NDT Leak Testing Techniques 2 — Questions and Answers
Question 1: Which leak testing method is most appropriate for detecting very small leaks in hermetically sealed electronic packages?
- Hydrostatic pressure testing
- Helium mass spectrometer leak testing (Correct answer)
- Bubble immersion testing
- Dye penetrant testing
Correct answer: Helium mass spectrometer leak testing
Helium mass spectrometer leak testing is the most sensitive method available and is widely used for hermetically sealed electronic components.
Question 2: In tracer gas leak testing, what property of helium makes it the preferred tracer gas?
- High molecular weight and reactivity
- Low background concentration in air and small atomic size (Correct answer)
- High density and solubility in water
- Flammability and ease of detection
Correct answer: Low background concentration in air and small atomic size
Helium's very low natural atmospheric concentration (~5 ppm) and small atomic size allow it to pass through tiny leaks and be detected at very low levels.
Question 3: What does the term 'minimum detectable leak rate' refer to in leak testing?
- The largest leak a detector can sense
- The smallest leak rate that a detector can reliably identify above background noise (Correct answer)
- The average leak rate across all test samples
- The leak rate that causes immediate system failure
Correct answer: The smallest leak rate that a detector can reliably identify above background noise
Minimum detectable leak rate is the smallest leak signal that can be distinguished from background noise with acceptable confidence.
Question 4: A pressure decay test shows a steady pressure drop over time. What is the most likely cause?
- Temperature increase in the test environment
- A leak allowing gas to escape the test volume (Correct answer)
- Gauge calibration drift only
- Normal elastic deformation of the test part
Correct answer: A leak allowing gas to escape the test volume
Steady pressure decay in a closed system is a primary indicator of a leak allowing gas to escape.
Question 5: Which standard governs leak testing methods for pressure-containing equipment in the United States?
- ASTM E515
- ASME Boiler and Pressure Vessel Code Section V (Correct answer)
- AWS D1.1
- API 570
Correct answer: ASME Boiler and Pressure Vessel Code Section V
ASME BPVC Section V, Article 10 specifically addresses leak testing methods for pressure-retaining equipment.
Question 6: In vacuum leak testing, a helium sniffer probe is used to detect leaks by:
- Applying vacuum inside the part while sniffing outside for helium escaping inward
- Pressurizing the part with helium while sniffing the exterior for leaking helium (Correct answer)
- Immersing the part in helium liquid and observing bubbles
- Measuring the change in vacuum level inside the detector
Correct answer: Pressurizing the part with helium while sniffing the exterior for leaking helium
In the sniffer (pressurization) method, the part is filled with helium under pressure and the exterior is scanned with a sniffer probe to detect escaping helium.
Question 7: What is the primary advantage of using a halogen leak detector over a bubble test?
- It is less expensive and requires no training
- It provides quantitative leak rate measurement and higher sensitivity (Correct answer)
- It can only detect leaks in liquid systems
- It eliminates the need for pressurizing the test part
Correct answer: It provides quantitative leak rate measurement and higher sensitivity
Halogen detectors offer much higher sensitivity than bubble tests and can provide quantitative leak rate data.
NDT Leak Testing Techniques 2
Which leak testing method is most appropriate for detecting very small leaks in hermetically sealed electronic packages?