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Flanges: Types, Machining Process, Materials, Application

Table of Contents

Flanges are a cornerstone component in intricate piping systems, connecting a symphony of pipes, valves, and pumps. These crucial elements, available in many types and materials, ensure a seamless and secure flow within various industrial applications.

This article delves into the diverse types of flanges, their meticulous machining processes, the robust materials they are forged from, and the broad spectrum of their applications while navigating the standards governing their use. Join us as we unlock the complexities behind the pivotal role that flanges play in the integrity and efficiency of modern piping systems.

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What is a flange?

Flanges are important piping components often used to connect two pipes, valves, pumps, or other equipment so that they can form a continuous fluid transfer system.

A flange usually consists of a round, flat component with one or more holes for receiving bolts or other fasteners to connect two-facing flange surfaces. Flanges can be cast, threaded, or welded.

Flange characteristics

1.Various connection methods

Flanges can be connected by welding, bolts, or screws, and are suitable for a variety of different piping systems.

2.Easy to install

The design of the flange makes pipe connection simple and convenient, easy to install and maintain.

3.Good sealing

With the corresponding sealing ring or gasket, the flange can achieve a good sealing effect and prevent media leakage.

4.Various structure types

Flanges include flat welding flanges, butt welding flanges, socket welding flanges, threaded flanges, blind flanges, and other types, which are suitable for different pressure levels and usage occasions.

5.Wide choice of materials

Flanges can be made of carbon steel, stainless steel, alloy steel, copper, aluminium, and other materials to adapt to different media and environments.

6.Standardized production

The production and design of flanges usually follow international or national standards, such as ANSI, DIN, JIS, etc., ensuring product interchangeability and reliability.

7.Precision Machining for Alignment

All faces of the flange are machined within strict tolerances, ensuring true alignment and a reliable connection in the overall assembly.

Types of Flanges

Delving deeper into the realm of flanges, it becomes apparent that the variety of flange types is as diverse as the applications they serve. Each type is designed with unique characteristics to ensure flanges fit perfectly within a specific piping system.

Common Types of Pipe Flanges:

  • Weld Neck Flanges
  • Slip-On Flanges
  • Blind Flanges
  • Threaded Flanges
  • Socket Weld Flanges
  • Lap Joint Flanges
  • Plate Flanges

Weld Neck Flanges

Recognised by their protruding necks, these flanges are welded to the base of the pipe, providing a robust and durable connection. The weld neck design is ideal for handling high-pressure applications, as it can effectively distribute stress across the connected elements.

Slip-On Flanges


These flanges are slipped over the pipe and then welded into place. They are more economical than weld neck flanges and are used commonly in lower-pressure environments.

Blind Flanges

Blind Flanges

Unique among flange types, blind flanges are used to seal the end of piping systems, valves, or pressure vessel openings. They are essential for performing maintenance or repairs in a piping system.

Threaded Flanges

Threaded Flanges

Threaded or screwed flanges are connected to pipes without welding, which is advantageous in scenarios where hot work (like welding) is not possible. These flanges are suitable for low-pressure applications and are not recommended when severe bending stresses are present.

Socket Weld Flanges

Socket Weld Flanges

Designed for smaller-sized high-pressure pipes, these flanges allow the pipe to be inserted into the flange socket before welding. They offer an excellent flow characteristic and are less prone to leakage than others.

Lap Joint Flanges

Lap Joint Flanges

Used with stub ends, these flanges are ideal for systems that require regular dismantling for inspection and cleaning. They are beneficial in situations where the ability to rotate flanges and align bolt holes materially simplifies the assembly of the piping components.

Plate Flanges

Plate Flanges

Plate flanges are flat, circular discs welded onto the end of a pipe, used for making bolted connections between pipes in a piping system.

Flange Facing Types

Flat Face (FF) Flanges

With a flat surface that makes contact with the gasket, these are typically utilized in low-pressure, non-critical applications, where the sealing surface does not require compression.

Raised Face (RF) Flanges

The most common facing type, RF flanges, feature a raised surface that allows for a better seal with various gasket designs. They are versatile and can be used in a range of pressures.

Ring-Type Joint (RTJ) Flanges

Known for their grooved sealing mechanism, RTJ flanges are deployed in high-pressure and high-temperature applications, ensuring a strong and reliable seal.

Tongue and Groove (T&G) Flanges

These flange types utilize matching grooves and projections on the facing surfaces to create a tight, non-leaking seal. They are well-suited for applications that require a high level of seal integrity.

Flange Assembly

1. The flange surface, especially the sealing surface, must be cleaned before assembling.

2. When assembling the flat plate welding flange, insert the pipe end into the inner diameter 2≤3, then insert the pipe end into the flange. Spot welding of flange and pipe. If it is a horizontal pipe, the flange should be spot welded from above and then used with a 90° angle ruler to check and correct the flange position from different directions so that the sealing surface is perpendicular to the pipe. The centre line and the second point under the spot weld are correct.

3. Use a 90° angle ruler to check and correct the flange position from the left and right directions after passing the third point and the fourth point spot welding; complete the spot welding and fixing of the flange.

4.  Regarding the assembly of flange pairs, the bolt holes of the mounting flange should be consistent with the corresponding bolt holes of the fixed flange. Aligned and parallel to the fixed flange with a deviation of not less than 1.5% of the outer diameter per thousand flanges and not larger than 2mm.

5. When selecting matching flanges for equipment or valve components, attention should be paid to the legal requirements of the original equipment or valve components and whether the flange is consistent with the flange connection size used in the pipeline.

Machining Process of Flanges Parts

The machining process of flanges, crucial for their functionality in piping systems, involves transforming steel or stainless steel into precise components for a perfect fit. The process includes:

  1. Material Selection: Choosing stainless or carbon steel based on flange use.
  2. Cutting: Employing plasma, water jet, or sawing methods to cut material into disc-shaped blanks.
  3. Facing and Boring: Creating a flat surface on the blank and boring an opening to match the pipe’s internal diameter.
  4. Drilling: Precision drilling for bolt holes is essential for proper alignment with other piping components.
  5. Machining Flange Faces: Conducting operations based on the flange face type, ranging from simple to complex machining for specific surface features.
  6. Grooving and Serrating: Machining grooves or serrations for gasket sealing, adhering to industry standards.
  7. Finishing: Grinding and polishing the flange to eliminate machining marks and achieve the required smoothness.
  8. Inspection and Testing: Performing rigorous quality checks to ensure compliance with specifications for dimensions, material properties, and surface finish.

Applications of Flanges Across Industries

  • Oil and Gas
  • Chemical Processing
  • Water Treatment Plant
  • Power Generation
  • Pharmaceuticals
  • Food and Beverage Production
  • Shipbuilding and Marine
  • Construction and HVAC
  • Mining

Flange Standards

Flange standards are essential to ensure uniformity, safety, and interoperability of flange usage worldwide.

Overview of International Standards Governing Flange Dimensions and Use:

ASME B16.5 & B16.47

In the United States, the American Society of Mechanical Engineers (ASME) standards B16.5 and B16.47 outline specifications for flanges up to 60 inches in diameter.

ISO Standards

The International Organization for Standardization provides guidelines on dimensions and the quality of flanges through ISO 7005-1, among others, facilitating global trade and consistency.

DIN Standards

Germany’s DIN standards, including the popular DIN EN 1092-1, govern flange dimensions and are widely used in Europe and beyond.

BS Standards

The British Standards Institution (BSI), with standards like BS EN 1092-1, mirrors many DIN and ISO flange specifications, ensuring compatibility across regions.

JIS Standards

The Japanese Industrial Standards, like JIS B 2220, provide dimensions for flanges used within Japan and in specific international markets within Asia.

Flange Markings

Flanges typically carry markings to ensure correct usage and compliance with specific standards. The marking on flanges generally follows these principles:

  • Manufacturer’s Mark
  • Most flanges bear the manufacturer’s mark or name, which helps identify the producer and trace the product’s origin.
  • Material Specification
  • The type of material used, such as stainless steel, carbon steel, etc., is indicated on the flange. This helps determine the suitability of the flange for specific environments and conditions.
  • Pressure Rating
  • The flange displays its applicable pressure rating, like 150 lbs, 300 lbs, etc. This is determined based on standards like ANSI/ASME B16.5 or other relevant norms.
  • Dimensional Information
  • Includes the flange’s size, diameter, and thickness, among other details, to ensure compatibility with other piping system components.
  • Standard Certification
  • Flanges may carry marks indicating compliance with specific international or regional standards, such as ISO, ANSI, DIN, etc.
  • Batch Number and Date
  • The production batch number and manufacturing date help track the product’s production history and shelf life.
  • Other Special Markings
  • Depending on the requirement, flanges may also have additional unique markings, such as those for specific applications or environments.

Start A Flange Project Today

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1. What is the definition of a flange pipe?

A flanged pipe has a flanged end used for assembling dismountable connections.

2. What is a flange and its types?

A flange is a connector used to join pipe sections or fittings; types include welded neck, slip-on, blind, threaded, and lap joint.

3. Why are stainless steel flanges preferred?

Stainless steel flanges are preferred for their corrosion resistance, durability, and hygiene in various environments.

4. What are the different standards for carbon steel flanges?

Carbon steel flanges adhere to standards like ANSI/ASME B16.5, ASTM A105, DIN, and ISO.

5. What is an industrial flange?

An industrial flange is a mechanical component that connects pipes, valves, or equipment in industrial piping systems for assembly and maintenance.

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