What is A Flange: Types, Connection, and Machining Process

what is a flange

Flanges are important components of most mechanical systems. They offer a mechanical means of joining or assembling parts such as pipes, fittings, and valves. Besides, they can also be disassembled when used, making them ideal for use with systems that would require maintenance.

So, what is a flange? What are the types of flanges? What are the considerations when designing flanges? Read on we will provide information to help you make the right manufacturing decisions.

What is a Flange?

Flanges, meaning rims, are symmetrical disc-like components that are used to attach or seal pipes, containers, or fixed-shaft mechanical pieces. These disc-shaped components are most frequently found in plumbing and are typically used in pairs. There are also different types of fasteners and threaded fixings are used to secure the flanges in place.

In addition, a flange features bolt holes. Two flanges are normally joined to pipe ends with a gasket in between, and the connection between them is made with bolts.

flange components

Characteristics of Flanges

  • Flanges have accurately drilled holes for easy assembly.
  • They have controlled grain flow for optimal strength and stiffness.
  • To facilitate good welding, flanges are machined bevels.
  • For unrestricted flow when used for piping system, flanges are smooth and have accurate bore.
  • This component has spot-facing to ensure fastener seating stays true and square.

How Does Flange Connection Work?

flange connection

A flange connection is an assembly involving two pieces of equipment, pipes or pipe fittings, two flanges, flange mats, and bolts. Different types of washers are also used with the flange connection to secure the connection.

Besides, a flange connection culminates in joining two materials using inner and outer lip parts or flanges. For each of the opposing flange faces to form a seal, force (gasket compression or sealing pressure) must be exerted and maintained. To ensure flanges stay in place, they are often bolted with a gasket between the flange faces to form a tight seal. One of the gaskets often used for this sealing is a disk spring, which is a type of spring.

Common Types of Flanges and Their Uses

flanges types

Choosing the right flange for your piping system or intended joining purpose will help to guarantee dependable performance, a long service life, and affordable cost. Below are common flange types and their uses.

Socket-Weld Flanges

Socket-weld flanges have a connection where you insert the pipe into the flange, similar to snap-fit joints. A multi-pass filet weld helps secure the connection. This makes socket-weld flanges ideal for smaller pipe diameters in low-temperature and low-pressure conditions. Therefore, These flanges eliminate the constraints of threaded ends and make this form easier to set up than other welded flanges.

lap joint flanges

Lap Joint Flanges

Lap flange joints have a two-piece construction, and the flanged connection is made by welding the shaft end to the pipe or fitting and using a backing flange. Because of its design, this form is well-liked for usage in systems with constrained dimensions or requiring frequent disassembly and maintenance.

Blind Flanges

Blind flanges, simply blank discs that are easy to bolt, find use in the isolation or termination of piping systems. When placed correctly and used with the appropriate gaskets, they can create an excellent seal that is simple to remove when necessary.

Weld Neck Flanges

Weld neck flanges need to be shaft welded to be installed, just like lap flange joints. However, their reliability makes them a popular option for process pipes. They also perform excellently in systems with several repeat bends, making them ideal for high-temperature and pressure systems.

Slip-On Flanges

Slip-on flanges are widely used and come in various sizes to support systems with increased flow rates and throughout. All you need to do is match the pipe’s outer diameter to the flange. The flange must be securely fastened to the pipe on both sides, which makes installation a little more technical.

Threaded Flanges

This design, also called a flange screw, features a thread inside the flange bore that matches the male thread on the pipe or fitting. You may dispense with welding in many applications thanks to the threaded connection. To use threaded flanges, matching the thread to the pipes you want to connect is best.

long neck welding flange

Long Neck Welding Flanges

Long weld neck flanges, also known as integral flanges, indicate that the neck of a welding neck flange is extremely lengthy. The welding neck flange commonly features a conical neck and a bevel end butted together with the complementary pipe.

Orifice Flanges

When orifice plates or flow nozzles are utilized, orifice flanges are used instead of the typical pipe flanges. This mainly aims to gauge how quickly gases or liquids are moving through the appropriate pipeline.

Special Flange Types You Need to Know

Special flanges are flange types that are suitable for use in a diverse range of environments. They also include flange types with a diverse range of uses. Special flange types include:

  • Expanding flanges
  • Nipo Flanges
  • Reducing flanges
  • High hub flanges
  • Ring type flanges
  • Groove and tongue flanges
  • Loose flanges
  • Spectacle blind flanges

Different Face of A Flange to Connect

Face type is an important concept to consider when choosing flanges. The reason is that the type of face a flange has determines the type of gasket needed to install it and the type of seal it would create.

flange face

Below are the different faces of a flange.

Raised Face (RF)

These flanges have an inner bore circle gasket and a tiny elevated portion around the bore. There are raised face flanges for various pressure and temperature ratings. Also, the most prevalent form of flange used in the oil and gas and chemical engineering sectors is RF flanges.

Male and Female Face (M&F)

To hold the gasket in place, these flanges have elevated parts and matching grooves. However, gasket retention happens on the female face, offering more precise positioning and a wider range of materials.

Tongue and Groove (T&G)

The grooves and raised areas on these flanges mirror those on the male and female face flanges. This facilitates installation because the design encourages self-alignment of the flanges and creates a reservoir for gasket glue.

Flat Face

As their name implies, flat face flanges have an even, flat surface. They also have a full-face gasket covering most of the flange surface.

Ring Joint Face (RTJ)

This face type, used in high-pressure and temperature applications, has a notch in which a metal gasket is placed to maintain the seal.

Flange Dimensions and Considerations for Ensuring the Right Sizes

Flanges are most likely influenced by flange size when developing, maintaining, or enhancing a piping system. To ensure the flange is sized correctly, you must consider how it connects to the pipe and the gaskets being used. Here are some considerations when choosing flange dimensions.

  • Thickness: When choosing a flange, it is best to consider thickness—the thickness of the outer attaching rim.
  • Normal bore size: This measures the inner diameter of the flange connectors
  • Bolt circle diameter: When measured from center to center, this is the distance between bolt holes on opposite sides.
  • Pipe size: A pipe size ideal for the flange being used.

Below are tables showing flange dimensions.

class 150 flange dimension chart

class 300 flange dimension chart

class 400 flange dimension chart

class 600 flange dimension chart

Flange Standards and Markings

Flange designs are governed by the international standards ASME B16.5 & B16.47, which facilitate comparison. These standards were developed by the American Society of Mechanical Engineers (ASME).

All flanges must have markers to aid in replacing or verifying existing parts. Typically, these markers are located on the outer perimeter of the flange.

flange markings

These indicators also adhere to a rigid hierarchy:

  • Logo or code for the manufacturer
  • ASTM code of materials
  • Material quality
  • Pressure-temperature class service rating
  • Size
  • The thickness (Timeline)
  • Heat index
  • Bore
  • Any special identifiers, such as QT for quenched and tempered or W for welding repair

Machining Process of Flange Parts

Several stages are involved in the flange part machining process, ranging from material selection to surface finish. Below is the machining process for making high-quality flanges.

stainless steel flanges

Material Selection

Picking the right flange materials is the first stage in the machining process. The most popular materials for making flanges are alloy steel, carbon steel, or stainless steel. However, the ideal material often depends on the application’s temperature, pressure, and corrosion resistance needs.

Material Cutting and Shaping

Following selection, the material is sliced and formed. Big metal plates are cut into smaller pieces to get the right size for the flange. The produced parts are then heated to the proper temperature to prepare them for further processing.

Heat Treatment

Depending on the material and purpose of a flange, the flanges may undergo heat treatment methods such as annealing, quenching, or tempering. Heat treatment boosts the flange’s mechanical properties while enhancing its resilience, toughness, and resistance to wear and corrosion.

Forming and Forging

The heating process makes the metal components malleable, facilitating the proper flange shape development. Machinists utilize different methods to forge the flange, including hot forging and cold forging. The metal is formed at room temperature in cold forging, while hot forging involves forming heated material/metal under high pressure.

machining flange


After the initial cutting and shaping, the flange is machined to achieve precise tolerances and to refine its dimensions. This operation includes facing sealing surfaces, chamfering edges, and drilling holes for bolt connections. CNC (Computer Numerical Control) machines are often used for automated and precision machining.

Surface Finish

Flanges might undergo surface finishing operations like grinding or polishing to achieve the desired smoothness, remove surface defects, and improve their overall look.

Inspection and Quality Control

Quality control is an important stage in the production of flanges. Flanges undergo a thorough examination process to ensure they comply with the appropriate norms and specifications. Inspecting for quality control includes measurement inspections, finishes and surface analyses, and non-destructive testing methods like ultrasound or magnetic particle analysis.


Manufacturing or machining of flanges involves several processes to get the best quality. There are also standards that govern its production as well as markings that help for verification in case of replacement or manufacturing. Besides, there are different types of this component and they all have their specific and special uses.

WayKen is a professional manufacturing company focusing on machining prototypes and parts, including flanges and other components for fasteners. We maintain a high standard to provide many sectors with high-quality machining services at affordable costs. Our team and engineers are constantly available to receive your order and process it as quickly as possible, decreasing market time.


What materials are ideal for making flanges?

Common materials for making flanges include carbon steel, cast iron, nickel alloy, stainless steel, bronze, brass, and aluminum.

What are the specifications of flanges?

Standard flanges are covered by the ASME B16.5 and ASME B16.47 specifications, while European steel flanges are covered by the EN 1092-1 specification.

When is it best to use a flange fitting?

In high-pressure situations, larger flange connections make assembly simpler than utilizing too many large fittings. The flange fittings also include a zero-clearance arrangement, making it simple to disconnect and rejoin them in order to maintain manifold, tube, and hose connections.

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