I think you're not getting any replies here since in the main, this forum section concentrates mainly on API/ASME Pressure Relief Valves in the oil and gas industries. I've not been asked to refer to CGA S 1.3 myself and from what I know, that is a different type of PRV requirement.

You may find some answers from the following link or repost your question in a more appropriate section of these forums. Good luck.
https://www.cganet.com/use-updated-cga-s-1-2-to-pr...

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

Re: CGA S-1.3

Bulk LIN cryogenic tanks of substantial volume almost always have both a relief valve and rupture disk. Relief valves are typically sized for NER, PB heat load, loss of vacuum, pump filling etc. Rupture disks are typically sized for the fire case set to 110% of MAWP at 800F. I would not recommend just putting in a rupture disk. In extended periods of low usage pressure will build up enough in the tank to open a PSV or blow a rupture disk. Doesn't make sense to lose the entire tank contents just because LIN hasn't been used for X days.

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Not making a decision is a decision in itself

Engineer M - The "secondary relief device" is for emergency scenarios such as fire exposure. I'm guessing that you don't have a copy of CGA S-1.3. If that's true, then i suggest you purchase a copy. It's important to get this detail right, and the standard will sufficiently explain the answers to your questions. I don't have a copy of this standard, but as I recall it gives you the option to use a rupture disk for the secondary device, but it doesn't require the use of a disk. You can choose to use a second PSV or a disk for the secondary device. If the contents are flammable or hazardous, then a PSV is a better design because it will re-close without emptying the entire contents of the container. i think this point is mentioned in the standard.

If the primary device has sufficient capacity for the emergency scenario, then is it still necessary to install a secondary relief device? You'll find that answer in the standard. If installation of a secondary device is mandatory it will say that one "shall" be installed or that one is "required". This is a prescriptive standard, so you don't have discretion to apply your own judgment to the requirements.