Diameter of Skirt for Hemispherical Head

I don't think there is a standard for this; you may design it at your own option, so long as it meets strength requirements.

Thanks!!. However In my opinion mean diameter of hemispherical head shoud match with mean dia of skirt support if there is a sufficient clear gap between butt weld joint of shell to head and skirt support to head.Correct me if I am wrong.

Your reply that "there is no standard applicable" is valid also for selection of forged Y-ring?? OR Y-ring should be selected in certain cases like creep temp. range etc.

And if one decide to go for Y-ring then how to decide the dimensions of this Y-ring??

Is there any standard of any PMC available?? OR is there any standard procedure to dimention Y-ring??

This topic has been covered before: http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=hemispherical%20head&order=asc

I have seen vessel skirts anywhere from o.d. = shell o.d. down to stanchions of pipe. I think you are right to mention the distance between head-to-shell and head-to-skirt joints.

I am not familiar with the Y-ring terminology, and again I don't know of any standards for it. However, seismic considerations (e.g., overturning moment) may apply.