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Spiral wound gaskets: performing under pressure - Part 2


(continued from part 1)
 
The total thickness of a spiral wound gasket varies between 2.5 and 7.3 mm, but most common thickness of a spiral wound gasket is 4.5 mm.
 
Spiral wound gaskets are widely used in refineries, chemical, gas and high-pressure applications such as in power plants. They are available from DN10 up to diameters of 4 meters and more, but for sizes above 2 meters a kammprofile-gasket is recommended.
Spiral gaskets can be fitted with (metal enveloped) partitions, welded to the inside of the metal spiral, for example for separating the different compartments in reaction vessels or heat exchangers.
 
 
Figure 2 : Basic production method of spiral wound gaskets.
 
The spiral wound gasket can be provided with an inner or an outer ring, or both. This solid metal ring serves to reinforce the gasket, it limits the compression and avoids the destruction of the gasket. The ring is thinner than the actual sealing element.
The inner ring is in contact with the medium and therefore usually in the same material as the metal strip of the coil seal. The inner ring also prevents any flow of filler material such as PTFE, fill the crack area to prevent accumulation of particles between the flanges and thereby reduces turbulence and erosion. It also prevents “inward-buckling" of the windings, especially for large spiral wound gaskets.
The outer ring also prevents blow-out and facilitates centering between the flange bolts. The outer ring is usually in the low carbon steel, but can also be made in stainless steel.
 
To obtain a good seal the flanges used with a spiral wound gasket should have the appropriate finish or surface roughness. Typically, a surface roughness (Ra) between 3.2 and 6.3 μm (RMS 125-250) is recommended for spiral gaskets with graphite.
 
Because of their metal components spiral wound gaskets are very strong, easy to handle and are cheap because of high production volumes (for standard flanges). The relatively non-sticky character makes them easy to remove and cause basically no damage to the flange. They can withstand high surface pressures and provide good sealing, even at high temperature and pressure fluctuations. They are typically used at pressures greater than 40 bar and temperatures ranging from cryogenic (-198 °C) up to 1000 ° C.
 
Spiral wound gaskets usually are round. Other forms exist, but are unusual.
Some manufacturers use a color code to indicate which of the spiral gasket material is manufactured. This may help to identify spiral wound gasket that is still in between pipeline flanges, although in practice (dirt, low-light conditions ,...) it is not always clearly distinguishable.
 
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