Purging can be accomplished in several ways including by using pressure cycles, sweeping, or vacuum. Sweeping is the least reliable but can be effective on simple pipe runs. In most cases, vent systems are open to the atmosphere and the ingress of air from the outlet is likely. However, the vent system should be designed to handle fire or explosion internally. This
generally is not…
It is not possible to define ignition potential by just velocity without more data (i.e. pressure, materials involved, direction of impact). Due to the multiple methods of developing an ignition source (friction, impact, electrical charge) and the low ignition energy, it is assumed that hydrogen in the air will ignite (between 4 -74%), as it does 30-40% of the time with no known ignition…
No, but it depends on the application. Nearly all vents less than 4” in size are not purged with N2. This is primarily due to: 1) large flows required to dilute hydrogen below the flammable range, 2) the cost of the nitrogen, 3) the potential blockage of the stack when being inserted a vent header/stack serving a liquid hydrogen system, 4) the potential for backpressure (depending on the…
There is no specific requirement not to vent liquid hydrogen from a vent system. Best practice would be to only vent gas from the top of the vessel to relieve pressure. If liquid must be vented, it should be vaporized first.
Note: It is very unusual to have LH2 flow from a liquid tank out the vent system, as the vent system is connected to the vapor space on the LH2 tanks and there…
I am not sure which picture you are referring to so I will attempt to answer.
If you are referring to the incident where a fire occurred and the vent system was damaged, then this may have been due to lack of proper supports and incomplete assembly of the test systems. In the past, vent systems were not pressure tested for strength but that is changing.
If you are talking…
There is no standard which specifically specifies the use of a flapper. A properly designed flapper should provide de minimus restriction to vent flow, yet still provides weather protection which allows for a vertical release of the vent stack flow, which is best from a dispersion and radiation perspective. Flappers are extensively used successfully and safely on nearly all liquid hydrogen…
All vent stacks/systems should be bonded and grounded to minimize ignition sources. Higher pressure streams from higher velocities have a greater risk of igniting for several reasons, including particle impingement. Adding mesh could create more impact points for particulate, which would increase the potential for ignition, but would not increase the probability of a DDT. Similarly, high flow…
Liquid hydrogen is rarely vented as a liquid. If liquid hydrogen is vented, there should be a means to ensure that it is fully vaporized. The vent systems for LH2 tanks are connected to the vapor space on the tanks to ensure in most instances, this occurs. Most vents from a liquid hydrogen system will vent gaseous hydrogen, but this gas, may still be as cold as -420 F. There are no code…
At least three of the ASME B31 piping codes are logical choices:
Considerations for code selection include:
The requirements of the code used for the original construction apply. The piping may meet the requirements of more than one code. In which case, the code used for changing the rating may be different than the original code of construction. In any case, the re-rated system should meet all of the requirements of the selected code. Note that if the original proof test of the system was…
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