It has grown tiresome, but it remains a teachable moment, to debate “engineers” who want part of ASME/NBIC to be the gospel and other parts not so much. The ammonia refrigeration industry just can’t seem to grasp the critical need in their “Common PRV Header Design” v.s. having more “holes in the roof” (as they like to point out). And today, I got word a technician was performing their 5-year PRV maintenance with the refrigeration system in full operation. A compressor RV lifted, discharged into the shared PRV header, and gassed the employee who needed ALS medical care. He would have been flown to a trauma center, had the weather permitted. No LOTO in place for these “line breaks”, but more importantly, there is NO WAY to isolate each RV from the common header such that LOTO can be applied. This is a “newer” process, built in 2019/2020 and this was the first time the RVs needed to be changed out. In my PHA/Engineering Code Analysis, it was suggested (in 2017) that if the process was going to utilize a common header then ASME/NBIC requirements should be considered in this design. The “contractor” hired to design and build the process stated he had never done it like that before and “in fact, it’s illegal”, so the business took the easy path and built the common header with no means to isolate each PRV. In other words, the PHA recommendation was to shut down the process and perform the maintenance since there was no mention of isolation. The business did neither and now they are worried about my PHA recommendation(s) creating a citation path – how about worrying about the worker you put into ICU?
So I am providing the latest from the NBIC Part 4 regarding when, where, and how to use “intervening valves” in PRV path(s) so that maintenance on these PRVs can be performed safely. And yes, the code calls out the ammonia refrigeration common PRV header design as one such design where an intervening valve is not only allowed; it is called for.
(Emphasis by me)