Hydrogen is finding some footing for wider use as a fuel these days, and I have seen a significant increase in inquiries from existing and new clients about process safety for H2 storage and use. I always follow Chapter 700 of the International Gas Code as my baseline code requirements and then move into NFPA 2 for a more detailed analysis of the process. In this article, we will cover the pressure and leak testing of H2 piping, as many contractors are not following this or ASME B31.12 for this safety-critical step in the design and construction of H2 piping.
705.1 General.
Prior to acceptance and initial operation, all piping installations shall be inspected and pressure tested to determine that the materials, design, fabrication ,and installation practices comply with the requirements of this code.
705.2 Inspections.
Inspections shall consist of:
- a visual examination of the entire piping system installation and
- a pressure test.
Hydrogen piping systems shall be inspected in accordance with this code. Inspection methods, such as those outlined in ASME B31.12, shall be permitted where specified by the design engineer and approved by the code official. Inspections shall be conducted or verified by the code official PRIOR to system operation.
705.3 Pressure tests.
A hydrostatic or pneumatic leak test shall be performed. Testing of hydrogen piping systems shall utilize testing procedures identified in ASME B31.12 or other approved methods, provided that the testing is performed in accordance with the minimum provisions specified in Sections 705.3.1 through 705.4.1.
705.3.1 Hydrostatic leak tests.
The hydrostatic test pressure shall be not less than one-and-one-half times the maximum working pressure, and not less than 100 psig (689.5 kPa gauge).
705.3.2 Pneumatic leak tests.
The pneumatic test pressure shall be not less than one-and-one-half times the maximum working pressure for systems less than 125 psig and not less than 5 psig whichever is greater.
For working pressures at or above 125 psig, the pneumatic test pressure shall be not less than 110% of the maximum working pressure.
705.3.3 Test limits.
Where the test pressure exceeds 125 psig, the test pressure shall not exceed a value that produces hoop stress in the piping greater than 50 percent of the specified minimum yield strength of the pipe.
705.3.4 Test medium.
Deionized water shall be utilized to perform hydrostatic pressure testing and shall be obtained from a potable source.
The medium utilized to perform pneumatic pressure testing shall be air, nitrogen, carbon dioxide, or an inert gas; oxygen shall not be used.
705.3.5 Test duration.
The minimum test duration shall be 1/2 hour. The test duration shall be not less than 1/2 hour for every 500 cubic feet (14.2 m3) of pipe volume or fraction thereof. For piping systems with a volume greater than 24,000 cubic feet (680 m3), the test duration shall not exceed 24 hours. The test pressure required in Sections 705.3.1 and 705.3.2 shall be maintained for the entire duration of the test.
705.3.6 Test gauges.
Gauges used for testing shall be as follows:
- Tests requiring a pressure of 10 psig or less shall utilize a testing gauge having increments of 0.10 psi or less.
- Tests requiring a pressure greater than 10 psig but less than or equal to 100 psig shall utilize a testing gauge having increments of 1 psi or less.
- Tests requiring a pressure greater than 100 psig shall utilize a testing gauge having increments of 2 psi or less.
Exception: Measuring devices having an equivalent level of accuracy and resolution shall be permitted where specified by the design engineer and approved by the code official.
705.3.7 Test preparation.
Pipe joints, including welds, shall be left exposed for examination during the test.
705.3.7.1 Expansion joints.
Expansion joints shall be provided with temporary restraints, if required, for the additional thrust load under test.
705.3.7.2 Equipment disconnection.
Where the piping system is connected to appliances, equipment, or components designed for operating pressures of less than the test pressure, such appliances, equipment, and components shall be isolated from the piping system by disconnecting them and capping the outlet(s).
705.3.7.3 Equipment isolation.
Where the piping system is connected to appliances, equipment, or components designed for operating pressures equal to or greater than the test pressure, such appliances, equipment, and components shall be isolated from the piping system by closing the individual appliance, equipment, or component shutoff valve(s).
705.4 Detection of leaks and defects.
The piping system shall withstand the test pressure and test duration specified without showing any evidence of leakage or other defects. Any reduction in test pressure as indicated by the pressure gauges shall indicate a leak within the system. Piping systems shall not be approved unless the reduction in pressure is attributed to some other cause.
705.4.1 Corrections.
Where leakage or other defects are identified, the affected portions of the piping system shall be repaired and retested.