The size of a spiral wound gasket is not a free choice; the standard and class of the flange it belongs to already define it. State size and class correctly and the rest follows from the standard.
Four dimensions define a gasket
| Dimension | What it sets |
|---|---|
| Winding inside diameter | The edge facing the fluid; matches the inner ring where fitted |
| Winding outside diameter | The outer limit of the sealing band |
| Inner ring bore | Close to the pipe bore, without protruding into the flow |
| Outer ring outside diameter | Seats against the inner limit of the bolt holes |
The outer ring centres the gasket between the bolts, so its diameter follows the bolt circle. Winding thickness is a separate parameter, selected by diameter.
Which standard for which flange
- ASME B16.20: ½"–24" for ASME B16.5 flanges, Class 150–2500; 26"–60" for B16.47 Series A and B.
- EN 1514-2 / EN 12560-2: For EN 1092-1 and EN 1759-1 flanges, in PN and DN.
- GOST R 52376: For GOST 12815 flanges.
- BS 3381: For BS 1560 flanges.
The gasket follows whichever standard the flange belongs to. At the same nominal size, ASME and EN gasket dimensions differ; mixed, the gasket either touches the bolts or protrudes into the flow.
CG, CGI and other codes
Type codes are used as shorthand:
- R: Sealing element only, no rings
- CG: With outer (centring) ring
- CGI: With inner and outer rings
- RIR: With inner ring only
Writing the code on the enquiry prevents the configuration being misread. See technical data and type selection for the choice itself.
Non standard sizes
Heat exchanger covers, handhole covers and non standard equipment connections need shapes other than round: oval, elliptical and bar types. These do not come from a table; they are produced from a sectional and dimensional drawing.
What to state on the order
One line should carry: standard (such as ASME B16.20), nominal size, pressure class, type code (CG/CGI), winding material, filler material, inner and outer ring material, thickness if non standard, and quantity.
Example: *ASME B16.20, 6", Class 300, CGI, 316L winding / graphite filler, 316L inner ring, carbon steel outer ring — 12 pcs.*
Send your list at that level of detail: enquiry form. See our gasket page for the product group.
FAQ
Is gasket size the same as flange size?
No. Gasket dimensions are defined in the standard by flange standard and pressure class; given size and class, the dimensions follow.
What is the difference between CG and CGI?
CG has an outer ring only, CGI has both inner and outer rings.
Can non standard sizes be made?
Yes. Oval, elliptical and special section gaskets are produced from drawings.
Send us your material list; we reply with price and lead time the same day.
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