Pressure vessel ratings are a huge area of engineering, and various codes will literally fill libraries. Depending on the end use, design basis, degree and types of testing, "max" (hydrostatic test) pressure can often be 2:1 or 4:1 (or other ratio) of the rated working pressure. Most companies are smart enough to NOT show the test pressure in their marketing info. to home consumers, because there will always be some yahoos out there who will see that and then think it's safe to operate beyond the working pressure, up to (or even above!) the test pressure. I've also seen people who bypass the PRV (or place a valve between the vessel and the PRV) on their conicals for various reasons. Bad idea. The "maximum working (or operating) pressure" and PRV are there for a very good reason. You really don't want to operate beyond the working pressure even though you can, and probably would, get away with it. Probably, but then maybe you get busy with something else and (if the PRV has been removed or defeated) the pressure continues to increase. Yeah, it's a legal and a safety issue. I promise you if the conical has much gas in it, and it "let's go", you REALLY don't want to be there when it does.