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NFPA 12 - Setpoint of PRV for CO2 Flooding System

Question asked by saintvida on Jan 12, 2020

Clause of NFPA 12 has the following requirement:

For high-pressure systems, the pressure relief devices shall operate at a pressure no less than 2400 psi (16,547 kPa) and no more than 3000 psi (20,864 kPa).


I have some background information and questions revolving around this NFPA 12 requirement:

  1. I work on offshore projects and we have vendors who supply CO2 total flooding systems for the machinery spaces on the facility. As a requsition requirement, we have specified to them that their system needs to comply to NFPA 12.
  2. On review of the vendor P&IDs, it was found that they have specified that the hydrotest pressure of their CO2 piping is 165 bar (ie. design pressure is 110 bar) and they have therefore specified the setpoint of the PRV for the CO2 system to be 100 bar. The setpoint makes sense considering that it should be set at a pressure not exceeding the design pressure of the system. 
  3. However, this sepoint of 100 bar will not be complying with Clause of NFPA 12. My main query is the reason behind why NFPA 12 has specified that the PRV shall be no less than 2400 psi (16547 kPa or 16.5 bar) as per Clause
  4. On further review of NFPA 12, I note that Clause of NFPA 12 requires that all flanged joints upstream of any stop valves be at least Class 600, but Clause of NFPA 12 requires that the setpoint of the pressure relief devices be no less than 2400 psi (16547 kPa). These two requirements appear to be contradictory as the Class 600 flanges are inadequate for the pressure of 2400 psi (16547 kPa).  
  5. I have reviewed the CO2 system on other# facilities from different vendors who obtained NFPA 12 compliance certification, and the system design pressure and PRV setpoints are all at 110 bar and 100 bar respectively. 


Appreciate any feedback on this question.