Flanges are an integral part of a pipeline network. They provide the connections necessary to link pipelines with the nozzles on mechanical equipment or with adjoining pieces of pipline. While flanges themselves have different pound ratings to indicate the pressure and temperature ranges that they can work to, the actual flange faces themselves vary according to environment within which they will be used. Faces are the mating surface of a flange, nozzle or valve. Flange faces have to be smooth enough to ensure they provide a tight, leak-free seal with the flanges are bolted together. For the purpose of this article we will be focusing on three common types of flange faces; flat faces, raised faces and ring type joints.
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It will come as no surprise that flat faces has a flat surface. Forged steel flat face flanges are often found 150# and 300# ratings. Flat face flanges are used "are used on pump facings or on fiberglass flanges where the torque of compressing the gasket will damage the flange body" and on cast iron flanges sometimes found on mechanical equipment that can cause complications due to the brittle nature of cast iron.
Raised Face Flanges
The most commonly used flange face, raised face flanges have a raised surface inside of the bolt circle. The height of the raised surface varies according to the pound rating of the flange. Flanges with 150# or 300# have a 1/16" raised face whereas 400# or more have 1/4".
It is important to take note of whether the raised face is included within dimensions charts when dealing with pipeline components as Pipe Drafting and Design warns:
"The 1/4" raised face thickness is not always included in the length dimensions for 400# and higher pound ratings. To assure accurate dimensioning, always determine if the dimensioning chart being used includes the 1/4" raised face thickness for the larger pound rating flanges. The 1/4" raised face thickness must be added to the dimensioning chart measurement to obtain the overall flange length if the dimensioning chart indicates it has not been added."
Ring-Type Joint Faces
Ring-type joints (RTJs) are considered to be the the most efficient flanges for use in pipeline design. Rather than using a gasket between connecting flanges, RTJs have a deep groove in a ring shared around the face. In this groove sits a metal ring which is compressed when the connecting bolts on the flange are tightened. This compression causes a tight, leak-proof seal on the connection.
Mirage Machines can provide the right tools to provide high quality surface finish restoration for each of these types of flange face. To find out more about our range of flange facing machines, download our flange facing machine buyers guide.
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