Improved convoluted flanges

Improved convoluted flange including one embodiment having a metal inset in a polymer casing in which the inset has a convoluted configuration similar to the outer convoluted configuration of the casing and another embodiment of a convoluted, slip-on, welding flange for welding to a pipe having a cross sectional, convoluted contour that is configured using stress analysis to shift the effective loading of connecting bolts from the centerline of the bolt holes in the flange to a locus closer to the pipe to which the flange is welded.

This invention relates to improvements in the design of piping flanges and relates to the use of stress analysis to assist in the design of optimum configurations for a flange coupler as described in my prior patent, U.S. Pat. No. 5,413,389 issued May 9, 1995 and entitled, "Cast Convoluted Piping Flange". In the referenced patent a piping flange was described having a convoluted design with a transition in thickness from an outer rim to an inner rim of the flange. The convoluted design provided the rigidity or stiffness necessary to insure a uniform coupling face for uniform deformation of a gasket or seal, while minimizing the weight of the flange by eliminating unnecessary material.

The convoluted flanges and flange couplers of the type described in the reference patent are successful in accomplishing the objectives enumerated. Furthermore, the technique of computer aided stress analysis in the design of piping flanges has led to further improvements in the configuration of flanges that address the issue of stresses transmitted to the pipe, and in the design and construction of composite material flanges.

With regard to the latter, my prior patent, U.S. Pat. No. 4,458,924 issued Jul. 10, 1984, entitled, "Bimetal Flange Connector", describes a bimetal flange that utilizes a hub of a first metal bonded to a rim of a second metal. The concept of a composite flange of two materials and the use of a recess to reduce weight and optimize stress distribution is described in the referenced bimetal flange patent.

The subject invention includes certain of the features of the devices in the referenced patents. The advantage of computer aided stress analysis provides embodiments of piping flanges that fully consider the effect of the flange configuration in transmitting stresses to the pipe as well as efficiently distributing stresses in the flange itself.

The improved piping flanges of this invention incorporate flange configurations that optimize the stress distribution from the connecting bolts while minimizing the weight of the flange.

In one embodiment, a convoluted flange inset is encapsulated in a polypropylene casing to form a strong, yet light weight flange that is particularly suitable for corrosive environments. The polypropylene casing protects the metal inset from caustic or acidic environments and is adapted for connecting plastic or coated piping as well as conventional metal piping.

In other embodiments, the convoluted flange design is optimized for use primarily as a slip-on welding flange designed to minimize the transmission of torsional stresses at the neck of the flange to the pipe through the weld. To accomplish this design objective, the resultant locus of bolt-load, pressure distribution is shifted from the radial location of the conventional ASME flange to a concentrically inward locus on the improved flange. This shifts the moment arm to the fulcrum locus at the flange face, thereby reducing the magnitude of leveraged forces transmitted to the neck, that are ultimately transmitted to the weld joint and hence to the pipe.

Stresses in the wall of a pipe are generated by the pressure of fluid in the pipe. The bolt-load stresses transmitted to the pipe by the neck weld are cumulative to the stresses generated by the internal fluid pressures. These stresses can easily reach the failure point of the pipe if not controlled. As a design criteria, the pipe flange weldment should withstand 200% of the operational pressure yet maintain a peak stress level at 40% of the yield strength of the coupling material.

The result of the analytical design for the slip-on flange can be applied to other convoluted flange designs, such as a welding neck flange or any flange where it is desired or advantageous to optimize the reduction of material in the flange or to shift the load point from a locus of the centerline of bolt holes to a locus concentrically closer to the centerline of the pipe.