Ah,
Would have been good to have that included in the OP....
It certainly isn't an R9 O ring then.
Or a class 900 flange.
Or an RTJ type flange.
"ANSI" hasn't been used for decades to describe flanges so this may be something which was included in a much earlier edition of the code and just left there. The history section of ASME B 16.5 refers to flange finished in their 1996 version when it changed to ASME B 16.5.
The current version in 6.4.5.3 just lists dimensions / roughness in microns and no mention of an R number.
So I'm out of ideas unless you can find a version of the flange code from 1996 or earlier which mentions this.
This is the closest I can find from the 1996 edition where Ra might be the R you are looking at?
Face Finish. The finish on the face of a flange is
measured as an Arithmetical Average Roughness
Height (AARH). The finish is determined by the
standard used. For example, ANSI B16.5
specifies face finishes within a range 125AARH -
500AARH (3.2 Ra to 12.5 Ra). Other finishes are
available on request, for example 1.6 Ra max,
1.6/3.2 Ra, 3.2/6.3 Ra or 6.3/12.5 Ra. The range
3.2/6.3 Ra is most common.
Maximum now is 6.3 micron (250 micro inches).
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