Compressed Gas Piping System Components

Fittings must be mechanically sound, leak free, and suitable for hydrogen services and for the specific operating conditions. Welded fittings are usually preferred for joints in hydrogen piping systems because welding reduces the potential for leaks compared to mechanical fittings.

Regardless of type, all fittings must be made of hydrogen-tolerant materials and designed according to the specific pressure and temperature conditions under which they will be used and compliance with the appropriate codes and standards should be documented. Documentation of compliance will be required for any type approval conducted by a Nationally Recognized Testing Laboratory (NRTL) (test laboratory such as UL) and by local officials permitting a hydrogen project.

Valves are required mainly for on/off applications and occasionally for throttling flow. For example, valves are needed for:

• Shutoff on storage container outlets, except for pressure relief devices. In some cases, fast closing valves may be needed.
• Isolation valves for emergency shutoffs.
• Isolation valves to isolate components for maintenance.
• Isolation valves needed for purging piping and equipment.

Valves must be suitable for hydrogen service and the specific operating conditions.

Regardless of type, all components of valves must be made of hydrogen-tolerant materials and designed according to the specific pressure and temperature conditions under which they will be used and compliance with the appropriate codes and standards should be documented. For example, some austenitic stainless-steel valves have stems that are made from martensitic stainless steel. Austenitic stainless steel is generally considered acceptable for hydrogen service, whereas martensitic stainless steel is not. Documentation of compliance will be required for any type approval conducted by an NRTL (test laboratory such as UL) and by local officials permitting a hydrogen project.

Excess flow valves may be required per NFPA 55 Compressed Gases and Cryogenic Fluids.

Excess flow valves are mechanical devices that shut off flow at a preset maximum flow for specific pressures and temperatures and are intended to detect a large leak such as a broken pipe or ruptured hose and stop flow.

After closing, a manual reset is typically required.

Excess flow valves are suitable for applications with known low flow rates during normal operation where they can clearly identify a situation with flow above an acceptable level.

Because they are vulnerable to abuse and accidental releases of hydrogen, use of hoses should be minimized and hoses should be protected from physical damage as much as possible. 

Hoses may be metallic or nonmetallic but, in any case, need to be conductive for grounding. Hoses that have a flexible metal covering are more resistant to abrasion and provide a level of fire resistance.

All hose materials must be hydrogen-tolerant and hoses must be designed according to the specific pressure and temperature conditions under which they will be used and compliance with the appropriate codes and standards should be documented.

Hoses should be inspected at least annually and replaced if any wear or damage is observed.

Regardless of damage, hoses should be replaced no less frequently than every 3 years.