Flange Jointing System

Flange Information

Pipe flanges are protruding rims, edges, ribs, or collars used to make a connection between two pipes or between a pipe and any type of fitting or equipment component. Pipe flanges are used for dismantling piping systems, temporary or mobile installations, transitions between dissimilar materials, and connections in environments not conducive to solvent cementing.

Flanges are relatively simple mechanical connectors that have been used successfully for high-pressure piping applications. They are well understood, reliable, cost-effective, and readily available from a wide range of suppliers. In addition, the moment-carrying capacity of flanges is significant compared to other mechanical connectors. This is an important feature for systems that experience pipe-walking or lateral buckling from temperature and pressure variations (e.g. deep water lines). Flanges can be designed to meet a wide range of application requirements such as high-temperature and corrosion resistance. 


Pipe flanges have flush or flat surfaces that are perpendicular to the pipe to which they attach. Two of these surfaces are mechanically joined via bolts, collars, adhesives or welds.

Welding joins materials by melting the workpieces and adding a filler material. For strong, high pressure connections of similar materials, welding tends to be the most effective method of flange connection. Most pipe flanges are designed to be welded to pipes.

Brazing is used to join materials by melting a filler metal which solidifies to act as the connector. This method does not melt the workpieces or induce thermal distortion, allowing for tighter tolerances and clean joints. It also can be used to connect very dissimilar materials such as metals and metalized ceramics.

Threading is applied to flanges and pipes to allow the connections to be screwed together in a manner similar to nuts or bolts.

While the method of attachment can be a distinguishing feature, there are other considerations more important to pipe flange selection. Factors an industrial buyer should consider first are the flange’s physical specifications, type, material, and performance features most suitable for the application. 

Physical Specifications

First and foremost, a flange must fit the pipe or equipment for which it is designed. Physical specifications for pipe flanges include dimensions and design shapes. 

Flange Dimensions

Physical dimensions should be specified in order to size flanges correctly.

  • Outside diameter (OD) is the distance between two opposing edges of a flange’s face. This can a
  • Thickness refers to the thickness of the attaching outer rim, and does not include the part of the flange that holds the pipe.
  • Bolt circle diameter is the length from the center of a bolt hole to the center of the opposing hole.
  • Pipe size is a pipe flange’s corresponding pipe size, generally made according to accepted standards. It is usually specified by two non-dimensional numbers, nominal pipe size (NPS) and schedule (SCH).
  • Nominal bore size is the inner diameter of the flange connector. When manufacturing and ordering any type of pipe connector, it is important to match the bore size of the piece with the bore size of the mating pipe.

Flange Faces

Flange faces can be manufactured to a large number of custom shapes based design requirements. Some examples include:

  • Flat
  • Raised face (RF)
  • Ring type joint (RTJ)
  • O-ring groove

Types of Pipe Flanges

Pipe flanges can be divided into eight types based on design. These types are blind, lap joint, orifice, reducing, slip-on, socket-weld, threaded, and weld neck.

Blind flanges are round plates with no center hold used to close the ends of pipes, valves, or equipment. They assist in allowing easy access to a line once it has been sealed. They can also be used for flow pressure testing. Blind flanges are made to fit standard pipes in all sizes at higher pressure ratings than other flange types.