Hydrostatic tests are executed on pipes, valves, fittings, pressure vessels and other pressure equipment to ensure the absence of leakages before the delivery to a customer (End-User or EPC Contractor). Hydrostatic tests are executed either at the manufacturing plant or on-site at installation (both for brown and green-field installations) and are classified as NDT (non-destructive tests). In this article, we give an overview of this type of pressure tests.
HYDROSTATIC TEST MEANING
A hydrostatic test consists of filling the equipment with a fluid (generally colored water) until a set pressure is reached (example 1.5/2/3 times the nominal pressure, depending on the norms and local regulations) and keeping such pressure for a predefined time checking if leakages occur. To be significant, the test pressure shall always exceed the working pressure by a factor.
To check the absence of leakages, the staff in charge of the hydrostatic test executes visual inspections or uses specific tools that trace the absence of liquids leakages. The test is passed if the equipment is able to bear the test pressure for a prolonged time.
Before starting a hydrostatic test, the staff in charge should pay attention to the chemistry of the test fluid in terms of loads and corrosivity (e.g., chloride content of water), and how this may impact the equipment.
In case hydrostatic loads on a specific equipment are not possible or recommended, a pneumatic is an alternative option.
DIFFERENCE BETWEEN HYDROSTATIC AND PNEUMATIC TEST
As noted above, a hydrostatic test consists in filling a piece of equipment (as a vessel or a pipe spool) with a liquid, usually chlorinated water (to aid in visual leak detection) and apply a test pressure for a predetermined period of time. Therefore, the main feature of a hydrostatic test is that a liquid is used to test the equipment.
A pneumatic test uses pressurized air or an inert gas to test an equipment. Pneumatic tests are executed on low-pressure equipment or small parts due to the inherent danger of a compressed gas compared to pressurized liquids (as the water used for a hydro test).
A FAILED HYDROSTATIC TEST (VIDEO)
The video shows how a hydrostatic test is executed and a failure case: