Flange Serration

As per ASME B16.5:

• Tongue and Groove and Small Male and Female. The gasket contact surface finish shall not exceed 3.2μm (125 μin.) roughness.
• Ring Joint. The side wall surface finish of the gasket groove shall not exceed 1.6 μm (63 μin.) roughness.
• Other Flange Facings. Either a serrated concentric or serrated spiral finish having a resultant surface finish from 3.2 to 6.3 μm (125 to 250 μin.) average roughness shall be furnished. The cutting tool employed should have an approximate 1.5 mm (0.06 in.) or larger radius, and there should be from 1.8 grooves/mm through 2.2 grooves/mm (45 grooves/in. through 55 grooves/in.).
  

I am a bit confused. The surface finish of the serrated area shall be 3.2 to 6.3 microns? If it is serrated at 1.8 grooves/mm, which surface roughness is it referring to? On the slopes of the grooves? At 1.8grooves/mm the pitch of the groove shall be 0.056mm, how could a tool with a 1.5mm radius produced the grooves?

I have read this exact note on a fabrication drawing and I cannot really understand it. Please help.

Sir

I want to know about depth of serration.Pl. try to explain me because in some flage i show less depth serration where as in some flange i found more depth serration.

For ASME raised face flanges, I will repeat ............

Either a serrated concentric or serrated spiral finish having a resultant surface finish from 3.2 to 6.3 μm (125 to 250 μin.)

Of course, these are based on Arithmetic Average Roughness Height (AARH) or Root Mean Square (RMS) which are different methods of calculation giving essentially the same result and are used interchangeably for these flange surfaces. So it is allowed (expected) that there will be variations from flange to flange - but within the tolerance above.

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