By N+1 I means one extra device over the capacity required for when there are no isolation valves. N+1 devices allows one isolation valve to be closed while maintaining full discharge capacity.
Hi,
Not a good habit to install isolation valve between nozzle and safety equipment. Forbidden in the companies I've been working for.
What is the point to have an isolation valve underneath a rupture disk?
Pierre
Found a copy of Yr 2021 ASME Section 13 on the net - there is nothing in non mandatory appendix B about N or N+1 relief valves and how stop valve may affect selection between N and N+1. It is entirely up to the Operating Company to choose N or N+1 and corresponding stop valve provisions to suit their needs. Refer also to the project specific relief valve sparing and isolation philosophy document for guidance.