Erection‎ > ‎Vent system design‎ > ‎

Standard and papers- vent line

1.API 520 1 Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries

For conventional relief valves connected to a flare header, there are several considerations that affect relief valve sizing and selection. The pressure relief valve discharge line and flare header must be designed so that the built-up back pressure does not exceed the allowable limits as specified in

3.3.3. In addition, the flare header system must be designed in order to insure that the superimposed back pressure, caused by  venting  or  relief  from another source, will not prevent relief valves from opening at a pressure adequate to protect equipment per the ASME or applicable code. Once the super- imposed,  built-up,  and  total  back  pressures  are  calculated based  on  a  pressure  drop  analysis  of  the  discharge  system, they  should  be  specified  on  the  data  sheet  for  the  pressure relief valve under consideration.

 2. IGC--Gaseous hydrogen stations, P3

Vents, including those of pressure relief devices, shall be arranged to discharge in a safe place in the open air so as to prevent impingement of escaping gas on to personnel or any structure. Vents should be piped individually, manifolding is not recommended. Vents shall not discharge where accumulation of hydrogen can occur, such as below the eaves of buildings.


3. IGC-Hydrogen transprotation pipelines, P20

The system must collect and route the hydrogen either individually or in manifolded headers to a vent stack  discharging  outdoors  in  a  location  and  direction  that  avoids  impingement  of  escaping  gas  on adjacent equipment, structures, or personnel. The exit should allow the hydrogen to flow easily out to atmosphere, minimize water ingress from the environment, discourage creatures from entering, and provide  quick  dissipation  of  the  hydrogen  into  the  atmosphere.  To  minimize  the  possibility  of  auto ignition when the hydrogen leaves the stack, it is recommended that the piping immediately upstream of the exit be made either of stainless steel or a non-sparking metallic material.  There  are  varying  opinions  about  the  need  for  and  efficacy  of  a  flame  arrestor  to  inhibit  backward propagation of a fire into the vent pipe. Similarly, purging of the vent line with an inert gas such as nitrogen may help to prevent auto ignition, but there are numerous reported instances where a purge was  ineffective.  Therefore,  this  document  makes  no  recommendation  either  way  at  this  time  other than to point out that flame arrestors and nitrogen purges do no harm.


4. NASA- Safety standard for hydrogen and hydrogen systems, P5-29

Pressure-relief devices discharge vents should not be connected to a common line when feasible.  The effect of the back pressure that may develop when valves operate should be considered when discharge lines are long or outlets of two or more valves having different relief set pressures are connected to a common line.  Discharges directly to the atmosphere should not impinge on other piping or equipment and should be directed away from platforms and other areas used by personnel because the discharge gas may ignite and burn. Reactions on the piping system because of actuation of pressure-relief devices should be considered, and adequate strength should be provided to withstand the reactions.


5. NFPA-50A Standard for Gaseous Hydrogen Systems at Consumer Sites, 2-2.2

Pressure relief devices shall be arranged to discharge upward and unobstructed to the open air in such a manner as to prevent any impingement of escaping gas upon the container, adjacent structures, or personnel. This requirement shall not apply to DOT specification containers having an internal volume of 2.0 ft3 (0.057 m3) or less.