ASTM E 186 for castings upto 2in wall thickness and ASTM E446 for wall thickness from 2in to 4.5 in wall thickness cover the acceptance standards for steel castings. Also there is a specification drafted by SFSA for acceptance of valve castings  titled

"Steel castings for controlled qualty level, general industrial steel castings grades for valves, visual surface inspection and scheduled radiographic inspection."

  http://www.sfsa.org/sfsa/pubs/rss/40T-78.pdf

 Hope this helps. Also please remember a basic fact that a radiographically accepted  valve body casting need not be hydrostatically sound. Please draft your acceptance standard keeping this aspect laying equal emphasis for hydrostatic testing procedures.

Where valves are concerned than ASME B16.34 gives NDE requirements for special class valves. This NDE can also be applied to standard valves. The only problem with B16.34 is that it does not cover all valve configurations and some of the drawings can be open to interpretation, it is however a very good starting point. There was also a new EN standard 12516 which was in draft format and was to include the valve configurations of B16.34 and other types not included e.g. Ball Valves.

If you need further info. please let me know.