It is vital that new ammonia refrigeration systems, as well as new sections of the system or modifications of the system, undergo pressure testing, leak testing, and evacuation prior to startup to ensure the integrity of the closure welds, as part of the pre-startup safety review procedure. Before these tests can be conducted, pre-test preparations must be completed. First, we must verify that all equipment, components, and portions of the system involved in the pressure test has a pressure rating that meets the specified test pressure.
Note: Equipment and components that have been factory tested do not need to be part of the
pressure test but must be leak tested and evacuated prior to startup.
Additional Pre-Test Preparations: Ensuring that all joints remain uninsulated,
unpainted, and exposed until leak testing has been completed. We must also verify that these joints are free of rust, dirt, oil, and other foreign materials. Equipment and components that have been factory tested are isolated with valves, plugs, blank flanges or other suitable means to avoid or prevent damage from the test pressure. Atmospheric pressure relief devices are removed and the openings plugged or capped. Solenoid valves, pressure regulating valves, check valves, and other control devices are in the manually open position. Other valves, excluding those that lead to the atmosphere, are also in the open position, and valves that do lead to the atmosphere are capped, plugged, or locked in the closed position. The temperature of the piping system involved in the test will be above the ductile-brittle transition temperature, and examination of the piping to ensure that it is tightly connected.
Also, we must confirm that the means used to furnish the test pressure is equipped with
a pressure limiting device or a pressure reducing device, atmospheric pressure relief device, and pressure indicating gauge on the outlet side, and that the atmospheric pressure relief device has been set at a pressure higher than the specified test pressure, but low enough as to not allow deformation of any of the system components. It is also important to note that measures should be taken to protect personnel from the potential rupture of piping components during pneumatic testing of systems, and a preliminary test pressure of 25psig may be applied to identify any major leaks. As part of the pressure testing procedure requirements, the test gas must be introduced gradually into the system through a charging valve that is equipped with a shut-off valve, and a calibrated pressure gauge must be located on the portion of the system that is being tested to verify the test pressure.
Acceptable Testing Mediums: Nitrogen or compressed air may be used as the testing medium for the pressure and leak testing procedure.
Prohibited Testing Mediums: Oxygen, combustible gas or mixtures of combustible gases with a lower flammability limit of 13%, carbon dioxide, halocarbon refrigerants, and water or water solutions.
A preliminary test pressure of 25psig may be applied to identify any major leaks prior to
testing at the pneumatic test pressure. The pneumatic test pressure must be at least 110% of the design pressure and cannot exceed 130% of the design pressure.
Assuming that the design pressure of the high and low side of the system is 250psig, the pneumatic test pressure range would be 275psig to 325psig (e.g. 250psig x 1.10 = 275psig & 250 x 1.30 = 325psig). For large systems that are not completely visible to the testing operator, the test pressure can be gradually increased to one-half of the test pressure and then increased in steps of approximately one-tenth of the test pressure until the required test pressure has been reached. The test pressure must be held for a minimum of 10 minutes. After achieving successful pressure test results, the pressure may then be reduced to the leak test pressure.
The minimum leak test pressure will be the design pressure of 250psig, or a pressure
that is specified within a documented engineering design. The gas and bubble formation
test, or other methods of equal sensitivity, may be used for the examination of leaks. The examination of all joints and connections of the piping system must show no evidence of leaking. Any identified leaks must be repaired, defective material replaced, and the leak testing procedure must be repeated until the piping system is proven to be tight. Welds that have passed in-process examination, 100% radiographic examination and 100% ultrasonic examination are exempt from the pressure test and leak test requirements.
After achieving successful leak testing results, the system can then be purged of all
pressure and the atmospheric pressure relief devices that were removed for the test can be reinstalled in preparation of the evacuation procedure. The system must be evacuated to a pressure of 5,000 microns (0psig = 760,000 microns) unless compressed air was used as the test medium in which case it may then be evacuated to a pressure of 1,000 microns before the reintroduction of the refrigerant.
Records of the testing shall be retained for 3 years and must include the procedure specification, procedure qualification, performance qualification records, and the results of weld examinations other than visual, records for testing of the piping systems including the date of testing, the identification of the piping systems tested, the testing medium used, the test pressure utilized, and the signature of the examiner and inspector.
Sources: ANSI/IIAR 5 - 2019 (5.5) & ASME B31.5 - 2022 (538 / 539)
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