the ASME standard for building pressure vessels is a process certification that signifies that the manufacturer followed best practices in welds, material sourcing (EXTREMELY IMPORTANT), rolling or forming, and of course, that the design was certified by the standards body.
the sum total of this is that the asme certified pressure vessel construction is the absolute minimum that an engineer designing a critical pressure/vacuum system will require in production. here is why: when a pressure vessel explodes, people die.
SO! there are plenty of tanks out there that invite you to fill them with pressurized gases or fluids. many of them are ok on their first few uses, or ok for the first month after production, but after repeated cycles of expansion and contraction, and potentially oxidization at weak points in the vessel, they will eventually let go. if you're lucky (for example, a contractor's compressor tank), the vessel will pop a few leaks and the end result will just be the compressor's motor locking up from overwork.
if you're unlucky, the vessel will basically become a grenade; it will explode and high velocity steel shrapnel will fire off in all directions. you will probably not see any evidence that the unlucky case is going to happen. often, this will happen while the vessel is pressurized (and not during a release or pressurization cycle). once a large enough piece of tank fires off, the resulting stress on the hull will disintegrate it.
so anyway, my rule of thumb is that for typical cast and mold applications with the materials that people here use, a 40-50psi cure pressure is pretty standard. to hold 40-60psi for the duration of a cast (30-60mins), i source at least 100psi asme rated pots. also, because these pots tend to sit at pressure for long periods of time, i only source stainless pots. finally, i don't source anything that could even possibly have chinese "steel" in it (the chinese metal market is an absolute mess).
finally, all seals, gaskets, and fittings are fluorinated, period. silicone cures give offgas caustic nasty stuff. a seal failing will have a similar effect to the catastrophic explosion above (possibly worse, actually).
so that's the pot! a lot of people ask about compressors and hosing (OH MY GOD SO IMPORTANT) as well. but yes, the pot? don't screw around. your life is not worth the hundred or so dollars separating a high quality certified pot from something that has a non-trivial chance of killing you.
oh, i should mention that vacuum pots are not things you should be screwing around with either. i have seen far too many acrylic topped soup pots that i can to recall. hey remember pressure pots turn into small grenades when they explode? turns out that vacuum pots do the same thing when they implode!
