Bolted joint and gasket designers currently calculate spiral wound gasket stress in one of three ways. The differences lie in gasket area determination. The first is the historical Boiler & Pressure Vessel Code calculation method of using an effective sealing width which is half or less of the full dimensional width. Found to be inadequate for creating consistently acceptable sealing performance, those promoting and affecting lower leaks rates and emissions opt to use a gasket’s full width to determine gasket area and stress.
The full width of a spiral wound gasket is currently being determined in two different ways among industry participants. Most use the dimensioned outer diameter which includes the bead of winding wire that does not contact the flange surface. Some exclude the width of the bead. Inclusion or exclusion of the bead has a significant impact on gasket seating stress for sealing elements of narrow width as the width of the bead represents a large percentage of the overall dimensions.
In this paper, all three methods will be discussed focusing on gasket stresses for NPS calculated from the preferred method of full width comparing the inclusion and exclusion of the bead width.