Hydrostatic Test or hydro test is not required for pipe fittings unless specifically requested by the purchaser. Code mandate that fittings shall be able to withstand under pressure required by applicable Piping Code. A hydrostatic test is a pressure test in which the pipe or other component is pressurized to evaluate its integrity. This test is used to evaluate the structural integrity of pipeline or other pressure containing infrastructure. During the test, the pipe is filled with water and the water pressure is increased, held for certain duration, and then released. The test is performed at pressures above the normal operating conditions of the pipeline. Normally the test is performed when the pipeline is put into service, but can also be conducted to evaluate the integrity of the infrastructure after a certain length of operation. It is important to remove all water used for hydrostatic test and dry the pipeline before operation; otherwise the locations where water accumulates become susceptible to internal corrosion. To avoid this issue, sometimes nitrogen is used for pressure testing. When this type of test is not possible or recommended, the pneumatic test is a suitable alternative.
A pneumatic test uses compressed air or inert gases to test a piece of equipment. Pneumatic tests are generally executed on low-pressure equipment or small parts or when a hydro test cannot be executed for whatever reason.
Burst Test or Proof Test
To qualified the design of the pipe fitting, manufacturer performed a various test including burst test to ensure that design will meet the all the standard & code requirements. In this test, a pipe & fittings are welded and a dummy pipe spool is prepared. This pipe spool is then pressurized to pre-define calculated burst test pressure. And in some case, they keep pressurizing the fitting till it actually burst. But it is very dangerous so nowadays they use finite element method or similar computerize program to establish design. If the fittings withstand the test, the entire future product manufactured using that design will consider safe to use.