Hydrostatic test in steam boiler is one of non destructive examinations which should be performed for new steam boiler or steam boiler which has been repaired such as replace water wall, superheater, reheater, economizer and so on to. Hydrostatic test must be done to make sure that steam boiler is free from leakage before start up is performed. Before hydrostatic test is executed, inspection for all welds and installation of pressure parts should be done. Moreover inside and outside of steam boiler and pressure part shall be free from all dirt, scale, paint, debris, dirt, weld slag, rust, oil, spatter and all other foreign matter.
Before perform hydrostatic test (hydrotest) in steam boiler, the following matter should be prepared as follow:
- Non-destructive examination shall be verified to confirm acceptance as per Code and specification.
- Dimensional inspection.
- Full visual inspection for all welds.
- Boiler pressure part installation is completed.
- No painting work on pressure part before hydrostatic test.
- Inside and outside of boiler and pressure part shall be free from all dirt, debris, weld slag and spatter, oil, rust, scale, paint and all other foreign matter.
- Prepare and check valve line-up.
- All gags shall be installed on safety valve.
- Vent and drain are to be provided for the system before commence of hydrostatic test.
- All temporary fitting, blind flange shall be suitable for the test procedure and should not have defect that may cause failure during hydrostatic test.
- Fill boiler with treated water and free from mineral or other suspended matter (Demineralized water).
Requirement of gauge and record during hydrostatic test in steam boiler (hydro test):
- A minimum of 2 (two) pressure gauge shall be used for pressure tests. One shall be a pressure temperature recorder with a range suitable for recording of the test pressure. The full scale of the other pressure gauge shall preferably 1½ to 4 times of test pressure.
- The test pump and the line to be tested shall be provided with the separate indicating test gauges. In case of testing between a high and low point of the module, gauges shall be placed one at the top and one at the bottom to measure the pressured drop.
- The pressure gauge shall be calibrated and still valid before used. Any gauges showing incorrect zero error more than + 1% of full-scale range shall not be used without repair and recalibrate.
Hydrostatic test must follow the determined procedure which is generally as follows:
- Install suitable temporary fitting such as blind flange or end plate to close opening and ensure all of openings are closed except venting valve.
- Fill the steam boiler with treated water, free from mineral or other suspended matter at temperature not under 70 F or ambient temperature.
- Inspect leakage when steam boiler is being filled, remove air through venting valve, close it if there is not leakage and air is totally removed.
- Increase pressure gradually with maximum pressure rate 5 kg/cm2 until 1.5 times of maximum allowable working pressure for new boiler and 1.2 times for repaired boiler.
- Record pressure, time and temperature during test and inspect all of pressure parts of steam boiler at holding time of hydrostatic test approximately 10 minutes. 6. After hydrostatic test, the pressure should be release in a manner and at rate so as not to endanger personnel or damage equipment.