Understanding Pipe Flanges: Application, Types, and Benefits

A pipe flange has several components: a 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 pounds. While they are available in several diameters, the larger flanges are available in the higher pressure class/rating.

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Flanges also have several types of facing which include: flat face, ring-type joint, lap joint, tongue & groove and raised face. The 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 applications. Always 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 system. As 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 pipe. They 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 systems. This type slips onto the pipe and the fillet weld is applied at both the top and bottom of the pipe flange. These welds provide extra strength and prevent leakage. While 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 fluids. The 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 pipes. Given their threaded connection, they do make it easy to disconnect the piping system.

Weldneck flanges have a long neck that is butt welded to pipe. This type is also known as a weld bend flange. Since the bore of the neck matches that of the pipe, it reduces erosion and turbulence.

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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
Blind	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
Slip-On/Hubbed	Cooling water lines Firefighting water lines Oil, gas & steam process lines
Socket Weld	Hydraulic pipes
Threaded	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
Aluminum	Ideal for lightweight requirements Great weight-to-strength ratio Corrosion resistant due to surface microscopic oxide layer
Brass	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
Copper	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
Titanium	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