In manufacturing and quality control, ensuring product integrity is crucial. Even the smallest leaks can compromise performance, safety, and reliability. Helium mass spectrometer leak testing (MSLT) is a highly sensitive and effective method for detecting and locating tiny leaks in various components and systems. Developed during World War II as part of the Manhattan Project, MSLT has become an essential tool in modern industry.
Leak detection is crucial in industries such as aerospace, semiconductors, automotive, medical device manufacturing, and oil and gas. It helps maintain product quality and safety by preventing failures and contamination.
This blog post explores the fascinating world of helium leak testing, discussing techniques like sniffing, spraying, and bagging, along with their advantages, limitations, and challenges. By the end, readers will better understand how MSLT works and why it is a vital tool in modern manufacturing and quality control.
Table of Contents
Key take-a-ways
- MSLT is a critical tool for detecting and locating leaks in various components and systems, ensuring product quality and safety across industries.
- The three main MSLT techniques are sniffing, spraying, and bagging, each with its own advantages and limitations.
- The choice of MSLT technique depends on factors such as part size and geometry, required sensitivity, and available resources.
- Background helium presence in the atmosphere (5 ppm) can interfere with leak detection, particularly in the sniffing method.
- Proper removal of the test charge and potential purging with nitrogen are essential to avoid helium buildup and clinging, which can affect leak detection accuracy.
- PFC Technicians are highly qualified to perform MSLT, certified for NDT qualification per SNT-TC-1A and as Level II Inspectors, ensuring accurate and reliable leak testing results for manufacturers.
Helium leak testing techniques
When it comes to helium leak testing, there are two basic techniques that are commonly employed: sniffing and high vacuum testing. Each method has its own advantages and is suitable for different leak detection scenarios.
Sniffing
Sniffing is a technique used for detecting helium leaks down to a rate of 1×10-6mbar.l.sec. In this method, the part or component to be tested is pressurized with helium, and a specialized sniffer probe is used to manually scan the exterior of the item. The sniffer probe is connected to a helium mass spectrometer, which is capable of detecting the presence of helium in the atmosphere surrounding the test item.
The sniffing method is particularly useful for testing large components or systems that cannot be easily placed under vacuum. It is also a quick and efficient way to locate leaks in a relatively large area. However, the sensitivity of this method is limited by the presence of background helium in the atmosphere (approximately 5 ppm), which can make it challenging to detect very small leaks.
High Vacuum Testing
High vacuum testing is a more sensitive technique that allows for the detection of leaks down to a rate of 1×10 -12mbar.l.sec-1. In this method, the part or component to be tested is placed under a high vacuum, typically less than 3 mbar absolute pressure. The helium mass spectrometer is then connected directly to the vacuum chamber.
To perform the test, helium is introduced to the exterior of the test item, either by spraying or by placing the item in a helium-filled bag. If there are any leaks present, the helium will be drawn into the vacuum chamber and detected by the mass spectrometer.
High vacuum testing is the most sensitive method of helium leak detection and is ideal for testing small, delicate components or systems that require extremely low leak rates. However, it is important to consider whether the test item can withstand the high vacuum conditions required for this technique.
Definition of residual leaks
Residual leaks are leaks that occur due to imperfect seals, punctures, or other holes in a system. These leaks can be challenging to detect and locate, as they may be very small and intermittent. Residual leak detection is a crucial aspect of ensuring the integrity and performance of various components and systems.
Three types of residual leak detection methods used by PFC
PFC, a company specializing in leak detection, employs three main methods for detecting residual leaks: bagging, spraying, and sniffing. Each method has its own advantages and is suitable for different testing scenarios.
Bagged (Accumulation) Method
The bagged, or accumulation, method involves pressurizing the part to be tested with helium and then sealing it inside a container or bag. A leak detector sniffer probe is then connected to the container to sample the atmosphere inside and detect any helium that has accumulated due to leaks in the part. This method is useful for testing smaller components or those with complex geometries that may be difficult to test using other methods.
Spray Method
In the spray method, the part to be tested is evacuated to create a vacuum inside. The item under test is then connected to a leak detector, and helium is manually sprayed over the external surfaces of the part using a specialized spray gun. If any leaks are present, the helium will be drawn inside the part and detected by the leak detector. This method is particularly useful for testing larger components or systems that cannot be easily bagged or placed under vacuum.
Sniffing Method
The sniffing method involves pressurizing the part to be tested with helium to a level above atmospheric pressure. A helium sniffer gun, connected to a helium mass spectrometer, is then used to manually scan the exterior of the part. The sniffer probe samples the atmosphere at the surface of the part, detecting any helium that may be leaking out. This method is useful for quickly locating leaks in larger components or systems, as the operator can focus on specific areas where leaks are suspected.
By employing these three residual leak detection methods, PFC can effectively identify and locate leaks in a wide range of components and systems, ensuring their proper function and performance. The choice of method will depend on factors such as the size and geometry of the part, the required sensitivity, and the available resources. In the following sections, we will explore each of these methods in more detail.
Helium mass spectrometer leak testing challenges and considerations
When conducting helium mass spectrometer leak testing, several challenges and considerations must be taken into account to ensure accurate and reliable results. These factors can impact the sensitivity and effectiveness of the leak detection process, and technicians must be aware of them to mitigate their effects during testing.
One of the primary challenges in helium mass spectrometer leak testing is the presence of background helium in the Earth's atmosphere, at approximately 5 parts per million (ppm). This background helium can interfere with leak detection, particularly when using the sniffing method, making it difficult for the helium mass spectrometer to distinguish between actual leaks and ambient helium.
To minimize this impact, testing should be conducted in a well-ventilated area, using appropriate techniques such as shielding the test area or using a high-quality sniffer probe with a low detection limit. In some cases, alternative leak detection methods, such as the bagged or spray methods, may be necessary during helium mass spectrometer leak testing.
Another important consideration in helium mass spectrometer leak testing is the proper removal of the test charge after the leak detection process is complete. If the helium used for testing is not properly removed or vented, it can accumulate in the testing area, leading to a buildup of background helium over time.
This buildup can reduce the sensitivity of the process and make it increasingly difficult to detect small leaks. To avoid helium buildup, the test charge must be properly vented or removed after each leak detection procedure, using specialized equipment or allowing the helium to dissipate in a well-ventilated area.
Additionally, helium can cling to the surfaces of the test item or the testing equipment, interfering with reducing the sensitivity of the helium mass spectrometer. To remove clinging helium, purging the test item or the testing equipment with gaseous nitrogen (GN2) may be necessary. This purging process helps to flush away any residual helium, ensuring the process remains accurate and sensitive.
By understanding and addressing these challenges and considerations, technicians can ensure that helium mass spectrometer leak testing is conducted effectively and efficiently, providing reliable results and helping to maintain the integrity and performance of the tested components and systems during helium mass spectrometer leak testing.
Leak testing limits
Understanding the limits of each helium leak testing method is crucial for achieving accurate results. The maximum achievable lower detection limit depends on factors such as the sensitivity of the helium mass spectrometer, background helium presence, and the specific testing technique used.
The sniffer probe method, which involves scanning a pressurized part with a sniffer probe connected to a helium mass spectrometer, has a maximum achievable lower detection limit of 1×10-6 mbar. This limit is primarily due to the presence of background helium in the Earth's atmosphere (approximately 5 ppm), which can interfere with detecting very small leaks.
In contrast, the spray and bagged methods, involving either spraying helium over an evacuated part's surfaces or sealing a pressurized part inside a container, have a maximum achievable lower detection limit of 1×10-10 mbar. These methods are less affected by background helium, as the test item is under vacuum or sealed in a controlled environment, allowing the helium mass spectrometer to detect much smaller leaks.
It's important to note that these limits are theoretical maximums and may not always be achievable in practice due to factors such as the condition of the test item, operator skill, and interfering substances.
Conclusion
In this blog post, we explored three main helium leak testing techniques: sniffing, spraying, and bagging. Each method has its advantages and limitations, and the choice depends on factors such as part size and geometry, required sensitivity, and available resources.
Understanding the challenges and limitations of helium mass spectrometer leak testing (MSLT), such as background helium presence, proper test charge removal, and potential purging with nitrogen, is crucial for accurate and reliable results. Technicians can optimize the leak detection process by addressing these factors.
Leak detection is critical for ensuring product quality, reliability, and safety across industries like aerospace, industrial, medical devices, and chemical plants. It helps prevent failures, minimize downtime, and protect human lives and expensive assets.
PFC Technicians are uniquely qualified to perform helium leak testing, certified for NDT qualification per SNT-TC-1A and as Level II Inspectors.
By relying on their expertise and implementing robust leak testing procedures, manufacturers can maintain the highest quality and performance standards, building customer trust, protecting brand reputation, and ensuring long-term success.
Contact PFC today to learn more about how our helium mass spectrometer leak testing capabilities can cost-effectively augment your quality programs.