What ASME Standard(s) call out the length of a stud?  I recollect that somewhere a non-pressure retaining stud is measured end-to-end while a stud used in a pressure retaining application is measured first thread-to-first thread.you are talking about studs used on ASME flanges, then you can refer to ASME B16.5.  The stud lengths are listed in those tables with overall flange dimensions. Appendix D has instruction on how to calculate required bolt lengths. I noticed recently that ASTM F704 was a standard practice document for ASME B16.5 piping flanges. 
SME does not tell you what type of  Butterfly Valves  pipe to use...or what diameter ....or what the length of stud should be.
The ASME standards are not prescriptive as the API codes and standards are... I certainly hope that this should be obvious to any and all readers of these fora at this point in time

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