Hydrostatic Testing Aircraft Pressure Vessels

February 2018

What is hydrostatic testing and why must it be done? Hydrostatic testing is a process to determine the strength and integrity of pressurized vessels. These include, but are not limited to; oxygen cylinders, fire bottles, emergency air bottles, reservoirs, and water bottles. These vessels hold content under pressure and often under extreme pressure. Over time the material that the vessel is made from can become deteriorated, weakening the strength and leaving it susceptible to catastrophic failure, resulting in damage to the aircraft and personnel.

The basic principle behind hydrostatic testing is a fairly simple one. The vessel is filled with water and placed in a “water jacket.” The vessel is then pressurized with water to the rated test pressure. The vessel will expand under this pressure and displace a small amount of water from the water jacket as it expands. The water volume expelled is measured and imputed to measure expansion. Once the pressure is released, the vessel will contract to nearly the same size as it started. The water that was previously expelled from the water jacket will be drawn back into the jacket. This measurement is also taken. It is these measurements that must meet CMM (Component Maintenance Manual) and CGA criteria to ensure the vessel is structurally sound. If during testing the vessel has a catastrophic failure, the result is not catastrophic at all. The water jacket merely expels the excess water, indicating a failure.

While the vessels may require hydrostatic testing per the Aircraft Chapter 5; the FARs (Federal Aviation Regulations) associated with hydrostatic testing do not fall under the jurisdiction of the FAA. The DOT (Department of Transportation) and Compressed Gas Association govern the requirements, test methods, and certification of qualified facilities. The facility performing these tests must be DOT certified and properly document the testing and test results.

Duncan Aviation is DOT certified for hydrostatic testing. If you have any questions, don’t hesitate to give me a call.