Requirements for Equipment
When performing maintenance and repairs to any equipment, make sure replacement components are the correct ones. If identical parts from the original manufacturer cannot be used, then verifying that replacement parts are made of acceptable materials is extremely important for hydrogen applications. Use of a positive material identification (PMI) program is recommended for equipment (See Note below.) in hydrogen service. Verification of metal alloys using either x-ray fluorescence or spark emission spectrography is accurate, inexpensive, and fast. For metallic components to be used in hydrogen service, consideration should be given to establishing a program for positive material identification like that described in API RP 578.
Because hydrogen storage vessels generally have a large consequence of failure to workers and facilities, proper regulatory requirements, and industry standards for maintenance of hydrogen storage vessels including periodic inspection, examination, and recertification must be followed.
In the USA, several different codes apply to hydrogen storage vessels depending on the type of vessel and the jurisdiction.
- Fixed vessels – ASME Boiler and Pressure Vessel Codes (BPVC), Compressed Gas Association (CGA), and the National Fire Protection Association (NFPA)
- Mobile vessels – Title 49 of the Code of Federal Regulations (CFR), which covers the transport of hazardous materials under the Department of Transportation (DOT)
Vessels should be subjected to non-destructive examination at planned intervals.
- Potential problems with metal vessels include enhanced fatigue crack growth and hydrogen embrittlement due to cycling at high pressures. See Material Compatibility
- Pressure vessels may be required to be pressure tested periodically.
- Recommended best practices are as follows:
- Follow the code that governs your vessel. The requirements are different, e.g., DOT requires retesting, while ASME does not.
- Refer to your state and local regulations for specific inspection requirements for pressure vessels
- Follow the vessel manufacturer’s recommendations
- If leaking gas is heard, or damage to the vessels is observed (dents, cracks, etc.), then immediately remove the vessel from service and begin the appropriate maintenance
Instruments such as leak detectors, flame detectors, and flow controllers should be tested and recalibrated or replaced on a regular basis using the guidance provided by the manufacturer.
Machinery such as compressors and vacuum pumps should be maintained on a regular basis using the guidance provided by the manufacturer.
Note: As used in this section, “equipment” is an all-inclusive term that includes piping, instruments, and controls as well as those hydrogen system components commonly known as equipment.