Leak Testing Techniques Flashcards

A technician must verify the integrity of a hermetically sealed electronic component for a deep-space satellite, where even a minuscule leak is unacceptable. Which of the following leak testing methods offers the highest sensitivity for this application?

Answer: Helium mass spectrometer testing

Helium mass spectrometer testing is the most sensitive practical leak detection method available, capable of detecting extremely small leaks (down to 10-12 mbar·l/s). This level of sensitivity is critical for high-reliability applications like space hardware where leakage cannot be tolerated.

When selecting a tracer gas for leak testing, which of the following is a critical property for ensuring high sensitivity and minimizing false readings?

Answer: Low background concentration in the atmosphere

A good tracer gas should be rare in the atmosphere to provide a high signal-to-noise ratio, making it easier to detect leaks without interference from ambient air. Helium is often used because its atmospheric concentration is very low (about 5 ppm), which prevents high background signals from masking a true leak.

An inspector is performing a leak test on a large vessel that has been pressurized with a helium-air mixture. The inspector moves a probe connected to a mass spectrometer over the exterior surface of the vessel to pinpoint the location of any leaks. What is this specific technique called?

Answer: Detector probe technique

This method is the detector probe technique, commonly known as "sniffing." It involves pressurizing the component with a tracer gas and using a detector probe on the outside to find where the gas is leaking out. The tracer probe technique is the opposite, where a vacuum is pulled on the component and tracer gas is sprayed on the exterior.

During a bubble leak test using a soap solution on a pressurized gas line, the technician observes a single, large bubble that forms immediately upon application and then remains without growing or bursting. What is the most likely interpretation of this observation?

Answer: Entrapped air from the initial application of the solution

A true leak will produce a continuous stream of bubbles or a bubble that steadily grows. A single, static bubble that forms immediately is often just air trapped under the solution as it was applied, not an indication of a leak from the pressurized system.

Which of the following is a standard unit used to express a leak rate, representing a throughput of gas?

Answer: Atmosphere cubic centimeters per second (atm·cm³/s)

A leak rate is defined as the throughput of gas through a leak, which accounts for volume, pressure, and time. Standard units like atm·cm³/s (also written as atm·cc/s) or the SI unit Pa·m³/s incorporate all three components. The other options are units of pressure change, simple volumetric flow, or pressure change over a long period, not standard leak rate units.

Which of the following leak testing methods relies on monitoring the change in pressure inside a sealed component over a specified period to determine if a leak is present?

Answer: Absolute pressure testing

Absolute pressure testing, a type of pressure change measurement, directly measures the internal pressure of a sealed object over time. A drop in pressure (for a pressurized object) or a rise in pressure (for an evacuated object) indicates a leak. The other methods rely on detecting a specific tracer gas (halogen, helium) or the formation of bubbles.