The concept of spiral wound gasket construction was originated by Flexitallic in 1912, inaugurating the beginning of a new era in safe, effective sealing. The primary purpose for this development was the increasingly severe temperatures and pressures used by U.S. refinery operators in the first half of the century.

The necessity for a gasket to have the ability to recover cannot be over emphasized. The effects of pressure and temperature fluctuations, the temperature differential across the flange face, together with bolt stress relaxation and creep, demand a gasket with adequate flexibility and recovery to maintain a seal even under these varying service conditions. The Spiral Wound Gasket is the precision engineered solution to such problems, meeting the most exacting conditions of both temperature and pressure in flanged joints and similar assemblies and against virtually every known corrosive and toxic media.The spiral wound gasket meets the most exacting conditions of both temperature and pressure in flanged joints and similar assemblies and against every known corrosive and toxic media.

ASME B16.20 which covers spiral wound gaskets requires the use of solid metal inner rings in: Pressure Class 900, nominal pipe sizes 24 and larger, Pressure Class 1500 from nominal pipe sizes 12 and larger, Pressure Class 2500 from nominal pipe sizes 4 and larger and all PTFE filled gaskets. In the same standard is also described how a spiral wound gasket should be characterized, below you will find a image on it.

Basic Type

Basic construction type, inner and outer diameters are reinforced with several piles of metal without filler to give greater stability and better compression characteristics. - Suitable for tongue and groove, male and female or grooved to flat face flange assemblies.
 

Inner Ring Type

Solid inner metal ring acts as a compression stopper. To prevent accumulation of solids, reduce turbulent flow of process fluids and minimize erosion, damages of gasket between flange bore and the inside diameter, the annular space is filled up by solid inner metal ring. - Suitable for male and female pipe flanges.

Outer Ring Type

Solid outer ring accurately locates the gasket on the flange face to give the additional radial strength to prevent the gasket blowout and acts as a compression limiter. In case of installing the outer ring, it is very easy to install the gasket to flange face because the end of outer ring will touch at bolts - Suitable for use with flat face and raised face flanges. For class 900 and above an internal ring is recommended.

Inner & Outer Rings Type

A inner ring and outer ring type gasket will give an additional compression limiting stopper for gasket inner and outer side. It will prevent the corrosions on flange face at annular space. - Suitable for use with flat face and raised face flanges and specified for high pressure / temperature service - Class 900 and above or where corrosive or toxic media are present.