The Panel recommends performing a pressure test at 110% of design pressure. This requirement should be applied to all systems regardless of construction type since the intent is to ensure pressure integrity and proper installation. All fitting types have modes of failure during installation. For example, there are numerous examples where compression fittings have had ferrules installed…

The HSP recommends against the use of glycols for pressure tests due to the difficulty of adequately removing all glycol that might be left in a system after a hydrotest. The HSP recommends a pneumatic test at 110% of the system maximum allowable working pressure (MAWP), which is acceptable by code. Due to an increased danger with pneumatics vs hydrotesting, establish a pressure test zone for…

NFPA 2 provides Tables in Chapters 7 and 8 that specify the hazardous area classifications surrounding vent stack outlets. These are based on typical vent systems and flows, but are only applicable for smaller systems. The designer of a vent system should apply the principles of documents such as IEC 60079-10-1 (also required by NFPA 2) or NFPA 497 to evaluate larger vent releases where the…

Guidance for location of vent stacks is provided by NFPA 2, Hydrogen Technologies Code, which also references CGA G5.5, Hydrogen Vent Systems, for additional guidance. Minimum distances to vent stack outlets should be determined from dispersion and radiation analyses. The height of the vent stack and orientation of the release will affect the minimum separation distance.

Dispersion and radiation analysis should be conducted to ensure that the hydrogen cloud will not interfere with the flight path of aircraft. In addition, there may be maximum height requirements due to airport requirements depending on the location of the stack.

Hydrogen affects the mechanical properties of most materials. For example, hydrogen reduces the
fracture toughness and increases the fatigue crack growth rate in steels. There is a significant amount of
research, analytical work, and codes and standards development being undertaken to improve our
understanding of how these materials can be utilized in pipelines. The results of the…

Because cast irons are relatively brittle materials, they should generally be avoided in industrial and
transmission pipeline applications. In low pressure applications like residential distribution piping
systems, the use of cast irons is probably acceptable.

Acceptability of materials is highly dependent on the specific application. Applied stress levels, exposure to contaminants, the operating temperature, the partial pressure, and number and magnitude of material stress cycles are some of the factors that affect material selection. Guidance is provided within documents such as ISO 11114, Gas cylinders - Compatibility of cylinder and valve…

Hydrogen has been transported safely through pipelines for over 50 years. There are dozens of pipeline networks in safe operation globally, with several individual networks that approach up to 1000 miles. 

Significant testing and some demonstration projects are underway to ensure safety. Some of the aspects under investigation include compatibility of the pipe and other materials,…

Documents such as NFPA 2, Hydrogen Technologies Code, and the International Fire Code have quantity thresholds that differentiate requirements for the design of systems and enclosures. However, even the smaller quantities present a hazard under specific conditions, especially for systems that have the potential to release hydrogen into a confined or unvented space. Good engineering judgement…