Why are pressure vessels tested with liquids instead of air?

Hydrostatic testing is the most common and preferred method for testing pressure vessels, pipelines, and boilers for strength and leaks. It usually involves filling the container with water and pressurizing it to a specified test level. Water is chosen over gases because it is much safer; if a fracture occurs during testing, water releases far less explosive energy since it does not greatly increase its volume upon rapid depressurization.

What we know

• Hydrostatic testing is preferred over pneumatic testing because it is safer, releasing much less energy if a fracture occurs. [2]
• A hydrostatic test involves filling the vessel with a liquid, usually water, and pressurizing it to test for strength and leaks. [3]
• Strength during a hydrostatic test is usually evaluated by measuring the permanent deformation of the container. [3]
• Pneumatic tests use air or another gas, which can expand explosively during rapid depressurization if a failure happens. [2]

Where to go next

• compared withWhat is a pneumatic pressure test?
• how it workedHow do ultrasonic testing and radiography check vessels?
• the bigger pictureWhat are pressure vessels used for?
• how we knowWhat does the ASME Boiler and Pressure Vessel Code regulate?
• what followedHow do pressure relief devices protect systems?
• an unexpected connectionHow does blood pressure compare to industrial pressure vessels?Both concepts deal with containing liquids or blood inside flexible or rigid walls under pressure, yet one is measured in millimeters of mercury for medical diagnostics while the other undergoes destructive industrial testing.

Sources

• [1]pressure vessel (Wikidata Q740460) · CC0 1.0
• [2]Pressure vessel · CC BY-SA 4.0
• [3]Hydrostatic test · CC BY-SA 4.0
• [4]Pressure · CC BY-SA 4.0
• [5]Blood pressure · CC BY-SA 4.0