This is another very common question for those getting into PSM/RMP, where their RAGAGEP requires the piping to be protected from a “blocked-in liquid” scenario, such as Liquefied Petroleum Gas (LPG). Many realize the dilemma only after installing their HRVs/TRVs; unfortunately, they have to go back and remove these relief valves to perform the “Pressure Test” (e.g., the first phase of a leak test). In some designs, the relief valves could be ISOLATED from the testing boundary, but that is a rare occasion for most facilities.
For example, my LPG piping is Sch 40 A106-B, with a 350 psig MAWP…
If 350 psig is actually the B31.3 design pressure, the basic hydrostatic test requirement is: 1.5 × 350 = 525 psig minimum
B31.3 §345.4.2 requires at least 1.5 times design pressure, with an additional allowable-stress adjustment when the design temperature is higher than the test temperature.
And this creates the HRV problem.
If we are using NFPA 58 as our RAGAGEP (and we should be!), the HRVs are required to be: 400–500 psig for a system designed to operate at ≤350 psig.
Therefore, we cannot leave a 400- or 500-psig HRV exposed to a 525-psig B31.3 hydrotest.
That’s not a problem with the piping design. It means the HRVs have to be handled as test-excluded components.
B31.3 §345.3.4 specifically says equipment that isn’t to be tested must be disconnected or isolated by blinds or other means; a valve can be used if the valve and closure mechanism are suitable for the test pressure.
We would hydrotest the piping to the B31.3-required test pressure, with the HRV removed/disconnected and the connection appropriately blinded, or use another engineered test isolation arrangement acceptable under B31.3 and to your inspector/AHJ.
After the hydrotest:
- Depressurize and drain the test water.
- Remove the test blind.
- Install the HRV.
- Verify the HRV set pressure/certification.
- Verify that the completed piping has the required hydrostatic relief protection.
- Verify that the HRV cannot be inadvertently isolated from the liquid-containing piping during normal operation.