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Raised Face Flange vs. Flat Faced Flange

The key identifier between the raised face and flat face flange is that the raised face is raised above the bolting circle face.  The raised face and flat face flanges are both industry standard in the pipe fitting and flange industry.  This post will showcase details on the differences and uses of the raised face and flat face flanges.

Raised Face Flanges

Raised Face Finish on Flange manufactured at Coastal Flange

The raised face (RF) is the most common type of flange facing used. It is called a raised face flange because it has a raised surface above the bolting circle where the gasket is placed.  These flanges are widely used in oil and gas pipelines. They are appropriate for both high and low temperatures and pressures.

The main purpose of the RF flange is to concentrate the contact pressure on the gasket area, resulting in increased strength of the seal. Diameter and height are in ASME 16.5 defined by pressure class and diameter. The higher the pressure rating, the larger the diameter of the flange, the number of bolts and thickness of the flange itself, and the raise face are.  The Standard Flange Facing for ASME B16.5 and ASME B16.47 is a 125-250 RMS Finish.

 Flat Face Flanges

Large Diameter Custom Ring with Flat Face Finish

Flat face (FF) flanges are similar to raised face flanges, but they have a flat surface.  These flanges have a gasket surface in the same plane as the bolting circle face.   The flat face is the simplest type of flange face available.

The intention of a flat face flange is to prevent the bending movement that is put on flanges as the bolts are torqued. Usage of flat face flanges are those in which the mating flange or flanged fitting is casted. FF flanges can be seen in low-pressure and low temperature situations like in water treatment facilities. The finish for the ASME B16.47 flat face flanges is the same as the raised face with a finish of 125-250 RMS.

How to Choose the Right Flange for your Project

When it comes to the best flange face for your project there are many factors such as pressure, temperature and purpose. Flat face flanges are best for operations with low pressure and low temperature.  Raise face flanges are designed to endure more challenging situations. To learn more about how to order a custom flange with us, click here!

Our expert sales team and engineers at Coastal Flange are available to assist you with your next project.  We can help you find the right flange and face for your needs.

Contact Coastal Flange with any questions or to receive a quote tailored.
Phone:  713-937-3333

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