Re: Flange Facing

My reply is based upon raised faced flanges, which are the more commonly used flanges in the chemical processing industry. The smaller the Ra number the smoother the finish. The terms "CLA", "AA" and "Ra" mean exactly the same thing. The finish requirement can cost more when you specify out of the mid-ranges (250-500 Ra). The roughness average thats required for a specific gasket, to seal properly, can be found under the gasket manufactures data sheets/catalogs. FYI: Flexitallic sells (or at least use to) a machined face comparison scale. Its neat. The name is "Microsurf Electro-formed Surface Roughness Comparison Scales. The scale shows comparisons from 16Ra thru 2000Ra. You can use your fingernail to get an excellent feel for the different serrations. This sample makes a good "show and tell" for training classes ect.

• Original Message ----- From: Paul Bowers <pbowers@pipingdesign.com> To: <PipingDesign@yahoogroups.com> Sent: Wednesday, June 06, 2001 8:47 PM Subject: [PipingDesign] Flange Facing

> TYPES OF FLANGE FACINGS
>
> Gaskets of different materials are used to provide a seal between
> the mating flanges. In order for the gaskets to be effective, the
> facing of the flange has to be machined to specific dimensions and
> tolerances in accordance with the type of gasket to be used. The
> gasket faces referenced in this web site and normally supplied
> are:
>
> a. Raised Face
> b. Flat Face
> c. Ring Type Joint (RTJ)
>
> In addition, special application facings are available on request.
> These include the following:
>
> a. Small Tongue and Groove
> b. Large Tongue and Groove
> c. Small Male and Female
> d. Large Male and Female
>
> FLANGE FACING FINISH
>
> The flange facing most commonly used is the "raised face." It is
> referred to as a raised face because the gasket surfaces are
> raised .060" or .250" above the bolting circle face. Pressure
> rating of the flange determines the height of the raised face. The
> "flat face" or "full face" flange has a gasket surface in the same
> plane as the bolting circle face. Applications using flat face
> flanges or full face flanges are frequently those in which the
> mating flange or flanged fitting is made from a casting.
>
> Raised and flat flange facings are machined and may be either
> phonographic serrated or concentric serrated. The industry
> standard is a phonographic serrated finish. The facing finish is
> judged by visual comparison with Roughness Average (Ra) standards.
> Ra is stated in microinches (µin) or micrometers (µm) and is shown
> as an Arithmetic Average Roughness Height (AARH) or Root Mean
> Square (RMS). AARH and RMS are different methods of calculation
> giving essentially the same result and are used interchangeably
> for these products.
>
> The standard Ra supplied by the industry is 125 to 250 µin or 3.2
> to 6.3 µm AARH or RMS. Short form is 125-250 AARH or 3.2-6.4 AARH.
> Smoother or rougher finishes are available at the customer's
> request.
>
> The gasket contact surface for a ring joint (RTJ) flange is inside
> the groove cut into the face. The steel ring gasket fits into the
> grooves of the mating flanges and is sealed with pressure. The
> finish in the ring grooves and on the ring gasket is 63 µin AARH
> or 1.6 µm AARH maximum.
>
> Facings for tongue and groove or male and female faces are
> provided in accordance with customer requirements.
>
> <a href="http://www.boltex.com/facings.htm">http://www.boltex.com/facings.htm</a>
>
>
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Received on Thu Jun 07 10:49:00 2001