Section XIII Nonmandatory Appendix B - N+1 devices

[KevinNZ]

When there are isolation valves under burst disks. Is N+1 disks always required? Are there circumstances where N devices is allowed?

 

[The Obturator]

Where are you getting N+1 from? Please be more specific, there is no mention of N+1 in Appendix B that I can see.

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the ASME/API used term ***

 

[KevinNZ]

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.

 

[shvet]

1 or 1+1 PRDs does not depend on upstream isolation valves.

 

[The Obturator]

My question was, where in ASME XIII Appendix B, is the reference for N+1 written?

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the ASME/API used term ***

 

[pierreick]

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

 

[georgeverghese]

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.