Plugging is a concern before, during, and after a release. Prior to the release, water may accumulate in the vent system from weather conditions (rain, snow, etc.) or from condensation, particularly if there is intermittent flow which causes the stack to get cold. This water can freeze due to ambient conditions prior to a release, thereby blocking the stack. It is also possible for
other…

The potential of an explosive atmosphere is inherent with any vent system and must be addressed through adequate design. Purging for most vent stacks is impractical due to availability or cost. In addition, and particularly for LH2 systems, the purge gas can cause potential safety issues. The primary way that explosive atmospheres are addressed is through ensuring that the design of the vent…

Yes, and this is frequently done. A redundant vent stack might have its own independent redundant relief devices, or it may take the form of a secondary stack attached to the same devices. When a secondary vent stack is installed in parallel using the same relief devices, there often will be a means to isolate the second stack, such as a rupture disc, from the first except in
emergencies.…

CGA G-5.5 provides several options for vent stack outlets but not all options, nor does it tell when one outlet type is better than another design.

Figure 7, is one design, but in my opinion, not the best design. For instance, for warm gas, typical no-flow, normal scenarios (like a rupture disc on a vent system), Figure 5, a capped vent pipe is the simplest.

My preference depending…

This decision would depend on the system design, system operation, and a hazard assessment. Likely it would be better to run all hydrogen vents to a common vent or flare system, but this might also restrict the ability to isolate smaller sections for maintenance. 

The distances provided are minimums. While they might be sufficient for most vents from small systems, larger vents will require both a dispersion and radiation analysis to determine the height needed.

Nearly all hydrogen storage tanks and hydrogen storage systems will need some type of pressure relief system to protect the vessels from overpressure. If there are pressure relief devices, some means to vent the hydrogen to a safe location will be needed. An exception to this is hydrogen cylinders due to their relief device type (lead-backed rupture discs (CG-4/5) and
the need to transport…

We are not certain what an inverted vent top is. If this means the hydrogen flow is pointed downward in any way towards grade, then yes it must be avoided. Less dangerous vent gases can be pointed downward, especially those that mix with air rapidly (nitrogen/oxygen/argon). Regardless, reaction forces must be taken into account for any relief valve activation or flow

There are many designs of storage systems where multiple vessels might be needed to obtain the required storage quantity. Regulations differ between vessels and modules which are intended for stationary or transportation purposes. Similarly, there are differences in codes globally. The issues of requiring shutoff valves on individual vessels and requiring TPRD’s are linked since generally…

Welded joints are always best, but they cannot always be used as a connection to tanks and tubes, as mechanical joints are needed for maintenance. Supports for the reaction forces can help ensure the mechanical joints in the piping does not pull apart. 

If large diameter or thick-walled tube is installed with compression fittings, the use of hydraulic swaging is recommended.

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