Among the tests mentioned above, the hydro test is one of the most common NDT for pipes and fittings.
Hydrostatic testing / Hydro testing is executed on piping (pipes, valves, fittings) and / or vessels to ensure the equipment is not subject to leakes when filled with a pressurized liquid. Tests are executed either in the manufacturing plant or on-site when the equipment is obviously out of service. Hydro tests can be execute both on newly manufactured equipment and material already in operation on the field (in this case, a deep cleaning is necessary before performing the test) or repaired equipment.
How does the hydrostatic test work? The test consists in filling the equipment to be tested with a fluid (generally colored water) as long as a set pressure within the equipment is reached. To be significant, the applied pressure shall exceed the working pressure of the product by 150% or more (depending on specific regulations or buyer's requirements). Once applied, the target pressure has to be withstand by the equipment for a specific duration. During this time, the testing staff checks whether the equipment leaks in some points or not. The visual inspection can be integratrated by using tracers and dyes that facilitate the detection of leakages.
Before starting an hydrostatic test, engineers should consider the gravity and the chemistry of the hydro test fluid both in terms of loads and corrosivity (e.g., chloride content of water), and how this may impact the equipment.
When hydrostatic loads on a specific piece of equipment are not acceptable, a possible alternative is the pneumatic test or other gas leakeage testing methods.
Example of a failed hydro test on pipeline equipment: