Flange, abbreviated as FLG, is a bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system.  Flanges provide access for when equipment (or piping) needs to be cleaned, inspected or reconfigured.   A flange pair is made up of two flanges and a gasket with bolts and nuts.  Pipe flanges come in different styles, pressure ratings, materials and sizes to meet the design requirements.  In the oil field, the two most commonly used flange standards are ANSI/ASME B16.5 and BS 1560.  API Spec 6A is for flanges used on wellhead and christmas tree equipment.

Flanges of different standards or materials are not normally joined together.  There are instances where the design may require dissimilar metals or different classifications are required to be bolted together.  When this happens, be sure to seek engineering advise to ensure that the design is still within compliance with the applicable standards and specifications.

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Pipe Flange Design Classification

There are six basic types of flanges and are described by the way the connect to the piping system.  Click on the links below to be taken to a page detailing the different types of flanges.

Specialty Pipe Flange Design Classification

Pipe Flange Classes

Only the most used flange classes are listed on this page.  For more information on flanges and their respective standards, please follow the link below.

Pipe Flange Pressure Classes

Flanges are normally manufactured in seven basic ratings: 150 Lb, 300 Lb, 400 Lb, 600 Lb, 900 Lb, 1500 Lb and 2500 Lb.  The ratings can be expressed in different ways but mean the same thing - 150 Lb, 150 Lbs, 150# or Class 150.

Each class of flange can handle more pressure than the previous class because of its construction.  The higher the class is, the thicker the metal is.  Thus a higher pressure can be handled.  There a numerous factors that can affect the pressure capability of a flange, such as the type of metal that is used.

Pipe Flange Facing

There are three primary types of flange facings.  Not all facings are available with each end connection.  This is based on the design of the flange and design of the piping system.  The typical flange facings are:

• Raised Face Flanges (RF)
• Flat Face Flanges (FF)
• Ring Type Joint Flanges (RTJ)