Any pressure vessel over 15psi is required to be manufactured to ASME Boiler and Pressure Vessel Code- so yes- all propane tanks are manufactured to ASME standards. I am the QA manager for a Cryogenic tank manufacturing facility. All of our inner tanks fall under ASME BPVC our outer tanks under AWS. All transportable tanks also require DOT approval, this is given to the manufacturer as a special permit
that is valid for 4 years. Manufacture has to reapply for these permits. If a company were to go out of business then the tanks would no longer be acceptable or recertifiable without some company requesting to take over the permit
. I deal with this every month for our beverage carbonation cylinders. ASME tanks will also have National Board numbers associated with them- each tank has it's own number associtated with the manufacturer and specific to that tank and serial
number. They have to be recertified because over time the welds and material can fatigue, causing leaks
or rupture. Pressure vessels are either cold stretched- filled with water- put under pressure and literally stretch the metal like a ballon or hydro tested- such is the case for propane tanks- they are also filled with water
and put under pressure but less pressure than in cold stretch. They are also mass spec'd- filled with helium and then mechanically sniffed for leaks- helium molecules are much smaller than water
or air and will find leaks
that hydro will not.
I realize this is more info than you requested but I thought you might want to know a little more about the tanks, how they are tested and why it is important. Tanks can and do explode and they can and do kill people. Testing the tanks can and does kill people- prior to my starting where I am one of the inspectors had his head
taken off during a hydro test.
My point- please do get your tanks tested- it may seem comical and un needed but it is very much a safety
issue. Yes you may never have problems but is it worth saving a couple bucks? These tanks are used regularly, they are under constant pressure, filled, emtpied, refilled time and again- this weakens joints and welds. There are also instances where it will be found years later that there are issues with valves over time- perhaps the casting wears, the membrane inside is found to wear out quicker than it should etc.
Please keep your tanks certified.