A hydrostatic test is procedure used to qualify newly manufactured cylinders, spheres and tubes used for the transportation of dangerous goods. Hydrostatic tests are conducted under the constraints of either the industry's or the customer's specifications, or may be required by law. The vessel is filled with a nearly incompressible liquid - usually water or oil - and examined for leaks or permanent changes in shape.  Testing of pressure vessels for transport and storage of gases is very important because such containers can explode if they fail under pressure. Red or fluorescent dyes may be added to the water to make leaks easier to see. The test pressure is always considerably higher than the operating pressure to give a margin for safety. This margin of safety is typically 166.66%, 143% or 150% of the designed pressure, depending on the regulations that apply. For example, if a cylinder was rated to DOT-2015 PSI (approximately 139 bar), it would be tested at around 3360 PSI (approximately 232 bar). Water is commonly used because it is nearly incompressible, therefore requiring relatively little work to develop a high pressure, and is therefore also only able to release a small amount of energy in case of a failure - only a small volume will escape under high pressure if the container fails. If high pressure gas were used, then the gas would expand to V=(nRT)/p with its compressed volume resulting in an explosion, with the attendant risk of damage or injury. This is the risk which the testing is intended to mitigate. Water is used mainly because it is cheap and easy.

The manufacturer’s markings on a pressure vessel include information regarding the date of manufacture, the manufacturers name or registered mark, the serial number of the unit and the specification or exemption to which the container complies. For pressure vessels that have been re-qualified one or more times, additional markings indicate the date(s) of any previous hydrostatic retests and identification markings of the retest facility.

Pressure vessels that have been hydrostatically tested and re-qualified must be marked by the retest facility with the facility retester identification number (RIN), and the retest date. Depending on the age of the container, it may contain none or many sets of retest markings. The oldest date marked on the container is the date of the original hydrostatic test carried out by the manufacturer, and is considered the manufacturing date. Any subsequent dates marked on the container are a record of the hydrostatic tests that the container has undergone.

Pipe line testing Hydrotesting of pipes, pipelines and vessels is performed to expose defective materials that have missed prior detection, ensure that any remaining defects are insignificant enough to allow operation at design pressures, expose possible leaks and serve as a final validation of the integrity of the constructed system.

to pressurize the vessel by filling it with water and to physically examine the outside for leaks. This type of test is suitable for containers such as boat fuel tanks, which are not pressure vessels but must work under the hydrostatic pressure of the contents. A hydrostatic test head is usually specified as a height above the tank top. The tank is pressurized by filling water to the specified height through a temporary standpipe if necessary. It may be necessary to seal vents and other outlets during the test.

Dimas Langga T

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