Leak testing of helium permeable parts presents unique challenges in production environments. Many products made from plastics, elastomers, or thin films allow helium to permeate directly through the material. As a result, engineers must design leak tests that distinguish between true leaks and normal helium permeation.
This article explains how manufacturers can successfully perform leak testing of helium permeable parts when helium remains the best tracer gas for the required sensitivity.
Why Leak Testing of Helium Permeable Parts Is Challenging
Helium is widely used in production leak testing because it enables very high sensitivity. Many applications require detection limits below 1 × 10⁻³ atm·cc/sec, where air-based methods often fall short.
However, helium permeates easily through many plastics and elastomers. When helium passes through the wall of a test part, it creates background helium that can resemble a leak signal. Without proper test design, permeation can mask real defects or create false failures.
When Helium Is Still the Right Tracer Gas
In some cases, manufacturers can switch to an alternate tracer gas or use air leak testing. However, many products still demand helium due to tight leak rate requirements.
When helium remains necessary, engineers must account for both:
- Helium permeation rate
- Permeation time constant
Understanding these two factors allows the test system to separate permeation effects from physical leaks.
Designing Leak Testing of Helium Permeable Parts
Engineers can use two primary strategies for leak testing of helium permeable parts.
Method 1: Background Subtraction
If permeation remains consistent from part to part and stays below the reject limit, the test system can subtract the steady-state helium background from the total signal. This approach works best when the permeation time constant fits within the production cycle time.
Method 2: Permeation Rate Analysis
When background subtraction is not reliable, the test can focus on how the helium signal changes over time. Physical leaks produce a different signal profile than permeation. By analyzing the rate of helium increase, the system can identify true leaks even in permeable materials.
Example: High-Permeation Plastic Containers
Some pharmaceutical-grade PTFE storage containers exhibit steady-state helium permeation rates around 1 × 10⁻⁴ atm·cc/sec at a defined fill pressure. Using advanced test methods such as hybrid accumulation techniques, engineers can still achieve reject limits as low as 1 × 10⁻⁵ atm·cc/sec.
This approach allows accurate leak testing of helium permeable parts without sacrificing sensitivity.
Summary: Reliable Leak Testing of Helium Permeable Parts
Leak testing of these parts requires careful system design, but it remains achievable. By understanding permeation behavior and selecting the correct test strategy, manufacturers can successfully distinguish between material permeation and true leaks.
With proper engineering, helium remains a viable tracer gas for high-sensitivity leak testing—even for permeable products.
References
• Application Note 01-03 Helium Leak Testing Flexible Wall Parts
• Technical Note A: Production Leak Testing: What, Why, and How
