If you&#;re in an industrial or manufacturing setting, you may have heard of the two types of tests used to assess the quality and safety of equipment &#; pneumatics tests and hydrostatic tests. Both are designed to evaluate the structural integrity of machines, pipes, and other objects, but there are key differences between the two that can make one more suitable for certain situations than the other. In this blog post, we&#;re going to look at the differences between these two types of tests and discuss when you should use a pneumatic or hydrostatic test.
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Pneumatic tests are designed to assess the strength and pressure capacity of a product. During a pneumatic test, compressed gas or air is used to expand and pressurize the object being tested. As the pressure is increased, the object is monitored to determine whether or not it can withstand a certain level of pressure. During the test, engineers measure the results and compare them to a predetermined standard.
Similarly, a hydrostatic test assesses the structural integrity of a vessel or container, such as a tank, pipe, gas cylinders, or boilers. During a hydro test, the object is filled with a pipe testing medium, such as water, and pressure that meets the hydrostatic test requirements is then applied to the object. The pressure is gradually increased and decreased to check for leaks or weak points in the object. If a leak is detected, it indicates that there is a weak point in the vessel or container, and it must be repaired or replaced before it can be used.
Determining whether you need to use pneumatic pressure testing or hydrostatic pressure testing for an industrial application can be a complex decision. Both tests offer critical advantages and it is important to consider your specific application and study each option carefully to select the most suitable one. Pneumatic pressure testing is often more suitable for complex systems or components, whereas hydrostatic pressure testing is typically the best choice for inspecting pipelines and tanks.
When selecting which form of pressure testing to use for an industrial application, factors such as cost, time constraints, and exact accuracy of results should be heavily weighed in. Considering these factors and comparing them with the advantages and disadvantages of each pressure testing method can help you make an informed decision as to which method to use. Ultimately, it is important to ensure the system is tested to the specified level of accuracy and safety to maintain reliability of operation.
Pneumatic pressure testing is generally more economical than hydrostatic testing, is less time consuming, and produces accurate results. It is often used in hydraulic systems and other systems with moving parts, and is a popular choice if the components of the system are already air- or gas-rated and designed to hold the applied pressure without bursting. However, these tests can only serve as an indication of pressure and do not provide absolute proof of leakage or integrity.
On the other hand, hydrostatic pressure testing is used to simulate the effects of liquid under actual operating conditions. The advantage of hydrostatic pressure testing is that it provides absolute proof of the validity of the system and allows for complete inspection of the entire system for leaks. Because it is the only form of pressure testing that can detect and correctly measure a tiny leakage, it is often used for critical industrial applications.
If you&#;re looking for dependable, accurate hydrostatic and pneumatic testing services, then get in touch with Hydrotech. Our experienced team of professionals can ensure that all of your hydrostatic testing needs are met &#; and at a reasonable rate. Contact us today to find out how we can provide hydrostatic testing services for your business.
A hydrostatic test or hydro test is a widely used method to ensure leak tightness and safety of pressure vessels, piping systems, pipeline systems, plumbing systems, tanks, boilers, cylinders, and other system components. The test is performed by subjecting the material to a predecided controlled pressure known as test pressure and then checking the material response under pressure. It is a type of pressure testing performed before commissioning. In this article, we will learn about the hydrostatic testing procedure of piping systems in detail.
A pressure test of pipes is always required for a new pressure piping system before use or an existing pressurized system after repair or alteration to ensure the following:
Subsequent to repairs and heat treatment and prior to the initial operation or commissioning of any plant it has to be ensured that there is no evidence of leakage by Pressure Testing. As the main aim of performing pressure testing in piping systems is to ensure leak tightness, it is also known as the leak test of piping.
As per the governing code, a pressure test has to be performed on the piping system after all hot works have been completed on a certain piping system. Here the term hot work means everything related to welding or post-weld heat treatment (PWHT). PWHT also has the potential of degrading the mechanical properties of piping, in case not addressed properly. And this is the reason why the code calls for NDT after the PWHT operation.
In case after carrying out pressure testing, some modification has to be made requiring hot work, which calls for a retest as per code. Here code specifies that the minor repairs/modifications may be waived off provided adequate measures have been taken to ensure sound construction. Now this decision as to which repairs or modifications may be waived off should be taken very carefully. Normally, the maximum extent of repairs not requiring retesting shall be the tack welding of any piping support or pad. Anything else shall be done following a retest.
Pressure testing and conducting 100% radiography or ultrasonic inspection shall not be interchanged. In case carrying out of hydrostatic or pneumatic test stands impractical then 100% radiography or ultrasonic testing may be performed but in addition to this, it is advisable to check that the whole piping and its components have been supplied against acceptable ASTM standards and required test certificates are available.
Conducting 100% radiography of all the weld joints assure that your weld joints are defect-free but can never provide you with the assurance of mechanical integrity of a system.
This is also to be noted that radiography / ultrasonic inspection shall also not be waived off if the pipeline is to be hydrostatically tested. This may pose an additional safety risk during the test. Moreover, some defects in the weld zones may prove to be detrimental way after being taken in service due to severe extended service conditions.
In the process piping industry, two methods are widely used for pressure testing of piping or equipment. They are
Pressure tests (both hydrostatic and pneumatic) must always be performed under controlled conditions, following an approved test plan, and documented in a test record. A single approved test plan could be used for several similar tests, but for each test, a separate test record is required.
Normally the following basis is followed in the process piping industry for the selection of hydro or pneumatic tests in piping.
Hydro test or Hydrostatic test is a type of pressure test performed on piping, pressure vessels, and other pressurized systems to check system integrity under pressure conditions. A hydrostatic test is performed by using water as the test medium.
ASME Code B 31.3 provides the basis for test pressure. The minimum hydrostatic test pressure for metallic piping shall be as per the following equation:
Here,
Pt=the minimum test gauge pressure
Pd=internal design gauge pressure
St=allowable stress value at the test temperature
Sd=allowable stress value at design temperature.
The maximum allowable value of St/Sd is 6.5
Note that, ASME B31.3 provides a provision to reduce the hydrostatic test pressure in piping under certain conditions. Quoting the Process Piping code ASME B31.3 the rules for reduced test pressure are:
&#;If the test pressure would produce a circumferential or longitudinal stress (based
However, the hydrostatic test pressure must not be less than the design pressure.&#;
on minimum pipe wall thickness) in excess of yield strength at test temperature or is greater than 1.5 times the component rating at test temperature, the test pressure may be reduced to the maximum pressure that will not exceed the lesser of the yield strength or 1.5 times a component rating at test temperature.
Normally every EPC company has its own standard for the duration of tests. However, the recommended practice is that a QC inspector has to walk through the whole piping system and check for leaks. Every single length of piping, welds, and bolted connections shall be visually examined for any leakage. The duration of this activity varies with the span of the piping system. For a larger piping system time taken for this activity is enough to clear the pressure test. In the case of a piping system having a smaller span, 1 hour time may be made as standard practice for hydrostatic testing. For the Pneumatic test, the test time is far less.
As per ASME B31.3, The leak test pressure has to be maintained for at least 10 min and then all joints and connections shall be examined for leaks.
The following are the basic steps involved in the hydrostatic testing of piping systems:
As the name signifies, the test has to be performed using clean potable water free from suspended solids. However different codes specify different requirements for water quality. Hence, hydro tests need to be performed following those instructions.
The piping network and the connected equipment must be prepared thoroughly before proceeding with pressure tests like hydro or pneumatic testing. Codes like ASME B31.3/ ASME B 31.1 and local company instructions normally provide guidelines for such preparation.
Piping systems that are normally open to the atmosphere, such as drains, vents, discharge piping from pressure-relieving devices, sewers, and stack downstream of the seal drum, need not be subjected to the piping test pressure.
For some countries, The provincial local inspector shall be notified at least 48 hours in advance of pressure testing of piping under the jurisdiction of the provincial safety code for witnessing at his/her option.
Underground portions of piping systems may be tested and covered before testing aboveground portions.
Roughly, The following steps should be followed for preparing the piping system for leakage testing.
The first step is to compare the piping isometrics with the P&ID drawings to check if any discrepancy exists. All valve types, flow directions, branch tie-ins, and any material changes, etc are reviewed thoroughly. In-line components are verified and ensured that they are able to withstand the test pressure.
All sorts of ultrasonic and radiographic inspections or checks must be carried out before the actual pressure test is started. Conducting 100% radiography of all the weld joints assures that your weld joints are defect-free but can never provide you with the assurance of the mechanical integrity of a system. This is also to be noted that radiography / ultrasonic inspection shall also not be waived off if the pipeline is to be hydrostatically tested.
All joints, welds (including structural attachment welds to pressure-containing components), and bonds shall be left uninsulated and exposed for examination during leak testing as per Section 345.3.1 of ASME B31.3, except that joints previously tested in accordance with this Code may be insulated or covered.
If required Pipings designed for vapor or gas services shall be provided with additional temporary supports, to support the weight of the test liquid as the test liquid is heavier than the service fluid.
All Spring supports shall be kept in locked condition during hydrostatic testing. Holding pins shall not be removed from spring supports until testing is completed and the system is drained. Care shall be taken to avoid overloading any parts of the supporting structures during hydrostatic testing.
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If there is an expansion joint in the piping system under the leakage test, the following criteria shall be applied.
Equipment that is not to be tested must be either disconnected from the piping or isolated by blinds or other means during the test. A valve may be used provided the valve is suitable for the test pressure.
Rotary machinery, such as pumps, compressors, or steam turbines, have lube and seal oil systems that could be impaired by the presence of water. These systems shall not be subjected to the piping test pressure.
Clean water that will not corrode and/or damage the test system shall be used for hydrostatic tests. If municipal water is not available, supply water may be obtained from a native water supply. Water containing silt or suspended material shall not be used, and a suitable filter with 40 mesh should be provided in the filling line. A mixture of glycol-water shall be used where the ambient temperature may reach less than 0°C (32°F) during testing or prior to dry-out
If Temporary spades and blanks are installed for testing purposes, those must be designed to withstand the test pressure without distortion. The presence of spades shall be clearly visible during testing. The recommended practice is to use standard blind flanges as per ASME B16.5 or B16.47 and spades acc. to ASME B16.48.
Check Valves shall have the piston or flap removed for testing, where pressure can not be located on the upstream side of the valve. The locking device of the flap pivot pin shall be reinstated together with the flap and a new cover gasket shall be installed after the completion of the test.
Wherever applicable All hot works, related to welding or the post-weld heat treatment have to be completed before the Hydrostatic test.
It is necessary to install safety barriers around the piping system under test prior to starting pressurization related to testing. Public Address announcements and access restriction procedures such as permits to work shall be implemented. Under no circumstances should anyone other than an authorized person be allowed within the safety barriers.
Prior to the leakage test, Control Valves and soft-seal block Valves shall be removed from the piping and replaced with pipe spools. However, All welded Valves need to be tested along with pipings otherwise Radiographic Testing of golden joints (welded) will be required.
Prior to the pressure test following should be checked :
The individual system documentation i.e. test pack shall be available prior to any testing and shall include information such as test limits, test pressure, test medium, duration, test blinds, blind flanges, vents, and drains.
The use of marked-up P&IDs coupled with isolation registers should be utilized to identify the locations of blinds, Valves, vents, and drains.
Records shall be made of each piping system test. In general, these records shall include the following information:
Forms, when completed, shall be retained in the Construction Contractor&#;s QC file as a permanent record.
Testing equipment such as pumps, manifolds, pressure, and temperature recorders, and pressure gauges should be within calibration/certification (as per company procedures) and connected to the lowest convenient connection within the system to ensure the best results.
Even though proper industry-approved methods are followed for pressure testing, still due to some negligence hazards do happen. Some of the most common reasons for failures during hydro tests and pneumatic tests are:
So it is always a good idea to follow safe work practices for Hydro testing. The below-mentioned steps can be followed to avoid hazards of Pressure Testing:
The following section provides a sample of the hydro test checklist to inform the major points that must be considered.
Hydrotesting Checklist Pre HydroTest Checklist Sr NoDescriptionCompliedNot CompliedRemarks1All Affected people like the Owner, Managers, Workers, and Suppliers, informed 2Test pressure and duration received or estimated 3Standard Operating Procedure identified 4The Pre-test safety plan completed 5Required workers properly trained 6Test Equipment inspected, calibrated, and certified 7Test Temperature verified 8Test area barricaded and warning signs posted to keep non-essential members outside the hydro-test zone 9A walk-down inspection performed 10Hydrotest system preparation proper 11Vent Valve, Block Valve closed 12All joints are exposed, No insulation 13System parts are properly aligned 14Torque on bolted connections as per manufacturer guidelines 15Lockout tag-out finished as per guidelines 16Emergency contact information collected 17proper isolation from equipment and non-test parts following SOP performed 18A pressure relief valve installed Checklist during Hydrotest 19Hydro test equipment properly installed 20Working professionally with all PPE equipment 21Pressure is applied gradually following work procedure/standards 22Pressure maintained for the pre-decided time duration 23All exposed joints are thoroughly checked for leakage potential. Post-Hydrotest Checklist 24Repairs started after the release of Hydrotest Pressure. 25Pressure is released gradually. 26Water was disposed of as per the procedure 27Repairs performed following procedures Table 1: Hydrotest ChecklistThe cost for hydrostatic testing of piping systems can vary widely depending on a variety of factors, such as the size and complexity of the system, the type of test fluid used, and the location of the system. Other factors that can affect the cost include the need for special equipment, such as pumps and gauges, and the cost of any necessary repairs or maintenance.
In general, the cost of hydrostatic testing can range from a few hundred dollars to several thousand dollars or more. For small, simple systems, the cost may be relatively low, while larger, more complex systems can require more time, labor, and equipment, resulting in higher costs.
To get an accurate estimate of the cost of hydrostatic testing of a specific piping system, it is best to contact a qualified testing contractor or service provider and request a quote based on the specific details of the system in question.
Hydrotest and hydrostatic tests are often used interchangeably to refer to the same testing process, which involves filling a piping system or component with a fluid, usually water, and subjecting it to pressure to check for leaks or weaknesses.
The pneumatic test is a type of pressure test for checking system integrity under pressurized conditions and is applied to systems where the hydrostatic test is difficult to apply. A pneumatic test uses clean, dry, and oil-free air, nitrogen, or any non-flammable and non-toxic gas.
The pneumatic test pressure shall be as per the following equation:
Pneumatic test for piping is done in three steps: Pressurization, Inspection, and De-pressurization.
To avoid brittle fracture, the pressure shall be increased by less than 10% of test pressure per minute
into the system allowing adequate time for temperature equalization. The pressurization shall follow this sequence:
The depressurization rate shall be calculated, considering the Joule-Thomson effect, to prevent brittle fracture while the system remains under stress.
Inspection shall only be permitted after the pneumatic test pressure has been achieved, held, and
then reduced to the design pressure
Pneumatic tests are potentially more dangerous than hydrostatic tests because of the higher level of potential energy stored during compressing of the gas. Care must be exercised to minimize the chance of brittle failure during testing by initially assuring the system is suitable for pneumatic testing.
Pneumatic tests could be performed only when at least one of the following conditions exists:
Using a pneumatic test instead of hydrostatic requires approval from proper authority or body.
The following table lists the major differences between hydrostatic and pneumatic testing.Hydrostatic TestingPneumatic TestingHydrostatic test pressure is normally 50% higher (As per ASME B31.3) than the design pressure.Pneumatic test pressure is normally 10% higher than the design pressureHydrotest is recommended for high-pressure applications.A Pneumatic test is recommended only for low-pressure applications.In a hydro test, the test media (Water) used is not compressible by pressure application.In a pneumatic test, the test media, Air is compressible by pressure application.In hydrostatic testing, the energy stored per unit volume of water under test pressure is negligible.The energy stored per unit volume of compressed air under test pressure in the case of a pneumatic test is very high.Needs thorough cleaning after the hydrostatic test to eliminate moisture, especially for services that are reactive to moisture/fluids.Easy to clean after pneumatic testing.Pressure Relief devices are usually recommended to control a sudden increase in pressure during hydro testing.Pressure relief devices are a must during the pneumatic test to ensure no over-pressurization.Chances of equipment/ Pipe/test apparatus failures are very low during hydro testing.Chances of equipment/ Pipe/test apparatus failures are high during pneumatic testing.The weight of equipment along with the hydro test medium as water is high hence special attention should be given to the floor and supporting arrangements.The weight of equipment with the pneumatic test medium as air is comparatively less.Needs verification and examination of joints and connections before testing.Needs very careful checking of weld joints thoroughly before testing.In hydrostatic testing, the test media can be reused or transferred to other places after testing.In pneumatic testing, the test media can not be reused or transferred to other places after testing.Skilled and semi-skilled personnel can carry out the test.Needs the involvement of senior experienced staff to monitor the test.Recommended that large volumes are to be tested at the same time (for example pipelines).If pipelines are tested should be done with small segmental lengths at a time.Damages made by failures are less compared to failures in pneumatic testing.Damages made by failures in testing are very huge and extensive as compared to hydrostatic testing.Hydrotest is a regular day-to-day practice and safe procedure and it can be followed in any work site.Needs special attention and safety precautions for performing a pneumatic test.Pressure changes finite amounts by an infinitesimal change in volume.The pressure change is proportional to the volume change.Table 2: Hydro Test vs Pneumatic Test
Both hydro test and hydrostatic test refer to the same pressure test method. Hence, both are the same and there is no difference between the Hydrotest and Hydrostatic test.
The hydrostatic test pressure considered for pipeline systems is 1.25 times the design pressure.
A Hydrostatic test is done by filling the system with water and then pressurizing it to hydro test pressure (usually 1.5 times of design pressure). The pressurized system is kept for a pre-decided time and then visually all joints are checked for any leakage.
Yes, a hydrostatic test can cause damage. Some examples of hydro test hazards are provided here.
Hydrostatic testing is the safest type of pressure testing as it generates considerably less stored energy which in turn involves less risk to workers.
Most of the codes and standards prefer to use hydro testing as the best method for pressure integrity checks. However, in some situations, the hydrostatic test may be avoided. An example is a golded joint.
A golden joint is usually the final joint to weld the new pipe with the existing pipe. As the Hydrostatic test is usually not feasible, NDE (ultrasonic or radiographic test) is performed in place of pressure testing.
It depends on various factors like the governing codes, standards, and local procedures; the length of the system, the number of joints to check, etc. Usually, the system should be pressurized for a least 10 minutes.
The pipes that are open to the atmosphere, such as vents or drains downstream of the last shutoff valve, Non-hazardous lines open to the atmosphere, lines connected to silencers, open-ended portions lines, and open funnels do not require pressure testing.
The following video tutorial explains the major differences between the Hydrostatic test and the Pneumatic test.
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