Appendix II of ASME Section VIII, Division 1, 1977 Edition contains rules for the design of flanges where the gasket is located inside the bolt circle and there is no contact between the flanges comprising an assembly outside the bolt circle. Further, the hub or nozzle is located at the bore of the flange. Hereafter in this paper such flanges will be denoted as "conventional" flanges.

Rules are being added to Appendix II to cover the design of reverse flanges where the shell is attached to the outside diameter and there is no contact between the flanges of an assembly outside the bolt circle. Fig. 1 illustrates a typical reverse flange. The design procedure for reverse flanges was developed using the basic rules and procedures applicable to conventional flanges modified as necessary to account for the difference in behavior of such flanges. Basically, the modifications consist of redefining certain terms and the introduction of factors to convert T, U and Y to Tr, Ur, and Yr, where the subscript "r" indicates that the term is to be used for designing reverse flanges. In each instance the factor is a simple function of K, or more specifically, the ratio of the outside diameter to the bore diameter. Additionally, dr, er, ho and Lr are defined; these are the reverse flange counterparts of d, e, ho, L. Finally, an equation was added for calculating the tangential stress at the bore since this is often the controlling stress in a reverse flange.

The purpose of this paper is to provide a permanent record of the development of the ASME Code rules for reverse flanges.