechanical methods are employed to ensure precision and efficiency.

Step 2: Forging and Welding

Following the initial shaping, the flange material undergoes forging and, in some cases, welding. The process of forging involves heating the material to a high temperature and then applying force to mold it into the specific flange shape, enhancing its mechanical properties by refining its grain structure. Certain flange types, like steel flanges, require welding to attach additional components or to reinforce the structure.

Step 3: Machining and Surface Finishing

This is the final step in the manufacturing process of flanges. Machining refines the flange to its precise specifications, including drilling bolt holes, finishing the flange face for a smooth seal, and creating the bore to match the pipe’s diameter. CNC machines offer high precision in this phase. Surface finishing enhances the flange’s resistance to corrosion and wear.



This guide has got everything you need to know about flanges, from different types of flanges to their manufacturing process and everything in between. Here at JIAHUI, we’ve been making flanges in all types of shapes, sizes, and materials for decades. So, if you’re looking for top-notch flanges that fit just right for your project, you’re in the right place. We’re all about making sure you get exactly what you need, with a touch of that JIAHUI quality and care.

Leave a Reply

Your email address will not be published. Required fields are marked *

Extensive Industry Knowledge
Related Blogs

Precision is key in advanced manufacturing. Honing is an intricate machining process that has
Read more

Case hardening, an essential metallurgical process, transforms metal components and their functionality across industries
Read more

Screen printing stands out for its wide-ranging application across industries - fashion and advertising.
Read more

Request A Quote

Do you need our services? Contact us now by phone, email or through our contact form.

Sign Up For Our Newsletters

You cannot copy content of this page