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.