Semi-Metallic gaskets are built with a combination of metal and non-metallic materials. The metal guarantees strength while the non-metallic component provides conformability and sealability to the gasket. The most common semi-metallic gaskets are the spiral wound gaskets (introduced by Flexitallic at the beginning of the past century) and Kammprofile gaskets (or Camprofile gaskets), and a variety of metal-reinforced graphite gaskets.

Spiral wound gaskets are available in different configurations depending on the number of rings and material grades combination of the inner rings and the outer rings of the gasket. Semi-metallic gaskets can withstand most operating conditions (pressure and temperature conditions), and are used on raised face flanges (RF), male-and-female flanges (M&F), and tongue-and-groove flanges (T&G). Semi metallic gaskets can be grouped in the following categories:


    Spiral wound gaskets

Flexitallic USA launched on the market spiral wound gaskets back in 1912 to cope with the demand for leak proof flanges seals in condition of increasing temperatures and pressures. Spiral wound gaskets are designed to withstand the mechanical stress generated by severe and fluctuating service conditions on the flanges, the gaskets and the bolting sets of the flanged pipeline joints. A spiral wound gasket has, as key sealing element, a formed metal strip. The sealing strips or fillers are usually made of graphite, even if different materials such as PTFE may be used, and the windings are generally made of stainless steel. The gasket is fitted into a steel ring of a specific thickness. When the gasket is fitted with a flange and a bolt load is applied, the steel outer ring of the gasket creates the sealing. To further improve the pressure rating of the spiral wound gasket, a steel ring may be added in the internal part of the gasket (the so-called inner ring). This gives an additional compression and provides a heat and corrosion barrier protecting the gasket windings and the flange from erosion. The inner ring material may be, or not, of the same of the winding metal. The usage of a solid metal inner ring is required by ASME B16.20 for pressure class 900, NPS 24 and larger, pressure class 1500 NPS 12 and larger, pressure class 2500, NPS 4 and larger.



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