How old is to old of a tanker?

I have seen some barrels that were built in the 70’s still used. They had air ride suspension and new fifth wheel plates and new valves, vapor recovery etc.
Propane/NG tanks even older.

 

Those old pressure vessels should have ASME "R" stamp plates for each re-build as this spec required ASME manufacture years before it came to the more common specification tankers.

There should be the original plate with the "U" stamp [if it existed yet] when the trailer was built along with the "R" stamp plate for each re-build +/or repair to the barrel, a historical record on the unit.

I remember when the current inspection requirements for 306/406, 307/407, 312/412 started with multiple questions regarding existing repairs, what was legal was was not.

At the same time older tanks on dealer lots tripled in price in a few months with the words 'passes inspections' added to the sale add...

I would bet quite a few of them are still working; especially any that were re-barreled in their lifetime.