multiple pressure relief valves used on inlet natural gas line to a power plant

[MSPVIN]

the required capacity calls for 2 valves. can i increase the set pressure on the second valve?
the question is can i increase the set pressure to 16% non fire case or is the pipeline under DOT
and not pressure vessel code?

 

[The Obturator]

Set Pressure is usually based on the Maximum Allowable Working Pressure MAWP.
You don't advise why you would want to have a set pressure 16% higher. Are you maybe confusing this with overpressure?
Generally the PRV would follow ASME VIII Code Rules.
ASME VIII and API-520 Allow the staggering of the set pressure in such cases to prevent chatter.
1st valve is set at 100% MAWP and will have 16% overpressure.
2nd Valve will be set at 105% MAWP with 10% overpressure equalling total opening of first valve.

You may want to look at a single pilot operated PRV rather than 2 spring operated PRV's. The pilot valve will be able to handle a higher set pressure.

Please also note there is a dedicated safety relief valve forum.

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

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

 

[LittleInch]

You don't really give us anything to go on here in terms of where these valves are (downstream a pressure regulator?), what the design code is for you facility piping ( B31.1 or 31.3?), Design pressure / MAWP of whatever it is you're protecting and what your set pressures are.

As said above, when you have need for more than one valve then you need to stagger the set pressures to avoid chatter, but within limits.

If this is a pipeline inlet I'm very surprised if the volume flow for a fire case is more than a blocked discharge case.

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