NDT - Non-Destructive Testing Leak Testing Techniques Questions and Answers

Question 1

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?

Accepted Answer

Helium mass spectrometer testing

Answer

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.

Question 2

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

Accepted Answer

Low background concentration in the atmosphere

Answer

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.

Question 3

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?

Accepted Answer

Detector probe technique

Answer

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.

Question 4

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?

Accepted Answer

Entrapped air from the initial application of the solution

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

NDT - Non-Destructive Testing Practice Test

NDT - Non-Destructive Testing Practice Test

NDT - Non-Destructive Testing Leak Testing Techniques Questions and Answers