Minimum Design Pressure

SP-1258

Pressure Vessels and Piping Systems are the main candidates for causing escalation in process systems. The critical consequences of a rupture (BLEVE) of a vessel or piping system are mainly accelerated fragments (missiles), fire ball and blast overpressure. One of the main concerns is missiles from a catastrophic failure of a pressure vessel or piping. However as the nature of mechanical failure of piping and pressure vessel are very different, vessel rupture could create missiles at very low pressures compared to a piping system. Risk of missiles is considerably reduced when rupture pressure of a vessel is about 4.5 barg. In contrast the pressure at burst of a pipe needs to be above 20 barg to have escalation risk of damage to neighbouring piping/equipment due to large deflections when the pipe bursts. 

 

API RP 521 

The pressure drop across either sonic or subsonic flare tips, the piping between the tip and the flare knockout
drum and staging valve (when present) shall be considered when specifying the flare knockout drum design
pressure. A minimum design gauge pressure of 345 kPa (50 psi) is suggested for knockout drums where
appropriate precautions are taken to ensure that the oxygen concentration is maintained below that required to
support combustion. 

NFPA 69 provides guidance on designing vessels for deflagration pressure containment and explosion prevention systems [126]. See 5.5.2 for effects of backpressure on PRDs. 

 

NFPA 69

Chapter 13 Deflagration Control by Pressure Containment

 

Energy Institute, Guidelines for The Design and Protection of Pressure Systems To Withstand Severe Fires. March 2003.