Hydrostatic Testing
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Pneumatic Testing
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Test pressure is normally 30% higher than the design pressure
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Test pressure is normally 10% higher than the design pressure
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Recommended for high pressure applications
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Recommended only for low pressure applications
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Test media (Water) used is not compressible by pressure application
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Test media (Air) used is compressible by pressure application
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Energy stored per unit volume of water under test pressure is very negligible
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Energy stored per unit volume of compressed air under test pressure is very high
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Needs thorough cleaning after test to
eliminate moisture especially for service which are reactive to moisture / fluids
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Easy to clean after testing
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Pressure Relief devices are recommended to control sudden increase in pressure during testing
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Pressure relief devices are must during test to ensure no over pressurisation
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Chances of equipment/ Pipe / test apparatus
failures are very low
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Chances of equipment/ Pipe / test apparatus
failures are high
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Weight of equipment along with test medium as
water is high hence special attention should be given to floor and supporting arrangements
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Weight of equipment with test medium
as air is comparatively less
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Needs verification and examination of joints and connections before testing
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Needs very careful checking of weld joints thoroughly before testing
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Test media can be reused or transferred to other place after testing
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Test media can not be reused or transferred to other place after testing
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Skilled and semi skilled personnel can carry out the test
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Needs involvement of senior experienced staff to monitor the test.
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Recommended where large volumes are to be tested at same time (example pipe lines )
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If pipe lines are tested should be done with small segmental lengths at a time.
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Damages made by failures are less compared to failures in pneumatic testing
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Damages made by failures in testing are very huge and extensive
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Hydrotest is a regular day to day practice and safe procedure and it can be followed in any work site
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Needs special attention and safety precautions
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Pressure changes finite amount by infinitesimal change in volume
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Pressure change proportional to volume change
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