Spiral Wound Gaskets

Give the flange standard and rating (JIS 10K, DIN PN10/PN16, ASME Class 150/300), the nominal size, and the type (R, IR, OR, IOR). Then give the winding metal, the filler, and the inner and outer ring materials. Flexitallic’s ordering example lists exactly these: style, nominal pipe size, pressure rating, gasket standard, winding materials, outer ring material and inner ring material. The IMPA lines end "W/MORE DETAILS" because these must be added.^[3]

Flexitallic’s standard build is a type 304 stainless winding, flexible graphite filler and a carbon steel guide ring. 316L and other winding metals, and PTFE, mica and ceramic fillers, are also made. Choose the filler for the service temperature and medium. Flexitallic warns that PTFE starts to decompose slowly above 250 °C.^[3]

For raised-face and flat-face flanges, order the ringed types. Flexitallic’s selection guide gives the outer-ring style for general duty. It gives the inner-and-outer style for high pressure or temperature, PTFE filler, corrosive service and cycling. A winding-only gasket needs a compression stop built into the flange (tongue, groove or recess depth), or it can be over-compressed and fail.^[3]

ASME B16.20 (since 2008) requires inner rings on all spiral wound gaskets with PTFE filler. It makes them the default for flexible graphite filler unless the purchaser says otherwise. For all fillers they are required at NPS 24 and larger in Class 900, NPS 12 and larger in Class 1500 and NPS 4 and larger in Class 2500. To get a graphite gasket without an inner ring, the order must say so.^[2]

The outer ring is colour coded under the ASME B16.20 scheme. A solid colour shows the winding metal, for example yellow for 304 and green for 316L. Stripes show the filler, such as grey for flexible graphite and white for PTFE.^[3][1]

At assembly, ringed gaskets are tightened down to the guide ring, which is there as a compression stop. Flexitallic gives flange faces a turned finish of Ra 3.2 to 6.3 µm and asks for lubricated bolts. Its low-emission spiral wound gasket sheet adds: no gasket pastes, and the gasket is not to be re-used.^[3][4]