Pressure tests are a non-destructive way to guarantee the integrity of equipment such as pressure vessels, pipelines, plumbing lines, gas cylinders, boilers and fuel tanks. It is required by the piping codes to confirm that a piping system is able to bear its rated pressure and it has no leaks. Pressure testing, also called hydrostatic testing, is carried out after the cooling or heating installation of any pipeline and before it is put into use.
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By performing a pressure test we find a reliable method for testing all types of pipework, including the ones in district cooling or district heating systems. This type of analysis, besides guaranteeing the right functioning, will also allow us to detect if there are leaks in a specific pipe so that reparations can be made.
The most widely used code for pressure and leak test is the ASME B31 Pressure Piping Code. Among its several sections, the requirements and procedures listed in the codes below are followed by Araner:
- ASME B31.1 Power Piping
- ASME B31.3 Process Piping
- ASME B31.5 Refrigeration Piping
Pressure tests may be done either with liquid, usually water (hydrostatic), or with gas, usually dry nitrogen (pneumatic).
General requirements of pressure test
- Stress exceeding yield strength: the test pressure may be reduced to the maximum pressure that will not exceed the yield strength at test temperature.
- Test fluid expansion: If the test pressure is to be maintained for a period of time and the fluid in the system is subject to thermal expansion, precautions shall be taken to avoid excessive pressure.
- Preliminary pneumatic test: a preliminary test using air at no more than 170 kPa (25 psi) gage pressure may be made prior to hydrostatic or pneumatic testing to locate major leaks.
- Examination for leaks: a leak test shall be maintained for at least 10 minutes, and all joints and connections shall be examined for leaks.
- Heat treatment: Leak tests shall be conducted after any heat treatment has been completed.
- Low-test temperature: The possibility of brittle fracture shall be considered when conducting leak tests at metal temperatures near the ductile-brittle transition temperature.
- Personnel protection: Suitable precautions in the event of piping system rupture shall be taken to eliminate hazards to personnel in the proximity of lines being tested.
- Repairs or additions after leak testing: If repairs or additions are made after the leak test, the affected piping shall be retested.
- Test records: Records shall be made of each piping system during the testing, including:
- Date of test
- Identification of piping system tested
- Test fluid
- Test pressure
- Certification of results by examiner
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Preparation for testing
- Exposure of joints: all joints including welds not previously pressure tested shall be left uninsulated and exposed for examination during the test.
- Addition of temporary supports: piping systems designed for vapor or gas shall be provided with additional temporary supports if necessary to support the weight of the test liquid.
- Restraint or isolation of expansion joints: expansion joints shall be provided with temporary restraint if required for the additional pressure load under test.
Isolation of equipment and piping not subjected to pressure test: Equipment that is not to be subjected to the pressure test shall be either disconnected from the system or isolated by a blank or similar means.
Figure 1: Isolation of piping
Hydrostatic Test
- Test fluid: The fluid shall be water unless there is the possibility of damage due to freezing or to adverse effects of water on the piping or the process. In that case, another non-toxic liquid may be used.
- Provision of air vents at high points: Vents shall be provided at high points of the piping system to purge air pockets while system is filling.
- Pressure and procedure: The pressure limits are different for ASME B31.1 and ASME B31.3.
ASME B31.1 Test Power Piping
The hydrostatic test pressure at any point in the piping system shall not be less than 1.5 times the design pressure, but shall not exceed the maximum allowable test pressure of any non-isolated component, nor shall it exceed the limits of calculated stresses due to occasional loads.
ASME B31.3 Test Process Piping
The test pressure shall be not less than 1.5 times the design pressure. When the design temperature is greater than the test temperature, the minimum pressure shall be calculated by eq. P T = 1,5P S T/S , where =allowable stress at test temperature, S=allowable stress at component design temperature, P=design gage pressure. The test pressure may be reduced to the maximum pressure that will not exceed the lower of the yield strength or 1.5 times the component ratings at test temperature. The pressure shall be continuously maintained for a minimum time of 10 minutes and may then be reduced to the design pressure and held for such time as may be necessary to conduct the examinations for leakage. Examinations for leakage shall be made of all joints and connections.
Pneumatic Test
- Precautions: Pneumatic testing involves the hazard of released energy stored in compressed gas. Particular care must be taken. It is recommended to be used only when piping systems are so designed that they cannot be filled with water, i.e, refrigerant systems; or when piping systems are to be used in services where traces of the testing medium cannot be tolerated.
- Test fluid: The gas used as test fluid, if not air, shall be nonflammable and nontoxic, such as nitrogen.
- Pressure and procedure: the pressure limits and methodology is different for the codes mentioned above.
ASME B3.1 Test Power Piping
The pneumatic test pressure shall not be less than 1.2 nor more than 1.5 times the design pressure of the piping system. It shall not exceed the maximum allowable test pressure of any non-isolated component. The pressure in the system shall gradually be increased to not more than 1/2 of the test pressure, after which the pressure shall be increased in steps of approximately 1/10 of the test pressure until the required test pressure is reached. The pressure shall be continuously maintained for a minimum time of 10 min. It shall then be reduced to the lower of design pressure or 100 psig [700 kPa (gage)] and held for such time as may be necessary to conduct the examination for leakage. Examination for leakage by soap bubble or equivalent method shall be made of all joints and connections.
ASME B31.3 Test Process Piping
The test pressure shall not be less than 1.1 times the design pressure and shall not exceed the lower of 1.33 times the design pressure or the pressure that would produce a nominal pressure stress or longitudinal stress in excess of 90 % of the yield stress of any component at the test temperature. The pressure shall be increased until a gage pressure, which is the lower of 0.5 times the test pressure or 170 kPa (25 psi), at which time a preliminary check shall be made. Thereafter, the pressure shall be gradually increased in steps until the pressure is reached, holding the pressure at each step until the piping strains are equalized. The pressure shall then be reduced to the design pressure before examining for leakage. During the test, a pressure relief device shall be provided, having a set pressure not higher than the test pressure plus the lower of 345 kPa (50 psi) or 10% of the test pressure.
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ASME B31.5 Test Refrigeration Piping
The test pressure shall be at least 1.1 and shall not exceed 1.3 times the design pressure of any component in the system. The pressure in the system shall be gradually increased to 0.5 times the test pressure, after which the pressure shall be increased in steps of approximately 1/10 of the test pressure until the required test pressure is reached. The test pressure shall be maintained for at least 10 minutes. It may then be reduced to the design pressure and conduct the examination for leakage. During the test, a pressure relief device shall be provided, having a set pressure above the test pressure, but low enough to prevent permanent deformation of any of the system components.
What are the benefits with outsourcing pressure testing?
Working with a company that specializes in heating and cooling services, maintenance and testing is often more beneficial than integrating dedicated personnel inhouse, reducing cost, time, and resources.
Other benefits of outsourcing a pressure test include:
- Faster turnaround time
- Increased safety for your staff
- mproved product quality assurance
- Decreasing repair costs
- Minimizing risk exposure and liability claims.
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Why is it important to do a pressure test with asme procedure?
Pressure tests carried out according to the asme procedure allow us to guarantee the correct performance of the system and to detect that there are no leaks and that the installation is robust.
That is why it is important to consider specialised district energy contractors such as Araner. It is essential to work with top-notch, quality-oriented professionals to ensure the safety of the plant.
ARANER, the industrial cooling engineering experts
We are experts in designing, manufacturing and installing tailor-made industrial cooling solutions with a positive economic impact. We have worked worldwide in the development of Turbine Inlet Air Cooling, District Cooling and Thermal Energy Storage. Get in touch with our experts if you are interested in any of our solutions or if you need technical advice. We will be glad to help!
What Is Pneumatic Testing and Why Is It Required
Ensuring that all equipment is functional and ready to go can save you the hassle in the long run -- plus lots of money and stress. Your pressure systems are no exception. For your piping systems, you will need to rely on a pressure test to test its functionality.
Pneumatic testing is a key pressure test that can help you assess your systems. Continue reading to learn what pneumatic testing is and why it may need to be performed on your pressure systems.
The Basics of Pneumatic Testing
At the core of pneumatic testing is the use of air -- or another inert gas medium like nitrogen or helium -- to pressurize a piping system. The air or nitrogen is confined throughout the piping system to mimic a high-pressure environment at 100% of the system&#;s design.
Air and nitrogen are the most commonly used mediums since they are affordable. Helium is more expensive but can be used as the most accurate tracer gas if deemed necessary.
Why Pneumatic Tests Are Necessary
Pneumatic tests and all pressure tests are necessary to ensure your pressure system's safety, reliability, and leak tightness.
This is required before utilizing newly installed pressure systems and ones that have been recently repaired. Pressure tests are performed to help understand the limits and capabilities of a pressure system. These components are crucial to know before putting the pipeline into service. Of course, they also help to prove that your equipment meets industry qualifications and requirements.
What is learned through a pressure test?
It&#;s important to note that pressure tests are not a matter of you should do it, but rather it's a mandatory test to comply with industry safety standards.
For more Pneumatic Test Benchinformation, please contact us. We will provide professional answers.
Pneumatic and Hydrostatic Testing
While pressure tests are mandatory, pneumatic testing is not the first option. Before considering pneumatic testing, most services will attempt performing a standard hydrostatic test. Both are viable options, but pneumatic testing is potentially more dangerous.
Hydrostatic testing indicates similar things as pneumatic testing but uses water instead of gas as the pressure testing medium. Compressed air or nitrogen can contain 200 times more stored energy for the same free volume and pressure conditions compared to water. With much higher amounts of stored energy, it is more likely to cause damage if mishandled.
Pneumatic testing is convenient and more accurate than hydrostatic testing, but the industry requires hydrostatic testing to be considered beforehand.
When Pneumatic Testing Is Utilized
In certain scenarios -- pneumatic testing becomes the only option available. While potentially dangerous, an experienced service will follow all guidelines and ensure that your equipment is not harmed.
Pneumatic testing is utilized when:
For piping systems that transport primarily gas, like natural gas pipelines, pneumatic testing would be used. Water or any other liquid would be too heavy and potentially damage the pipelines from their weight.
How Often Do You Need to Perform a Pneumatic Test?
The industry regulations require that you test your pressure system once when it is first installed and then every time after repair or alteration. If these don&#;t apply, then you don&#;t necessarily have to get them retested.
But, as mentioned before -- a leak or sudden collapse of your pressure systems can cause tremendous financial damage. That&#;s why you should get a pneumatic test done at least once a year. If applicable, keep in mind that you only have to get a pneumatic test or hydrostatic test -- not both.
Benefits of Pneumatic Testing
Even if pneumatic testing is the less used test, certain benefits should be brought to attention.
More accurate at detecting leaks - The small atomic structure of gases -- particularly helium -- allow them to pass through leaks that liquid cannot. Paired with mass spectrometry, it&#;s easy to tell if gases have leaked out of the pressure system.
No water damage - There&#;s no need to worry about the weight of water collapsing the structure of the pressure system.
Easy to clean
The accuracy is especially important if your piping or other pressure systems are sensitive to leaks. Pinpointing the location of leaks can prevent catastrophic damage before they occur.
Limitations of Pneumatic Testing
Working with gases ends up being the main cause of limitations when it comes to pneumatic testing. There would be hundreds more stored energy in compressed gases than liquid and volatile if anything were to go wrong. If an old piping system ends up collapsing during the pneumatic test, the energy is released -- causing fatal damage.
Because of this intensity, some limitations are put on pneumatic testing:
Recommended only for low-pressure applications.
Chances of equipment or pipe failure are high.
Only small segments of the piping can be tested at a time.
The damage tends to be extensive if handled improperly.
Must
be conducted by an experienced service or personnel -- this is
not
a suggestion.
Needs special attention and safety regulations -- barriers must be installed, and people cannot be working during the entirety of testing.
Before a pneumatic test can be carried out, the service will need a written justification for the pneumatic testing along with a piping schematic. While service will handle the schematic and other documentation for you, it may delay the speed at which your pressure systems can be tested.
The Precision Fabricating & Cleaning team are experts when it comes to pneumatic testing. Let us handle all of your cleaning and testing needs! Click here and contact us today!
Resources
https://www-group.slac.stanford.edu/esh/eshmanual/references/pressureProcedTest.pdf
https://www.vpgroundforce.com/gb/footer-links/useful-links/industry-resources/what-is-pressure-testing/
https://whatispiping.com/hydrotest-vs-pneumatic-test/#Types_of_Pressure_Testing
http://www.wermac.org/others/ndt_risks_pneu_testing.html
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