Clarification (?) on DOT-412 Tanks Intended to Be Loaded by Vacuum

PHMSA has issued an interpretation on the regulatory requirements for a tank that is intended to be loaded by vacuum. It states that if a DOT 412 tank is designed to be loaded by vacuum, it must have a minimum external MAWP of 15 psig and must be constructed and certified to ASME Code. Notably absent from this interpration is clarification on whether that ASME certification needs to include certification for vacuum. One might think this is implied. However, it is perfectly normal in the Section VIII-1 world to design for full vacuum without rating/certifying the vessel for it. It’s kind of a matter of a different perspective that ASME has. Further, ASME specifically states its limit of scope at 15 psi. So is this in or out of scope? Furthermore, the case could be made that “full vacuum” is 14.7 psig, and therefore DEFINITELY implied out of scope for ASME. ASME allows the manufacturer to include the rating, but does not require it. Because of these questions, I find this interprtation kind of lacking in providing real clarity. Read it here.