Spiral Wound Gasket Rest Face Surface Roughness

Being a more compressible material, won't it simply be a mould of the surface it is compressed against, once the bolts are flogged-up?

The spiral wound gasket consists from inner and outer steel flat rings, and in between there is third ring for sealing which composed from spiral tape of stainless steel filled with asbestos. And the thickness of sealing ring is higher than the thickness of other supporting rings, so the inner and outer rings may be furnished with flat surface. And when tightening the stud bolts connecting the mating surfaces of flanges, the asbestos -in between spirals- is compressed and enable good sealing.

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Note. After using and dismantling of gasket, you can easily see the marking of flange serration on surface of gasket sealing ring.

GA...

PS - Filler material these days is graphite (and other non-asbestos materials).

Many raised sealing faces have machine markings in the form of rings, while many are finished to a flat smooth surface . Perhaps the finish varies per manufacturer, which therefore implies no standard ?

The coarser finish may be an advantage in an environment where the flanges are prone to rough handling, since the sealing-face base surface is protected from minor mechanical damage (indentation/ scoring) to a degree, and the gasket will still seal due to it's compressibility.

Suggest you consult a gasket or flange manufacturer if you have specific concerns.

What do you mean by" finish of rest face of spiral wound gasket". Spirals as you might have noticed are made of 0.4mm SS tape generally in "V" shape and in between two layer filler gasket material like PTFE or Graphite or Asbestoss or any other fibrous material is filled in form of continuous tape and its assembled surface finish is genrally rough but in a plane.

Inner guide ring and outer guid rings are not suppose to come in contact with the raised faces of the matting flanges, however their finish is generally not of much concern but genrally machined finish.

I think you are on the right path to answering the OP's question. The finish of the Inner and outer solid metal rings of the gasket does not matter.

However, your comment "that the Inner guide ring and outer guide rings are not suppose to come in contact with the raised faces of the matting flanges" is incorrect. These Rings or at least the Outer Ring does come in contact with the flange raised faces as a stop to prevent overcompression of the "spiral rings".

Agreed.

I thought the question was posed incorrectly, because it didn't make much sense to me, so I answered to what I interpreted to be the actual query.

Go figure...

Normally outer and inner guide rings are of same thickness. Gakset is crushed to hold the leakage through flange joint. If you are crushing your spiral wound gasket to make raised face contact the outer guide ring in that any future disturbance will need replacement of gasket. You will not be able to re-tighten the flange joint to hold minor leakage if any in case of process upset etc. Yes it may be used as indication that if you have tightened your flanges to the limit that raised faces have touched outer guide ring, then in next opportunity you should replace this gasket.