[SOLVED] What Is Pneumatic Testing?

In circumstances when hydrostatic testing is not possible, for instance, the weight of hydro test water is too high for the pipe support system (e.g. Gas service piping) and when the introduction of water to the piping may be detrimental to the process (e.g. Catalyst or reactor contamination, cryogenic service system), then the components or system can be tested with nitrogen. Since the test medium is gaseous, it has the ability to compress and contain a large amount of stored energy (typically 200 times greater than a hydrostatic test at the same free volume and pressure condition) 😁 Extreme caution is required when using this technique 🙈 However, the specialized team at Intero Integrity Services will ensure design specifications are reviewed and a detailed risk analysis completed before testing with a compressible medium. [1]
Normally every EPC company has its own standard for the duration of tests. However, the recommended practice is that a QC inspector has to walk through the whole piping system and check for leaks. Every single length of piping, welds, bolted connections shall be visually examined for any leakage. The duration of this activity varies with the span of the piping system. For a larger piping system time taken for this activity is enough to clear the pressure test. In the case of a piping system having a smaller span, 1 hour time may be made as standard practice for hydrostatic testing. For the Pneumatic test, the test time is far lesser. [2]
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The test pressure shall be not less than 1.5 times the design pressure. When the design temperature is greater than the test temperature, the minimum pressure shall be calculated by eq. P T = 1,5P S T/S , where =allowable stress at test temperature, S=allowable stress at component design temperature, P=design gage pressure. The test pressure may be reduced to the maximum pressure that will not exceed the lower of the yield strength or 1.5 times the component ratings at test temperature. The pressure shall be continuously maintained for a minimum time of 10 minutes and may then be reduced to the design pressure and held for such time as may be necessary to conduct the examinations for leakage. Examinations for leakage shall be made of all joints and connections. [3]
Pneumatic testing is widely used to achieve minimum down time and economy and convenience of testing as compared to hydrostatic tests. It is also useful to detect very fine leak paths which may not be found in Hydrostatic testing.Pneumatic pressure testing of piping and vessels at moderate-to-high test pressures or at low test pressures with high volume is more hazardous than hydrostatic pressure testing because the stored energy is much greater with compressed gases. Air, however, (like all gases) is compressible and, as a result, much more energy has to be put into the gas to raise its pressure.In fact, at the pressure ranges normally used for testing water-piping systems 200 times more energy is stored in compressed gas compared to water at the same pressure and volume.So, should a joint, pipe, or any other component fail under test pressure when using compressed gas, the energy can be released with deadly force! (revised by Arnell Aldrich on October 29, 2021) [4]

Article References

  1. https://www.intero-integrity.com/services/pneumatic-testing
  2. https://whatispiping.com/hydrotest-vs-pneumatic-test/
  3. https://www.araner.com/blog/pressure-test-hydrostatic-pneumatic-requirements
  4. http://www.wermac.org/others/ndt_risks_pneu_testing.html
Kelly-Anne Kidston

Written by Kelly-Anne Kidston

I am a writer of many words, from fiction to poetry to reviews. I am an avid reader and a lover of good books. I am currently writing my first novel and would love to find some beta readers who are interested in getting an early look.

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