NDT Leak Testing Techniques 3 — Questions and Answers
Question 1: During a hydrostatic leak test, why is it important to vent all air from the system before pressurizing?
- Air increases corrosion inside the component
- Trapped air can compress and store energy, creating a potential explosion hazard (Correct answer)
- Air reacts with water to produce harmful gases
- Air reduces the sensitivity of the pressure gauge
Correct answer: Trapped air can compress and store energy, creating a potential explosion hazard
Unlike water, trapped air compresses under pressure and stores energy that can cause a violent failure if a rupture occurs.
Question 2: Which leak testing technique is classified as a 'through-wall' method?
- Visual inspection
- Acoustic emission monitoring (Correct answer)
- Thermal imaging
- Magnetic particle testing
Correct answer: Acoustic emission monitoring
Acoustic emission detects stress waves generated by active leaks passing through the wall of a structure, making it a through-wall technique.
Question 3: What effect does temperature have on pressure decay leak testing results?
- Temperature has no effect on gas pressure in a closed volume
- Temperature increases cause pressure increases, which can mask or simulate leaks (Correct answer)
- Higher temperature always decreases pressure in sealed systems
- Temperature only affects liquid leak tests, not gas leak tests
Correct answer: Temperature increases cause pressure increases, which can mask or simulate leaks
Per the ideal gas law, rising temperature increases pressure in a sealed system, which can mask actual leaks or simulate false positives during pressure decay tests.
Question 4: What is the purpose of a 'reference leak' in a mass spectrometer leak test setup?
- To create a controlled baseline for verifying detector sensitivity and calibration (Correct answer)
- To introduce a known defect for training purposes only
- To reduce the background helium signal to zero
- To determine the maximum allowable leak rate for the component
Correct answer: To create a controlled baseline for verifying detector sensitivity and calibration
A reference (calibrated) leak provides a known leak rate to verify that the mass spectrometer system is responding correctly and is properly calibrated.
Question 5: In which industry is the 'bombing' or pressurization method of helium leak testing most commonly used?
- Oil and gas pipeline inspection
- Aerospace and electronics hermetic package testing (Correct answer)
- Civil infrastructure bridge inspection
- Nuclear reactor core inspection
Correct answer: Aerospace and electronics hermetic package testing
The helium bombing method is widely used in aerospace and electronics to test hermetically sealed packages for micro-leaks.
Question 6: What does a 'gross leak' mean in the context of NDT leak testing?
- A leak that is aesthetically unpleasant but functionally harmless
- A relatively large leak detectable by less sensitive methods such as bubble or soap solution tests (Correct answer)
- A leak causing immediate catastrophic failure
- A leak visible only under magnification
Correct answer: A relatively large leak detectable by less sensitive methods such as bubble or soap solution tests
A gross leak is a large-rate leak detectable by simple methods, as opposed to fine leaks that require highly sensitive instrumentation.
Question 7: Why must leak testing personnel be qualified and certified for NDT applications?
- Certification is only required for managers, not technicians
- Proper training ensures correct test setup, interpretation, and reliable results that protect safety (Correct answer)
- Certification is a regulatory formality with no impact on test quality
- Only the equipment manufacturer needs to be certified
Correct answer: Proper training ensures correct test setup, interpretation, and reliable results that protect safety
Qualified personnel correctly apply test parameters, interpret results, and identify rejectable conditions, directly impacting safety and quality outcomes.
NDT Leak Testing Techniques 3
During a hydrostatic leak test, why is it important to vent all air from the system before pressurizing?