Minimum Wall Thickness

Please refer to ASME Sec. VIII Div. 1 (or other suitable pressure vessel code)

You apparently (obviously) do not have a copy - it would be VERY EASY to supply you an answer to your question - however, you would miss out on A LOT of the other details that are required to safely design and construct a pressure vessel.

(A little knowledge is a dangerous thing)

I hope I am nowhere near this thing when it first goes into service. Why not engage the services of a design engineer who is well experienced in the design of vessels such as you are looking for?

Notwithstanding the potential for a disaster here, what about the old adage 'if you don't have the resources to do it right the first time, where do you think you will get them to redo it when it fails'?

I've had Wheeler Tank Manufacturing, Inc. in Sioux Falls, SD fabricate pressure vessels for me before. The vessels are built to code and stamped, and Wheeler has fairly resonable prices.