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When comparing a raised face flange and a flat face flange, wha

  • The raised face flange has a raised region around the pipe bore, whereas the flat face flange does not have such a raised region around it. Both of these flange faces are commonly encountered. A ring gasket or a full-face gasket can be used to seal them. This page will cover raised face flanges, flat face flanges, and the gaskets that go with each of these types of flanges.


    Y strainer with Raised Face Flange made of carbon steel

    Raised face flanges are the most common type of flange  The term "raised face" refers to the fact that it has a raised surface above the gasket bolting circle. Using a soft, flat, or semi-metallic gasket between the flanges, the elevated portion of the flanges can be sealed.

    Raised face (RF) flanges are commonly found in process plants, but they can be found almost anywhere. They perform admirably under high temperatures and pressures. Due to the smaller gasket area, the RF flange increases the pressure-containment capabilities of the joint.

    Pressure ratings are used to determine the size of flanges. Its diameter, bolt count, and thickness all increase as the pressure rating of the device increases.

    Raised face flanges can be used on duplex and Y-strainers, to name a few applications.

    Duplex basket strainer with a flat face flange

    Although they are similar to RF flanges, they do not have the elevated region that is found on RF flanges. Instead, everything is level. In other words, the gasket for the FF flange seals the entire surface where the two flanges come together. Gaskets for FF flanges are typically made of nonmetallic materials such as Viton (a fluoroelastomer) or EPDM (ethylene-propylene diene monomer).

    When the bolts are torqued, the FF flange is used to prevent the bolts from bending. Some flange materials, such as cast iron and fiberglass, are brittle and can break easily. FF flanges are the solution to this problem.

    These flanges are used in applications that are less demanding, such as low-pressure water pipelines. Pump suctions or water treatment flanges are examples of low temperature and pressure applications.


    The Gaskets for Flanges
    There are two types of gaskets available for sealing raised or flat face flanges: full-face and ring-type. It is critical to understand which type is appropriate for your application as well as the measurements necessary to purchase them.

    Ring Gasket is a gasket that surrounds the ring of a ring.
    The rig gasket is compatible with both RF and FF flanges. In addition to being positioned on the elevated surface of the RF flange, it also surrounds and fits inside the pipe bore and the flange bolts. It is necessary to disassemble the joint in order to install the ring type gasket. It requires more material and cutting than a full-face gasket, but it is more difficult to clamp into place.

    Ring gaskets must have the ID (inner diameter or pipe bore size), OD (outer diameter), and gasket thickness measured before they can be used.


    Gasket on the Front
    In addition to RF flanges, the full-face gasket is used with flat face flanges to seal against leakage. It is elevated on the flange faces, but it has the same outside diameter as the other components. As a result, it requires holes to allow the flange bolts to slide through. This allows for easier gasket alignment, but it necessitates the dismantling of the joint. Because it extends to the outside diameter, the full-face gasket prevents dirt from entering the joint.

    Full-face type gaskets require the following dimensions: ID, OD, bolt circle diameter, number of bolt holes, and gasket thickness.

    RF or FF Flanges: Which Should You Choose?
    It is critical to select the proper flange face, especially when high pressure or temperature are involved. In some cases, an RF flange is preferable because it is designed to withstand more severe conditions. The FF flange is preferable for lower pressure and temperature activities, as well as for systems made of cast iron, fiberglass, or other materials that may break when bolts are torqued.