Suggest you design the flange as 'ring type integral', not 'ring type loose'. If you try 'ring type loose' you will have a problem defining the flange ID in COMPRESS since it will be smaller than the shell OD. For 'ring type integral' the design calculations are the same as Fig. 2-4 Sketch (8)thru (10a) but you will need to be sure the attachment weld meets the referenced requirements of Sketch(11). You may need to adjust the weld size in COMPRESS.