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Pipe Flanges

What is a Pipe Flange?

Pipe flanges connect piping and the components of a piping system such as valves, fittings, pipe with each other and specialty items using bolted connections and gasketsThey can be installed in several fashions including:  welding, lapping or screwing.

There are several benefits to using a pipe flange including:  it provides a secure connection between pipes, valves & other equipment; it allows for quick disassembly by providing installation or modification access points; and it increases the strength at the joint.

The application and type of flange determine the way in which the connection is made.  Always consider the fluid being conveyed through a pipeline, the operating temperature, flange type, size, pressure class/rating and other specifications prior to installation.  This ensures safety during installation and operation of the piping system.


A pipe flange has several componentsa unique bolt pattern, connection type (e.g. socket weld, threaded, slip on, etc.) and face.  They have varying bolt patterns that are based on the type of flange and its diameter.  It is important to note that flanges do require a gasket to make the seal except for ring-type joint faces.

Pipe Flange Assembly


Pipe flanges can be manufactured from a casting (cast from a mold) or forging (using energy to change the shape of billet/ingot)They also come in various pressure ratings:  150, 300, 600, 900, 1500 and 2500 poundsWhile they are available in several diameters, the larger flanges are available in the higher pressure class/rating.


Flanges also have several types of facing which include:  flat face, ring-type joint, lap joint, tongue & groove and raised faceThe facing is the area that is used to seal the flange.

Ring Face Types

 Learn More About Face Types

Industry Flat-Full Face Raised Face Ring-Type Joint Face
Cast-Iron Equipment X    
High Pressure/High Temperature (up to 1382°F/750°C)     X
Low-Pressure Water Pipe Systems X    
Process Plants (Chemical, etc.)   X  
Oil & Gas   X X
Valves X    

Serrated Face

The face itself can be serrated or smooth There are several industries that traditionally require a specific type of facing.


There are several types of pipe flanges in a piping system; but there are 6 main types – blind, lap joint, slip on, socket weld, threaded and weld neck Each of them has properties that determine their use in commercial, industrial and institutional applicationsAlways consult your project manager prior to installing any pipe flange into any application.

  • Blind flanges have no center hole and are used to seal off a piping systemAs a result, one can easily execute pressure tests cost effectively
  • Lap Joint flanges use a stub end (Type A, B or C) and slide over the pipeThey are also known as loose-ring flanges and back-up flanges.  Lap joint is used with lapped pipe and allow for frequent cleaning and inspection through dismantling.  They are very durable and can be used because the fluid conveyed in the system does not come in contact with the flange.
  • Slip On flanges, also known as hubbed flanges, are thinner than other flanges and are traditionally used in low pressure systemsThis type slips onto the pipe and the fillet weld is applied at both the top and bottom of the pipe flangeThese welds provide extra strength and prevent leakageWhile the installation is low cost and easy, the welding does add cost to its installation.
  • Socket Weld flanges are designed for small size, high-pressure piping systems that do not carry corrosive fluidsThe pipe is inserted into the socket and a single fillet weld on the outside of the flange is applied.
  • Threaded flanges are used in applications that are low pressure on smaller, thick walled pipesGiven their threaded connection, they do make it easy to disconnect the piping system.
  • Weldneck flanges have a long neck that is butt welded to pipeThis type is also known as a weld bend flangeSince the bore of the neck matches that of the pipe, it reduces erosion and turbulence.


There are other types of flanges including:  orifice, reducing, ductile iron backup, copper solder joint and many more.


What are the Applications of Pipe Flanges? 

Type Traditionally Used In
  • Creating piping system access points
  • Permanent seal to a piping system
  • Pipe pressure testing
  • Temporary seal for system repairs
Lap Joint/Loose Ring
  • Frequent dismantling for maintenance
  • Low-pressure applications
  • Cooling water lines
  • Firefighting water lines
  • Oil, gas & steam process lines
Socket Weld
  • Hydraulic pipes
  • Applications that are flammable, hazardous, or explosive & cannot be welded due to safety concerns
  • Restricted space where welding is not feasible
  • Small pipe sizes
Weld Neck/Weld Bend
  • Conveyance of volatile and hazardous fluids
  • Piping systems with bends that are repeating
  • System conditions that have wide fluctuations in pressure & temperature


Flanges are available in several alloys including:  copper, brass, stainless steel, carbon steel, titanium, aluminum, superalloys, tool steel and alloy steel.  Each alloy carries specific attributes:

Alloy Attributes
Alloy Steel
  • Iron-based with <4% Chromium
  • Resistant to wear & tear
  • Strong
  • Ideal for lightweight requirements
  • Great weight-to-strength ratio
  • Corrosion resistant due to surface microscopic oxide layer
  • Highly conductive
  • Copper, Tin and Zinc alloy
  • Nonmagnetic
  • Corrosion resistant
  • Resists higher heat & electric conductivity compared to other metals
Carbon Steel
  • Low & high carbon steels available
  • Ductility, impact strength, wear resistance and hardness determine its need
  • Nonmagnetic
  • Compared to other materials, can sustain greater loads
  • Corrosion resistant
  • Can handle high-temperatures
Stainless Steel
  • Corrosion resistant
  • Durable
  • Withstands pressure & high temperatures
Super Alloys
  • Tolerates severe conditions
  • Material makeup includes Nickel & Cobalt
  • Resists acid corrosion & high temperatures
  • Lightweight
  • Strength is exceptional
  • High heat resistance
  • Very costly
Tool Steel
  • Made from tool steel billets/ingots
  • Impact resistance & robustness is strengthened because it includes carbon & other alloys that react with iron
  • Durable


Merit offers several types of flanges in various alloys:   


Merit Brass Pipe Flanges




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