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Flatness Tolerance

Some of our customers often wonder about flatness being an issue with regards to aligning flanges properly on their equipment, or for the purposes of general aesthetics/symmetry for non-industrial applications.

To the best of our knowledge, there is no flatness tolerance in any published flange specification. Since flanges are made on lathes from oversized forgings, the probability of having an issue is near zero.

That said, one can take a micrometer and check the thickness in multiple places against published thickness tolerances to “flunk” a flange whose flatness is seriously in question.

Texas Flange has never had an issue with flatness for any flanges we have supplied to our customers.

FLATNESS TOLERANCE

In some instances, it is important to take flatness into consideration when machining to certain dimensions.

This is almost exclusively a concern when a customer requires a large OD flange made to a very minimal thickness. As an example, if a customer requires a custom ring flange of a 60” diameter made to a half-inch thickness, we would not offer machining across the face due to the likelihood of “waffling,” but would offer mill finished from the plate.

This is essentially an attempt to reduce an issue with flatness for the finished/shipped product flange, and also to ensure the face finish is out of code. In these extreme cases,

Texas Flange may propose that your facing is done with Blanchard grinding or some alternative to the typical symmetry of a 125-250 RMS, so that although

The industrial standard for face finish is not practically achievable in this particular application, an asymmetric machine finish is provided in order to accommodate the friction needed in the gasket sealing process of your installation.

Texas Flange is always trying to be of the best service to our customers.

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Mohd Azrul Azman
3 years ago

HI, could you explain how check flange circumferential and radial tolerance?…ASME PCC-1 provides the tolerance.thanks

texasflange_pt_admin
3 years ago

This is more an issue with hardware than with flanges. I’ve not come across it since these are not dimensions for which ASME B16.5 or its cousins give tolerances. One could “flunk” a flange with say, uneven drilling, via measuring the diameter multiple times or checking the spacing between each hole. See page 13 of our catalog for published tolerances. Thank You!