Hydro Testing- Vessels & Pipeline
A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas
cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves
filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in
visual leak detection, and pressurization of the vessel to the specified test pressure.
Pressure tightness can be tested by shutting off the supply valve and observing whether
there is a pressure loss. The location of a leak can be visually identified more easily if the
water contains a colorant. Strength is usually tested by measuring permanent
deformation of the container. Hydrostatic testing is the most common method employed
for testing pipes and pressure vessels. Using this test helps maintain safety standards
and durability of a vessel over time. Newly manufactured pieces are initially qualified
using the hydrostatic test. They are then revalidated at regular intervals according to the
relevant standard. In some cases where a hydrostatic test is not practicable a pneumatic
pressure test may be an acceptable alternative.[1] Testing of pressure vessels for
transport and storage of gases is very important because such containers can explode if
they fail under pressure
Hydraulic testing is a hazardous process and should be performed with caution by
competent personnel. Adhering to prescribed procedures defined in relevant technical
standards appropriate to the specific application and jurisdiction will usually reduce these
risks to an acceptable level.
A leak of high pressure liquid can cut or penetrate the skin and inject itself into body
tissues. This can cause serious direct injury to the operator, and if the fluid is toxic or
contaminated there will be additional adverse effects.
A pressurised hose that is not securely attached or which fails under pressure may
whip around spraying water or oil and could hit someone and cause injuries.
A whiplash arrestor can be used to restrain such hoses.
Enclosing the components to be tested, hazard signage, use of appropriate personal
protective equipment and providing barriers to access for non-essential personnel are
common precautions.
Equipment:
Pressure gauges
Water supply
Pumps and hoses for water filling
High pressure pump and hoses for pressurising
Means of measuring volumetric expansion when applicable
Vessel Pressure Testing
The Vessel Pressure Testing article provides you with information about pressure
vessel hydro-static testing requirements and related item in pressure vessel
inspection.
The requirements have been described based on ASME Code Section VIII. You
need to do this test after completion of the construction process, but before the
internal parts assembly and also before painting process.
This content covers all major requirements and provides you with guidelines for
test performance.
Please note that performing the pneumatic test instead of the Hydro-Static Test is
not allowed, and it can be replaced only when it is not possible due to the design
and process.
Vessel pressure testing requirements have been addressed in UG-99 and UG-100
in ASME Code Section VIII Div. 1.
These are important points, which you need to take care of in vessel pressure
testing:
Activities before vessel pressure testing, which
need to be checked by the manufacturer quality
control team and a third party inspector:
1. Checking all welding already finished and fully accepted by the NDT
examination per the project Inspection and test plan.
2. Making sure the inner part of the vessel is clean and free of remaining slag or
other elements.
making sure the external surface is dry for the correct execution of the visual
inspection during the vessel pressure testing.
3. Checking the pressure gauges' calibration tag and certificate and the range of
the lower limit and upper limit of the gauges. It needs to be between 1.5 and 4 of
the pressure test value.
4. Controlling testing equipment such as the test pump and housing for soundness
and tightness.
5. Making sure the test temperature will not violate the following values:
Min. Test temperature= MDMT + 30°F
Max. Test temperature = 120°F
MDMT is the pressure vessel minimum design metal temperature, and it is stated
in the pressure vessel design document.
This reduces the risk of a brittle fracture during the test.
6. Making sure which reinforcement pads are already soap tested.
7. Controlling the testing water quality and using corrosion inhibitor if it is
necessary or when the vessel metal is sensitive material
8. Checking of vents. It is required to be placed at high points of the vessel in a
position where it is possible to purge air pockets while the vessel is filling.
Activities during the pressure vessel hydro-static
testing that need to be checked by the
manufacturer quality control team and a third
party inspector:
1. Making sure the filling and pressurizing are done from the lowest point and
venting from the highest point.
2. Witnessing water overflow through the venting in order to assure that no air
bubbles remain in the vessel.
3. Controlling and witnessing which pressurizing is done in three stages as follow:
First Stage: Raise the pressure to 40% of the final pressure, stop pressurizing,
keep it for 5 minutes, and then make a fast visual inspection of the external
surface.
Second Stage: Restart pressurizing up to 70% of final pressure, stop the
operation, keep for 5 minutes and make a fast visual inspection on external
surface.
Third Stage: Restart pressurizing up to 100% of the final pressure, stop the
operation, and keep for 45 minutes.
4. When 45 minutes elapse, making sure the de-pressurizing is started and the
pressure is dropped to the “Inspection Pressure.”
This inspection pressure can be calculated as following:
Inspection Pressure = Hydrostatic Test Pressure / 1.3
Making sure a detail and a comprehensive inspection is carried out over the whole
body of the vessel and in the welding joints and attachments.
5. Making sure the pressure vessel hydro-static testing pressure calculated
correctly as following:
Hydrostatic Test Pressure = 1.3 x MAWP X Stress ratio
Stress Ratio = (Allowable Stress at Test Temperature)/(Allowable Stress at
Design Temperature)
6. Making sure the vessel is immediately and carefully drained after the test and
dried by air.
Activities after the pressure vessel hydro-static
testing that need to be checked by the
manufacturer quality control team and a third
party inspector
1. The pressure vessel hydro-static testing report needs to be prepared by the
manufacturer quality control team and signed by the third party or authorized
inspector.
2. If the test failed by leaking from weld joints or any other kind of defect, it is
necessary that the vessel is drained and dried and repaired based on approved
repair procedure. pressure vessel hydro-static testing needs to be repeated.
