Not many know this dirty little secret about overpressure protection on ASME-coded vessels (formerly called "code case 2211"), but I will let the cat out of the bag... Not all ASME pressure vessels have to have a pressure relief device, and I am not talking about those very small vessels, but any size vessel. No, I am not crazy, it is a fact. Since 1996 ASME has allowed this practice by issuing "Code Case 2211". Code Case 2211 was first approved in 1996 and reaffirmed until it became UG-140 in 2008. I am in NO WAY advocating this practice, but it is an option and is used in certain processes where relief devices can be easily compromised due to relieving events. This article is to inform those who want to know more about this practice and to ensure that those who are already utilizing UG-140 have all the required documentation on hand.
In NO WAY does ASME want this to be the first choice of users, but rather an option in some very specific circumstances. But in some applications, the use of pressure relief devices may be impractical. Some situations may include: