ASME B31.9 requires that utility piping be leak tested BEFORE initial operation. Hydrostatic testing shall be employed when possible. Pneumatic testing may be used instead of hydrostatic testing only under the limitations provided in para. 937.4.
All joints, including welds, shall be left uninsulated and exposed for examination during the test.
Piping designed for vapor or gas may be provided with temporary support if necessary to support the weight of the test liquid.
Expansion joints that cannot sustain the reactions due to test pressure shall be provided with temporary restraint or isolated from testing.
Equipment not to be subjected to the test pressure shall be isolated from the piping. If a valve is used to isolate the equipment, its closure shall be capable of sealing against the test pressure without damage to the valve. Flanged joints at which blinds are inserted to isolate equipment need not be tested.
Suppose the test pressure is to be maintained while the test fluid is subject to thermal expansion or any other source of overpressurizing during the test. In that case, precautions such as installing a relief device shall be taken to avoid excessive pressure.
Hydrostatic Testing
Water at ambient temperature shall be used as the test medium except where there is a risk of damage due to freezing. Another liquid may be used if it is safe for workmen and compatible with the piping.
Vents shall be provided at high points in the system to release trapped air while filling the system, and drains shall be provided at low points to completely remove the test liquid.
The system shall be examined to see that all equipment and parts that cannot withstand the test pressure are properly isolated. Test equipment shall be examined to ensure that it is tight and that low-pressure filling lines are disconnected.
A piping system shall be subjected to a hydrostatic test pressure that at every point in the system is not less than 1.5 times the design pressure.
The test pressure shall not exceed the maximum for any vessel, pump, valve, or other component in the system under test. A check shall be made to verify that the stress due to pressure at the bottom of vertical runs does not exceed either of the following:
(1) 90% of specified minimum yield strength
(2) 1.7 times the SE value in Mandatory Appendix I (for brittle materials)
Following the application of hydrostatic test pressure for at least 10 minutes, the piping and all joints and connections shall be examined for leakage. If leaks are found, they shall be eliminated by tightening, repair, or replacement, as appropriate, and the hydrostatic test shall be repeated until no leakage is found.
Pneumatic Testing
Compressed gas poses the risk of sudden release of stored energy. For that reason, pneumatic testing shall be used only within the following limitations:
(a) The piping system does not contain cast iron pipe or plastic pipe subject to brittle failure.
(b) The system does not contain soldered or solvent cement joints over NPS 2 (DN 50).
(c) The test pressure does not exceed 150 psig (1,034 kPa gage).
(d) The system will be used in gas service or, for other reasons, cannot be filled with water.
(e) Traces of a test liquid would be detrimental to the intended use of the piping.
Test Medium
The gas shall be nonflammable and nontoxic.
Preliminary Test
Prior to applying full pneumatic test pressure, a preliminary test of not more than 10 psig (69 kPa gage) shall be performed to reveal possible significant leaks. (This preliminary test may be used with hydrostatic or initial service testing.)
Pneumatic Test Pressure
(a) Except as limited in (b), the test pressure shall not exceed 1.25 times the design pressure. Pressure shall be applied in several stages, allowing time for the system to reach equilibrium at each stage.
(b) The test pressure shall not exceed the maximum allowable pneumatic test pressure for any vessel, pump, valve, or other component in the system under test.
After the preliminary test, the pressure shall be raised in stages of not more than 25% up to full pneumatic test pressure, allowing time to equalize strains and detect major leaks at each stage. After applying test pressure for at least 10 minutes, the pressure may be reduced to the design pressure, and an examination shall be performed for piping leakage.
Leaks may be detected by soap bubbles, halogen gas, scented gas, test gage monitoring, ultrasonic, or other suitable means. If leaks are found, the pressure shall be vented, appropriate repair or replacement shall be made, and the pneumatic test repeated until no leakage is found.
Initial Service Leak Test
For gases, steam, and condensate service at pressures not over 15 psig (103 kPa gage) and nontoxic, noncombustible, nonflammable liquids at pressures not over 100 psig (689 kPa gauge) and temperatures not over 200°F (93°C), it is permissible to conduct the system testing with the service fluid as outlined below.
A preliminary test with air at low pressure may be used. In any event, the piping system shall be brought up to operating pressure gradually with a visual examination at a pressure between one-half and two-thirds of the operating pressure. A final examination shall be made at operating pressure. If the piping system is free of leaks, it will have met the requirements of the code.