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December 2, 2022

Commonly 6 Types of Flanges and What Information Do You Need When Selecting a Flange?

A flange is a method of connecting pipes, valves, pumps and other equipment to form a piping system. It also provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed. Flanged joints are made by bolting together two flanges with a gasket between them to provide a seal.

The Most Used 6 Types of Flanges:

  • Welding Neck Flange
  • Slip On Flange
  • Socket Weld Flange
  • Lap Joint Flange
  • Threaded Flange
  • Blind Flange

6 types flanges

Welding Neck Flange

Welding Neck Flanges are easy to recognize at the long tapered hub, which goes gradually over to the wall thickness from a pipe or fitting.
The long tapered hub provides an important reinforcement for use in several applications involving high pressure, sub-zero, and/or elevated temperatures.
These flanges are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion.
This flange type will be welded to a pipe or fitting with a single full penetration, V weld (Butt weld).

Slip On Flange

The calculated strength from a Slip On flange under internal pressure is of the order of two-thirds that of welding neck flanges, and their life under fatigue is about one-third that of the latter.
The connection with the pipe is done with 2 fillet welds, as well at the outside as also at the inside of the flange.
A disadvantage of the flange is, that principle always firstly a pipe must be welded and then just a fitting. A combination of flange and elbow or flange and tee is not possible, because named fittings have not a straight end, that complete slid in the Slip On flange.

Socket Weld Flange

Socket Weld flanges were initially developed for use on small-size high pressure piping. Their static strength is equal to Slip On flanges, but their fatigue strength 50% greater than double-welded Slip On flanges.
The connection with the pipe is done with 1 fillet weld, at the outside of the flange. But before welding, a space must be created between flange or fitting and pipe.
The purpose for the bottoming clearance in a socket weld is usually to reduce the residual stress at the root of the weld that could occur during solidification of the weld metal. The image shows you the X measure for the expansion gap.

Lap Joint Flange

Lap Joint Flanges have all the same common dimensions as any other flange named on this page however it does not have a raised face, they used in conjunction with a "Lap Joint Stub End".
These flanges are nearly identical to a Slip On flange with the exception of a radius at the intersection of the flange face and the bore to accommodate the flanged portion of the stub end.
Their pressure-holding ability is little, if any, better than that of Slip On flanges and the fatigue life for the assembly is only one tenth that of welding neck flanges.
They may be used at all pressures and are available in a full size range. These flanges slip over the pipe, and are not welded or otherwise fastened to it. Bolting pressure is transmitted to the gasket by the pressure of the flange against the back of the pipe lap (Stub End).

Stub End
A Stub End always will be used with a Lap Joint flange, as a backing flange.
This flange connections are applied, in low-pressure and non critical applications, and is a cheap method of flanging.
In a stainless steel pipe system, for example, a carbon steel flange can be applied, because they are not come in contact with the product in the pipe.

Threaded Flange

Threaded Flanges are used for special circumstances with their main advantage being that they can be attached to the pipe without welding. Sometimes a seal weld is also used in conjunction with the threaded connection.
Although still available in most sizes and pressure ratings, screwed fittings today are used almost exclusively in smaller pipe sizes.
A threaded flange or fitting is not suitable for a pipe system with thin wall thickness, because cutting thread on a pipe is not possible. Thus, thicker wall thickness must be chosen...what is thicker ?

Blind Flange

Blind Flanges are manufactured without a bore and used to blank off the ends of piping, valves and pressure vessel openings.
From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed flange types.

Flange Faces

Different types of flange faces are used as the contact surfaces to seat the sealing gasket material.
ASME B16.5 and B16.47 define various types of flange facings, including the raised face, the large male and female facings which have identical dimensions to provide a relatively large contact area.
Other flange facings covered by these standards include the large and small tongue-and-groove facings, and the ring joint facing specifically for ring joint type metal gaskets.

Different types of faces

  • Raised Face (RF)
    The raised face flange face is the most common type used in process plant applications, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face
    This face type allows the use of a wide combination of gasket designs, including flat ring sheet types and metallic composites such as spiral wound and double jacketed types.
    The purpose of an RF flange is to concentrate more pressure on a smaller gasket area and thereby increase the pressure containment capability of the joint
  • Flat Face (FF)
    The flat face flange has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.
    Flat face flanges are never to be bolted to a raised face flange.
  • Ring-Type Joint (RTJ)
    This type is typically used in the most severe duties, for example, in high-pressure gas pipe work.
    Ring-type metal gaskets must be used on this type of flange facing
    The ring-type joint flanges are typically used in high-pressure and/or high-temperature services above 800°F (427°C).
    They have grooves cut into their faces which steel ring gaskets. The flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or Coining) the gasket to make intimate contact inside the grooves, creating a metal-to-metal seal.
  • Tongue and Groove (T&G):
    These flanges feature matching grooves and raised sections. This aids in installation as the design helps the flanges to self-align and provides a reservoir for gasket adhesive.
  • Male & Female (M&F):
    Similar to tongue and groove flanges, these flanges use a matching pair of grooves and raised sections to secure the gasket. However, unlike tongue and groove flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.

Materials for Flanges

Pipe flanges are manufactured in all the different materials like stainless steel, cast iron, aluminium, brass, bronze, plastic etc. but the most used material is forged carbon steel and have machined surfaces.

In addition, flanges, like fittings and pipes, for specific purposes sometimes internally equipped with layers of materials of a completely different quality as the flanges themselves, which are "lined flanges".

The material of a flange, is basically set during the choice of the pipe, in most cases, a flange is of the same material as the pipe.

All flanges, discussed on this website fall under the ASME en ASTM standards, unless otherwise indicated. ASME B16.5 describes dimensions, dimensional tolerances etc. and ASTM the different material qualities.

Advantages and Disadvantages of Flanged Connections VS Welded Connections

There are no standards that define whether or not flange connections may be used.
In a newly built factory is customary to minimize flange connections, because only one weld is needed to connect two pieces of pipe. This saves the costs of two flanges, the gasket, the stud bolts, the second weld, the cost of NDT for the second weld, etc.

Disadvantages
– Each flange connection can leak (some people claim that a flange connection is never 100 percent leak proof).
– Flanged pipe systems need much more space (just think of a pipe rack).
– Insulation of flanged pipe systems is more expensive (special flange caps).

Advantages
– A new line can contain multiple pipe spools and can be manufactured in a workshop.
– This pipe spools can be assembled in the plant without the need to be welded.
– NDO (X-ray, Hydro test etc.) in the plant is not necessary, because this has been done in the workshop.
– Blasting and painting in the plant is not necessary, because even this has been done in a workshop (only paint damages during installation should be repaired).

As with many things, everything has its pros and cons.

What Information Do You Need When Selecting a Flange?

  • At what pressure will your application be operating?
  • At what temperature range will your application be operating?
  • What is your application? Water service? Air Piping? Chemical Piping? Process Piping? High-Pressure Oil or Gas? These questions will likely drive whether you have a pressure requirement.
  • hat material is required for your application? ANSI and AWWA flanges are most commonly supplied in common carbon steel like A105, however the ANSI B16.5 specification covers a wide variety of materials including high-yield carbon materials, stainless materials and alloys. The AWWA C207 and C228 specifications cover carbon and stainless materials.
  • Does your application require the welded slip-on, a weld neck flange or a loose backup type lap joint flange?
  • If you require a weld neck flange, what is the inside diameter/bore size of the pipe you will be welding to?
  • Are there any specialized gasket requirements? Each flange specification designates the allowable options for gaskets.
  • Are there any specialized bolt requirements? Each flange specification designates the allowable options for bolting
  • Other considerations: coating, oil, paint, epoxy, galvanizing
  • What is your flange mating up with? If your flange mates up to the same type of flange then there are no issues, but if your flange mates up to something else, then understanding the bolt pattern of the existing flange is critical. There are a wide variety of flange specifications, and it will be critical to know what the existing flange spec is so you can assure that the bolt pattern will mate.

Contact us at sales3@openex.com.cn or call us at +86 186 5928 0806 for more information about manufacturing for flanges and to receive a free project quote today.

About Openex

Openex is home to a full-service, one-stop-shop, contract manufacturing company producing custom large machined parts and fabrications. Our full large fabrication services including large machining, cutting, welding, rolling, punching, braking, testing, painting, and others.
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