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…

The most common modes of failure for vent lines is backpressure and thrust forces.
Backpressure failures can be from several causes:

• Inadequate calculation of the backpressure caused by the high flow rates. Vent system design pressure is often only designed for the maximum 10% backpressure that is required by ASME Code. However, it should be noted that the large flowrates from…

Vent systems are typically open to the atmosphere, so it’s easy to overlook that they must be designed to withstand significant internal pressure. The two primary sources of pressure within vent systems are: 1) backpressure from the flowing gas, and 2) internal deflagration/detonation.

The large flows of gas exiting relief devices and vents will create backpressure within the vent system…

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…

Yes, for all stacks. GH2 has a minimum prescriptive height of 10 ft. There is no minimum prescriptive height for LH2. However, 25 ft has been a best practice for the industry for years. Vent stack outlets that orient the release vertically help reduce the radiation exposure at ground level. Care must be taken to consider varying weather conditions, particularly wind, as well as surrounding…

Generally flaring is not recommended. Normally GH2 is not flared for most hydrogen equipment as the piping diameters are smaller. The largest stacks are the LH2 vent stacks on trailers and on tanks for the main safety valves are 3”. For GH2 systems the flare stacks are generally smaller in diameter. 

Flaring is a deliberate ignition of a hydrogen stream. If the hydrogen stream is to…

There are several levels of documents which can be used to assist with the design, sizing, selection, and installation of the pressure relief device settings for LH2 tanks. 

Pressure vessel design codes, such as the ASME Boiler and Pressure Vessel Code will provide minimum requirements for design of pressure vessels (including LH2 tanks), relief devices, and relief systems. However…

At least three of the ASME B31 piping codes are logical choices:

• ASME B31.1, Power Piping
• ASME B31.3, Process Piping
• ASME B31.12 Hydrogen Piping and Pipelines

Considerations for code selection include:

• Requirements imposed by the authority having jurisdiction, whether by direct reference or…

Safety codes globally have a requirement to provide a positive means to isolate energy sources and hazardous substances prior to performing maintenance. For gaseous hydrogen systems, methods such as a blind flange, a double block valve arrangement or a double block and bleed valve arrangement can provide that positive isolation.

Installing a blind flange requires breaking the supply line…

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…