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According to ASME Section VIII Division I, hydrostatic pressure is conducted at the pressure of just one.5 times design pressure. If your vessel is design for holding 1.0 kg/cm2.g pressure, the hydrostatic pressure test needs to be done at 1.5 kg/cm2.g.
Hydrostatic test can also be applied to existing equipments and pipe lines to check for leakage after being repaired or maintained. Hydrostatic job number increases during plant Change period. Because in those days, the majority of equipments are opened for checking, inspection, clean-up, repairing, replacing song or performing internal modification.
The use of high pressure may be the main supply of hazards associated with hydrostatic pressure test. Hydrostatic test stores energy. High pressure could damage the facilities and endanger worker's safety. You ought to have included this into your own hazard identification.
Safety Checklist:
In order to prevent accident from hydrostatic test operation, we must make good preparation prior to perform the test, during the pressurization process and depressurizing operation. These jobs should be produced in the shape standard operating procedure. And listed here are the safety checklists for each stage.
Hydrostatic test preparation:
Specification sheet of the equipments as well as pipe line, which mentions pressure and temperature designs are available and complete.
- Hydrostatic test pressure and temperature standard are already clearly defined within the related document.
- Supported documents such as P&ID and isometric drawing can be found and comply with as built facilities at the field.
- Pressure test planning has to be distributed to all relevant sections in the plant site a minimum of two days prior to the execution date.
- Make good coordination among related sections which involve in the test.
- All test equipments and tools will be inspected for wear and damage.
- Pressure measurement tools are calibrated and their statuses of calibration are still valid.
- Pressure gauges used in the test have sufficient capacity. The gauges are suggested to have 150% of the maximum allowable working pressure.
- The pressure gauge is safety type, with blowout back.
- Pressure gauges should be installed in a proper location so that it can be simply read and don't create additional hazards to the hydrostatic test or expose personnels to the vessel being tested.
- All the temporary tools (for example valve, fitting, hoses, flanges, blind plate, etc) have to be rated a lot more than the utmost hydrostatic pressure.
- Isolate other equipments and pipe lines that don't include in the hydrostatic test.
- Vents can be found and installed our prime points to vent air. Check the vent line before testing and make sure it is not blocked.
- Choose drain valve at the lowest point in order to completely empty the vessel and pipe.
- Safety relief valve is already installed. Safety relief valve setting is 1.Five times maximum allowable working pressure.
- Safety relief valve is calibrated.
- Isolate the exam area and surround it keeping the vehicle safe line. Put appropriate safety sign at that area.
- Do not let individual who doesn't have any relation using the hydrostatic test, to enter the test area.
- If at all possible carry out the test from a remote area.
- Make sure that all pipe and vessel supports have been in good shape and have been inspected.
- All hoses should be tied down.
- Temperature of water should be a lot more than 16oC (60 F).
- The hydrostatic-pressurizing pump is finished keeping the vehicle safe relief valve.
- Wear proper personal protective equipments.
- Do not start the test if a problem is identified.
- Issue a work safety permit by authorized personnel.
Pressurization process:
- Remove all air in the vessel and pipe line by water through vent line.
- Pressurization is carried out gradually/slowly.
- Mark all leak points and repair them before preceding the exam.
- Do not monitor during pressurization step from the front of sight glass or level glass.
De-pressurization process:
- Start de-pressurization by opening gradually the vent valve. Get it done slowly.
- Don't open the drain valve if the vent valve if still closed. This is to prevent vacuum condition within the vessel.
- Open the cheapest drain point to completely remove water in the vessel and pipeline.
- Make sure that no remaining pressure trapped inside the pipe line or vessel.
