An improved diaphragm design for use with a gasket in a pressure vessel manway opening to prevent leakage of a pressurized fluid was developed by B&W Canada. The design was developed for high pressure typical of conditions in the primary side of a PWR steam generators. The sealing is achieved by a spiral-wound graphite filled gasket which is confined in a separate diaphragm groove. The diaphragm has an internal radial groove which uses strong spring back and the pressure of the fluid to increase and maintain the gasket seating load. As a result, this design provides a self-energizing joint which can accommodate changes in gasket contact pressure due to cover rotation, stud elongation and change in fluid pressure and temperature. Finite Element (FE) Analysis indicates that a more uniform distribution of gasket contact pressure along the radial gasket width is obtained and thus the sealing performance of the gasket is improved.

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