Also, as stated above, ASME B16.9 is not the code, but the standard for "Factory-Made Wrought Buttwelding Fittings". But that is not the standard for flanges. Normally, the flanges would fall under ASME B16.5 "Pipe Flanges & Flanged Fittings" for up to 24" but since your Client is recommending A694 Gr. F60, this should fall under the MSS SP-44 "Steel Pipeline Flanges" standard because A694 is not a listed material under B16.5.
Here is a link to a previous post to help with some of the differences:
Again, the code will need to be verified with the owner, and could be any one of the following:
ASME B31.3 "Process Piping"
ASME B31.4 "Pipeline Transportation for Liquids & Slurries"
ASME B31.8 "Gas Trasmission & Distribution Piping Systems" (likely)
All of these codes have their own requirements and most are quite extensive to read through. And since you are unfamiliar with the codes, it's best to leave it to someone else. I do appreciate the fact that you admit that you are not familiar with the ASTM or ASME codes & standards, but as everyone has stated above, you need to find a trained and qualified individual or separate firm to do the engineering and design of the piping. There are many factors that go into determining piping size, wall thicknesses, classes, etc., and this is not something you should just be guessing at and trying to figure out yourself. That's how people get hurt.
Good luck to you.