From your question, I 'm assuming you'll be making or specifying the test vessel rather than contracting out the job. For a one-of-a-kind test, contracting will be less expensive.
First, you'd need to determine absolutelargest gadget you're ever going to want ot test: Almost assured, first time you "assume" that you'd never need to load something large than "xxx" inches, the next week you'll have a contract to build something "xxx+yyy" inches. 8<)
Get max size, max pressure, working fluid (clean water pure water so you don't to clean out problems when the seals or joints leak, low temp service or refrigerator cooling most likely if room temperature isn't correct for your test.)
Door size determines what you can load without re-assembling it inside. If you can manage the cost and floor space, put a joint all the way around at midpoint in the wall rather than a door and HP flange. Then (like the supper-guppy planes) you take the pressure vessel apart to "put" the piece inside, rather than siding it in via a small access hatch or manhole. (That's way more expensive though.)
Pieces are fairly small. The minimum require ment for the vessel is 4" diameter x 12" length. Do you know of any good contractors for this type of pressure vessel
