Basic Knowledge of Flange

The flange is a ring-shaped device that can be used instead of welding or threading various piping system components used throughout the piping system. Because they may be easily dismantled for transportation, routine inspection, maintenance, or replacement, flanged connections are used as an alternative to welding. Because threading large bore pipe is neither cheap nor dependable, flange ends are preferred. The flange is an essential part of every plumbing system.

Flanges are most commonly employed when connecting or disassembling a junction is required. Flanges can be found in pipe-to-fitting joints, valves, equipment, or any other important component of the piping system.

Flange Parts

A typical flanged connection is comprised of three parts:
  • Pipe
  • Flanges
  • Gasket
  • Bolting

Common Flange Types and Characteristics

Flanges are not a one-size-fits-all answer. Aside from sizing, selecting the best flange design for your piping system and intended use will help to assure dependable performance, a long service life, and a competitive price.

Here are some of the most prevalent flange types:

Threaded Flange

Threaded Flange
Threaded Flange

This design, also known as a screwed flange, has a thread inside the flange bore that matches the matching male thread on the pipe or fitting. Because of the threaded connection, you may avoid welding in many applications. Simply match the threading to the pipes to be joined.

Socket-Weld Flange

Socket Weld Flange
Socket-Weld Flange

Socket-weld flanges have a connection in which you fit the pipe into the flange and then secure the connection with a single multi-pass fillet weld. This makes this form easier to install than other welded flange types while eliminating the drawbacks of threaded ends.

Slip-On Flange

Slip On Flange
Slip-On Flange​

Slip-on flanges are widely used and come in a variety of sizes to support systems with increased flow rates and throughput. Installation is a little more complicated because you’ll need to fillet-weld both sides of the flange to fasten it to the pipe.

Lap Joint Flange

Lap Joint Flange
Lap Joint Flange

Lap joint flanges are two-piece designs that require butt welding the stub end to the pipe or fitting and the use of a backing flange to produce the flanged connection. Because of this, this type is ideal for usage in systems with limited physical area or systems that require frequent disassembly and repair.

Weld Neck Flange

Weld Neck Flange
Weld Neck Flange

Weld neck flanges require butt welding for installation. Their integrity, performance in systems with multiple repeat bends, and ability to be used in high-pressure and high-temperature systems, on the other hand, make them a top choice for process piping.

Blind Flange

Blind Flange
Blind Flange

Blind flanges are simply boltable blank discs that are used to terminate or isolate pipe systems. When properly placed and combined with the appropriate gaskets, they can provide an excellent seal that is simple to remove when necessary.

Specialty Flange

Specialty Flange
Nipple Flange
Specialty Flange
Orifice Flange
Long Weld Neck Flange
Long Weld Neck Flange

Nipple flanges, an essential component of fluid conveyance systems, securely join pipes and fittings. These threaded extensions are short and offer leak-free couplings and ease of installation. Nipple flanges, known for their adaptability, play an important part in a variety of sectors, from plumbing to oil and gas, guaranteeing efficient fluid movement.


Orifice flanges are critical components of fluid measuring and control systems. They have a precision-drilled hole that allows for accurate flow rate and pressure monitoring. These flanges are widely used in industries such as petrochemicals and manufacturing, where they ensure accurate fluid management and efficient processes.


Long weld neck flanges are designed for important applications requiring strength and integrity. Their expanded neck design provides additional support, decreasing joint stress. These flanges are extensively used in industries such as oil & gas and power generation and are ideal for high-pressure systems.

Flange Facing Types

    • Flat Face (FF): As the name implies, flat face flanges have a flat, even surface with a full face gasket that contacts the majority of the flange surface.
    • Raised Face (RF): These flanges have a little elevated area around the bore and an inside bore circle gasket.
    • Ring Joint Face (RTJ): This face type is used in high-pressure and high-temperature procedures and has a groove in which a metal gasket sits to maintain the seal.
    • T&G (Tongue-and-Groove): These flanges have matching grooves and elevated portions. The design facilitates installation by allowing the flanges to self-align and providing a reservoir for gasket glue.
    • Male and female (M&F) flanges: These flanges, like tongue and groove flanges, use a matching pair of grooves and raised parts to hold the gasket. Unlike tongue and groove flanges, however, these keep the gasket on the female face, allowing for more accurate positioning and a wider range of gasket material alternatives.

Flange Dimensions

Apart from a flange’s functional design, flange dimensions are the most probable factor to influence flange selection when developing, maintaining, or updating a pipe system. To ensure adequate sizing, consider how the flange interfaces with the pipe and the gaskets in use.

Common factors to consider include:

    • Outside diameter: The distance between two opposing flange face edges.
    • Thickness: The thickness of the outer adhering rim.
    • Bolt circular size: The distance calculated from center to center between opposing bolt holes
    • Pipe size: A reference to the pipe size to which the flange relates.
    • Nominal bore size: The inner diameter of the flange connector.

Flange Classification and Service Ratings

Flanges are frequently classified according to their capacity to tolerate high temperatures and pressures. This is denoted by a number followed by the “#,” “lb,” or “class” suffix. These suffixes are interchangeable, but they will vary depending on the location or provider.

Typical classifications include:

  • 150#
  • 300#
  • 600#
  • 900#
  • 1500#
  • 2500#

The exact pressure and temperature tolerances will vary depending on the materials utilized, the flange design, and the flange size. The sole constant is that pressure ratings decline as temperatures rise in all circumstances.

Flange Standards and Markings

blog flange label
Typical flange markings can be found on a flange

Flanges are classified as global standards created by the American Society of Mechanical Engineers (ASME) – ASME B16.5 & B16.47.

To aid in the replacement or verification of existing parts, all flanges must carry markings – often on their outer perimeter.

These markers are also in a certain order:

  • Logo or code of the manufacturer
  • ASTM material code
  • Material Grade
  • Service rating (Pressure-temperature Class)
  • Dimensions
  • Thickness (Schedule)
  • Special designations, if applicable — for example, QT for quenched and tempered or W for welding repair

Looking for flanges, fittings, pipes, valves and gasket?

Saliran Group has over 10 years of experiences in trading of a wide range of flanges, pipes, valves, fittings, gasket and related parts and accessories (“PVF products”) as well as steel products with numerous happy customers all around the world. We supply a variety of gaskets either in metal, non-metal as well as food-grade approval available material.

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