What industry codes and standards are used for leak testing of valves?

Any information is helpful along with any links to informative sites.

API(AMERICAN PETROLEUM INSTITUTE)598,MSS SP68,AWWA C-504,ANSI B16.34(IT GIVES THE TEMPERATURE VS PRESSURE RATING)

NOW,

For eg:-

you have a butterfly valve of 300 pressure class then how will you get the pressure rating,shell test pressure,seat test pressure?

you first confirm that the valve's pressure testing is as per API 598.Then go to ANSI B16.34 300# class to check the pressure rating for the particular material(body and disc).Under that you have diff. pressures for diff. temp. ranges,Confirm your medium's min to max.temperature then you can get the line pressure for your valve.Go back to API 598 and see the shell test rating(it will be 1.5 times the rated pressure)and seat test pressure(it will be 1.1 times the rated pressure).
There are lots of standards but the design always begins with the pressure class you want the valve to be.

The general understanding is that the ANSI Standard for Control valve leakage allows for a specific percentage of the rated valve capacity to pass through the seats when closed. The variation in standards is from 0.15 ml per minute (1 bubble) to 0.5% of rated valve capacity from Class VI to Class II, based on specific conditions of test.

You also may want to keep in mind the following. If a valve is tested and passes under the standard it is rated to lthat ANSI standard. But if you operate it in the field at out side the exact test conditions the valve will perform differently. But it is still rated to that shutoff class. Example:
A valve tested in the factory on Air or Nitrogen at 50 - 125