JIS standard Spiral Wound Gasket is a very effective sealing element made by spirally winding a 'V' shaped metal strip with soft filler material, usually flexible graphite or PTFE. This combination of resiliency and flexibility under varying conditions is very useful in the Oil, Gas and Petrochemical industries where fluctuations in temperatures across the flange face as well as bolt stress relaxation requires the gasket to recover and seal effectively under different operating conditions.
The outer centering ring is used to locate the spiral wound gasket concentrically within the flange and act as a compression limiter to prevent over-compression. It also provides additional radial strength, and reduces flange erosion, while protecting the spiral wound element and providing a heat shield and corrosion barrier to the flange.
This ring can be marked with the nominal size, pressure class and standard for ease of identification. The outer ring may be made of the same metal as the flange, but is commonly marked with the filler material (either a coloured strip or a pattern) for visual confirmation.
Using the right spiral wound gasket in a specific application is critical to its successful operation. It is important to consider the material and the design of the outer ring, the inner ring, the spiral elements, the flange and its bolts. This will ensure the optimal resiliency of the gasket.