Thanks MJCronin for the reply.
340 psig at 115F is the calculated pressure of my hydrocarbon stuff. Too bad the propylene cylinders will not fit.
First, I need a small, like under 1,000L, cylinder for development stage, then a larger one, like 4-8K litres. I hope to find ready avalable cylinders as making a special one(s) is not economically feasible.