Compressed Gas Piping Systems
Recommendations for compressed gas piping systems include the following:
- Piping systems should conform to a recognized code such as ASME B31.1 Power Piping, ASME B31.3 Process Piping, or ASME B31.12 Hydrogen Piping and Pipelines.
- To prevent leaks when exposed to an external fire, the piping system should be fire resistant.
- The piping material should be selected for robustness, low permeability, and fire resistance. The material chosen should be specifically rated or approved for use with hydrogen at the planned pressure.
- Optimum material selection depends on:
- The temperature range
- The pressure
- Purity and cleaning requirements
- Installation factors (structure, environment)
- In most instances, austenitic stainless steels such as Type 304 or 316 are satisfactory for end use applications.
- See Material Compatibility for more information regarding material selection.
- Design of the piping system should consider ways to facilitate internally cleaning the piping when needed.
- Considerations for underground piping include:
- External corrosion
- Protection from inadvertent excavation
- Preventing hydrogen from entering an enclosed space if a leak occurs
- Using only welded joints
- Alternates to direct burial of piping include:
- Route the pipe in open trenches with removable grating so that it can be inspected and maintained.
- When pipe can be routed without any mechanical joints, place the pipe in a corrosion resistant sleeve that is open at both ends.
- Piping should not be left open to the atmosphere. Openings should be plugged, capped, or flanged or routed to a vent stack.
- To assure dispersion of small leaks, piping should be routed outdoors whenever possible.
- Piping should be routed so that it is:
- Not covered by wall, floor, or ceiling finishes
- Readily available for visual inspection and leak detection, and
- Protected from physical damage
- The hydrogen system should have the necessary connections for isolating, venting, purging and leak testing, along with those needed to prepare the equipment for maintenance.
- When part of the system will remain operational while another part needs work, consider a double block and bleed arrangement to isolate active parts of the system from equipment being maintained and to facilitate purging.
Regardless of system design, a procedure for purging any piping to remove all air, moisture, or oxidizing gas or substance must be developed and documented.