At CTS, we help you get the most accurate, reliable leak test results and reach your production goals. We also take pride in helping our customers better understand their leak test processes. We often host webinars and in-person seminars to share general leak testing knowledge, but also to give manufacturers the chance to ask questions.
Here are some of the top questions our most recent attendees asked our team—sharing the answers here for everyone’s benefit!
1. What are the pros and cons of converting from helium to forming gas?
Answer: Many manufacturers choose to use forming gas instead of helium for tracer gas leak testing. The most popular alternative is forming gas, typically a mixture of 5% hydrogen and 95% nitrogen. Typically, helium is best to identify and locate very low leak rates—lower than 1E-4 scc/s. Since it only has trace presence in our atmosphere, which makes it easier to control background.
However, given its popularity, it has become prone to scarcity and supply issues, which leads to higher costs and potential unavailability for manufacturers. This has led manufacturers that don’t require helium to meet their specifications to opt for forming gas as a more cost-effective and easier-to-obtain alternative.
Read the blog post for more details to help you choose →
2. What are the main reasons why helium is still required when hydrogen seems like a much cheaper option?
Answer: While forming gas (a hydrogen mixture) can be used as a more cost-effective option for tracer gas leak testing, there are still some test scenarios where helium is best. For example, if you are testing to extremely small leak rates (lower than 1E-4 scc/s), it is necessary to use helium (or a mixture of helium/nitrogen), as trace amounts of hydrogen can be present in a production environment, which will make it impossible to accurately identify leaks that small.
Desired cycle time can also be a consideration, as forming gas takes longer to test because of the smaller concentration rate of rise. Depending on the size of your part and the relative test chamber, you may not be able to meet your target cycle time using forming gas, leaving helium as your best option.
Learn more about the pros and cons of forming gas vs. helium →
3. How is a sniff leak test qualified? How reliable are results?
Answer: If you are using a mass spectrometer, it will give you a good, accurate value at the exact spot you’re sniffing. BUT a general challenge with sniff leak testing is that it’s not able to differentiate if you’re sniffing an actual leak or background (environment). Also, there’s not a great way to get a total leak rate from a part solely using the sniff method—it is most often used as a leak location in assembly, test, and rebuild processes.
Learn more about sniff leak testing →
4. What if my part can’t handle hard vacuum purging to exhaust test gas after the test?
Answer: If your part can’t handle hard vacuum purge to pull out air before the test and to exhaust helium tracer gas after a test, whether it’s due to the part materials or design stability, etc., you can also purge using flow. To do this effectively during the fill sequence, you will flow the trace gas through the device allowing it to exhaust to an external exhaust passageway, then valve the exhaust closed while circulating the trace gas through the part to equalize the concentration of the gas after a set amount of time. Nitrogen can be used nicely for this process.
5. What is the best way to control for ambient background during test?
Answer: First, generally, choosing a 100% potency tracer gas will offer the clearest signal to noise ratio, and thus the best measurement accuracy. However, the ideal test medium will ultimately depend on the size of your part, your leak rate, the application, and your present environment.
Designing your test with an enclosure is also a very effective way to control background. Nitrogen purge technology or accumulation tracer gas systems are both good options to consider for this kind of requirement. However, as always, it will depend on your specific specifications and application—we are happy to discuss your specific application! Contact us anytime.
6. How do you measure leak rates through materials in the range of 1E-06 mbar L/s and smaller using helium gas?
Answer: The only way to get to those levels is to use helium hard vacuum mass spec testing and having an extremely efficient vacuum system to pull vacuum in your chamber to levels where that measurement is possible.
Generally, leak detection systems, when testing low leak rates, will have a hard time differentiating between a permeation flow through material vs. an actual leak, which makes this kind of testing particularly challenging when you are testing certain materials that permeate helium. Options could include measuring the leak very quickly before the permeation occurs, or testing the part only one time since it will be saturated with helium after its first test.
Contact us to discuss the best options for your application →
7. Can a nitrogen/helium gas mixture be used with hard vacuum testing and how does it affect the testing in regard to cycle time, accuracy, and resolution?
Answer: Yes, you can! However, any level of mixture will affect all of the above metrics. The higher the helium concentration, the better. You can use a lower concentration, as long as your cycle time, repeatability, and leak rate has been reduced (calculated based on the lower percentage of helium as an equal amount). The ideal allowable mixture will be specific to your application and specifications. Our team would be happy to help you identify your ideal gas mixture. Contact us!
8. For high pressure systems with large volumes and tight leak rates, what's the best trace gas to use?
Answer: Likely, forming gas is the best option (typically a mixture of 5% hydrogen and 95% nitrogen), if you’re able to do a sniff test. Though you may run into challenges if your leak rate is too small, you’ll be forced to use helium as your trace gas. Though using helium is often more expensive, utilizing a helium reclaim system becomes very efficient with high pressure applications, or you may also be able to use a split concentration of helium/nitrogen to get to those levels of leak rate measurement.
9. What is a good way to determine the proper mixture of tracer gases?
Answer: 100% tracer gas will always be best. This will give the highest signal to noise ratio for the highest measurement accuracy and fastest cycle time.
Some manufacturers may try to reduce consumption costs by reducing this ratio, adding a certain quantity of air or nitrogen to the mixture. But remember, you only want to go as low as your sensitivity allows, which is a function of your leak rate, cycle time, and performance requirements. Unfortunately, there is no one-size-fits-all answer for this ratio, but feel free to contact our team to do the calculations for your test!
10. Is it possible to build a helium recovery system into a machine test chamber?
A: Yes, absolutely. CTS offers a variety of standard and modular helium recovery systems, as well as design-build options for custom, built-in needs. Helium recovery can recycle up to 95% of helium, so they are a great way to reduce consumption costs and boost your cost efficiency!
Click here to calculate your capacity and potential ROI →
Do you have other questions for our team? Contact us. We’re to help!
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