Regarding time within which a shutdown valve of hydrocarbon export line should close.
The last time I checked, offshore regulations permitted up to 45 seconds to close a shutdown valve.  A throwdown number for valve closure is one second per inch body size.  Some valves over NPS 24 may require quick exhaust valves to meet beat the 45 second requirement.  My throwdown basis is spring-opposed ball valves.  The number is reasonable for butterfly valves although they should close more quickly.  If a faster closure is required you can work with the engineers to select larger actuators and tricked out pneumatic accessories.
Just check for hammer.  On fail close valve, I buy several different sinter bronze or aluminum vent filters.  Each one has its own Cv and find the one that works for the valve.

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