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The 10 Most Common Errors in Leak Testing | 2016-08-01

Dec. 16, 2024

The 10 Most Common Errors in Leak Testing | -08-01

The smallest leak in a component or sub-assembly can compromise a product's performance and ultimately your company's reputation. Product integrity is vital. Providing customers with a quality product that they can trust for reliability and safety positively impacts a company's bottom line.

SUNCENTER supplies professional and honest service.

Industrial leak testing and leak detection are complex issues, notes Sandra Seitz, automotive market manager at INFICON. An appropriate test method must be carefully selected, and choosing the correct method for a specific application depends on many factors. Sensitivity is essential, as is the marginal leak rate of the method used, along with the cycle times achievable on the production line.

Process repeatability and reliability must also be considered, alongside capital expenditures and operating costs, all of which are based on the particular test method employed.

Each year, manufacturers conduct over a billion leak tests on critical components, but various factors can hinder successful outcomes. The top 10 mistakes that can impede effective product leak testing include:

ERROR 1: USING THE WRONG LEAK-DETECTION METHOD

Using the bubble test method can often lead to incorrect conclusions. If no bubbles are observed, it is assumed there is no leak. The tester may believe what they do not see and thus feel satisfied with the results.

Evaluating whether a leak detection method is suitable for a particular application should take its leak rate into account. Regrettably, this fundamental rule is often overlooked. For instance, plastic components might be tested using pressure decay methods, neglecting their deformability and changes in volume due to compressed air. Moreover, the performance of an integral leak test must align with subsequent leak detection methods. Sometimes the integral leak test occurs in a helium chamber, yet leak localization employs the bubble test method instead of a more precise sniffer leak detection method with tracer gas.

ERROR 2: TESTING AT THE WRONG POINT IN TIME IN THE PRODUCTION PROCESS

Careful consideration is essential when selecting the optimal moment in the production process for a leak test. Testing individual subcomponents for leaks before assembly often proves beneficial. For instance, confirming the tightness of a transmission case prior to assembly could prevent wasted effort if the housing fails during final testing.

ERROR 3: TESTING A CONTAMINATED PART

For almost all test methods, leak tests should always occur on new, unused test pieces. If a component has been in operation or has been filled with oil or water, there is a risk that small leaks could be clogged.

Castings may also retain cutting-oil residues after machining. Before conducting a leak test, the test piece must be thoroughly cleaned and subsequently dried to prevent any cleaning fluid from obstructing potential leaks.

ERROR 4: IGNORING TEMPERATURE CHANGES

Temperature fluctuations seriously impact integral leak tests, particularly those using pressure decay or differential pressure measurement. Even minor temperature changes can significantly alter the measurable leak rate. The size of a leak is also influenced by rises in temperature and the material's expansion behavior. For example, in exhaust gas coolers, leaks may only manifest when the component reaches its typical operating temperature, prompting some manufacturers to conduct these tests in climate-controlled chambers.

ERROR 5: FLUCTUATING TEST PRESSURES

To reliably and reproducibly determine leak rates, it is crucial to maintain a constant pressure when filling the test piece, even when utilizing tracer gas methods. Automated tracer gas filling systems can help achieve this consistency. In certain instances, effective filling requires prior evacuation. Heat exchangers, which often consist of lengthy tube systems, require careful attention; if tracer gas is introduced, it may inadvertently increase the pressure inside the test piece. Only after evacuation can the tracer gas adequately reach all potential leaks. Furthermore, to reduce testing costs, some tests utilize helium tracer gas at a mere 1 percent concentration, necessitating meticulous distribution of the gas.

ERROR 6: FILLING WITH A TEST GAS WITHOUT PREVIOUS EVACUATION

It is mandatory to evacuate the test part before filling it with tracer gas, particularly for long and narrow geometries. Failing to evacuate beforehand can cause the air in the test part to be pushed to the geometry's end, preventing tracer gas from reaching that area. Potential leaks would release the trapped air, evading detection by the tracer gas leak detector.

Evacuation is critical, particularly when filling the part with low tracer gas pressures, as trapped air can dilute the gas concentration. For example, if a test part is filled with air at atmospheric pressure and subsequently filled with tracer gas, the resulting concentration may only be 50 percent due to dilution.

ERROR 7: NOT KNOWING WHAT YOU ARE TESTING

Utilizing a reproducible measurement method for integral leak tests is a significant improvement over relying on subjective assessments by human testers. Understanding what is being measured and which test medium is employed is crucial. Occasionally, leak rates specified for air do not directly apply to helium, which possesses a slightly higher dynamic viscosity. Correct conversion data must be used when interpreting these values.

When measuring the leak rate in grams per year for an air conditioning unit with an integral leak test, it is essential to remember that the helium measuring instrument may indicate a flow in mbar·l/s. Devices that perform automatic conversions exist, with exact conversion factors derived from the refrigerant's molecular weight.

If testing with diluted helium mixtures for budget reasons, it is important to account for the varying measurable helium concentrations when evaluating leak rate results. Moreover, tightness requirements apply to specific operating pressures, necessitating adjustments if the test occurs at pressures that deviate from the piece's later operating pressure.

Equating a leak rate with gas concentration readings stated as parts per million (ppm) is also a significant error. Concentration reflects a temporary condition, indicating the presence of particles at a specific moment, whereas leak rate determines the volume flow through a leak.

ERROR 8: UNDERESTIMATING STRINGER LEAKS AND GROSS LEAKS

Stringer leaks, resembling capillary-like corridors, can pose serious risks for airbag manufacturers. The time required for helium tracer gas to distribute before emerging from stringer leaks must be considered. Working with very short intervals between filling and testing may make the identification of stringer leaks difficult or impossible.

Conversely, gross leaks involve helium escaping the test piece prior to the actual test interval, leading to concurrent evacuation of the vacuum test chamber and the helium inside the test piece. Integrating a simple pressure decay test within the tracer gas system can assist in detecting gross leaks before filling the test piece with helium.

ERROR 9: NEGLECTING TEST SYSTEM MAINTENANCE

If leak rates are not measured on a test station for days or weeks, it may mean one of two things: either production quality is exceptional, or the test system is not functioning correctly.

Leaking tracer gas lines can obscure accurate measurements. All interconnection points, hoses, and test piece brackets must undergo regular inspections. Misrepair of tracer gas systems can be a problem as well. For example, wrapping an interconnection point in Teflon tape for sealing can lead to helium escaping through the porous material, resulting in accuracy and cost issues.

Regularly checking the accuracy of the system using a reference leak, with a consistent leak rate, allows for identification of any test setup errors. Using glass capillaries as test leaks is preferable for maintaining a defined leak rate. Less robust test leaks made of metal can vary significantly based on temperature and pressure, making glass capillaries more suitable for precise testing. System accuracy checks, especially with calibration leaks, can prevent critical issues, such as connecting a helium bottle instead of an oxygen one.

Contact us to discuss your needs regarding pressure testing machines. Our experienced sales team can assist you in identifying the options that best suit your requirements.

ERROR 10: DOING THINGS YOURSELF

In the realm of industrial leak testing and leak detection, consulting with experts is essential. Choosing the appropriate test method tailored to a specific application, configuring the system correctly, and ensuring a foolproof review process are all critical, albeit challenging tasks.

Again, seek professional support. If you aim to guarantee the integrity of your production and avoid costly product recalls, merely stating that you perform checks is insufficient. A negative test does not assure compliance with the established requirements. Assurance of quality only comes from reliable test methods and processes.

The objective is to perform accurate measurements correctly and consistently at every level, every day.

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