Since I began consulting I learned of something I thought I would never see… an ASME pressure vessel without a pressure relief device (PRD). Typically when I have come across one of these vessels I have gotten the “grandfather” or “its too small” justification. So let’s discuss these two items and see if they are actually legitimate exceptions to…
UG-125 GENERAL
(a) Other than unfired steam boilers, all pressure vessels within the scope of this Division, irrespective of size or pressure, shall be provided with overpressure protection in accordance with the requirements of UG-125 through UG-138, or with overpressure protection by system design in accordance with the requirements of UG-140, or a combination of the two.
Did you notice they mention “size” above? So if they state “irrespective of size” then how did size become an exception?
Have you ever heard of the 6-inch exception or maybe the 6-cubic ft exception?
DISCLAIMER: I am not a mechanical engineer nor a Professional Engineer (PE). This article is intended for safety professionals who have pressure vessels on their property which are managed by engineers. It is written to explain how these exceptions are intended to be applied and they have been IMPROPERLY applied so they can better ensure a safe workplace in regards to pressure vessel safety.