Applicability of the Taylor Forge Method for Flange Design to High Pressure Bolted Joint Flanges With Lens Ring Gaskets

The design-by-formula methodology used by the ASME Code for bolted-flange joints offers no guidance for the determination of flange stresses for high-pressure applications. More specifically, it offers no guidance for bolted joint connections using lens ring gaskets. The Taylor Forge Method adopted by the Code in Appendix 2 of Division 1 and Paragraph 4.16 of Division 2 has well known limitations, most notably: (a) the joint elements are modeled using simplified plate and shell theory and neglecting pressure inflation effects, (b) the nozzle-neck axial pressure stress is omitted in the calculation of the longitudinal hub stress, and (c) the pressure end load H_D is assumed to act through the mid-thickness of the large end of the hub. In addition, the so called maintenance factor m, and the design seating stress y, are not defined for this type of partially self-sealing gasket. Lens ring gaskets are line contact seals based on the unsupported area principle. According to this principle, the internal pressure acting on the uncompensated lateral surface forces the lens towards the edge of the cone increasing the load on its sealing surfaces. The calculation of the forces and moment exerted on the flange as a result of this loading is also not considered in the methodology used by the ASME Code. In this article a study of the state of stresses for High Pressure Bolted Joint Flanges with Lens Ring Gaskets is carried out by means of Finite Element Analysis. The results of the numerical analysis are compared to those obtained by applying the formulae in Appendix 2 of ASME VIII Division 1 in order to determine to which extent these analytical expressions can be used while preserving the safety margins seen for regular flanges.