I'll try to deal with these in turn,
1) (Valvesmex) ANSI / ASA SPECIFICATIONS - ANSI replaced ASA about 20 years ago, some people still refer to ASA when quoting for valves or fittings. However for correctness ANSI or ASME should be quoted.
ANSI - American National Standards Institute
ASME - American Society of Mechanical Engineers
ASA - American Standards Association
2) (Rehmani) Simple answer, refer to ASME/ANSI B16 Piping Component Standards, this is the dimensional code for piping components, also gives geometric, material make-up and strength of items.
3) (ALAB-1) As mentioned above ASME/ANSI B16 refers to Piping Component Standards,
"B16.11 = Forged Fittings, Socket Welding & Threaded"
"B16.25 = Buttweld Ends"
"B16.34 = Valves-Flanged, Threaded & Welding Ends"
In a Piping Specification when referring to a valve with a buttweld end, the schedule of the pipe is usually noted, i.e. Sch. 40 Plain End to 2" / Bevelled End 2.5" & above.