About Leak Testing (LT)

Leak Testing is used to detect through leaks using one of the four major LT techniques: Bubble, Pressure Change, Halogen Diode and Mass Spectrometer Testing.

• Bubble Leak Testing relies on the visual detection of a gas (usually air) leaking from a pressurized system; Pressure Change Leak Testing can be performed on closed systems only-- detection of a leak is done by either pressurizing the system or pulling a vacuum then monitoring the pressure. 
• Halogen Diode Leak Testing is done by pressurizing a system with a mixture of air and a halogen-based tracer gas-- after a set period of time, a halogen diode detection unit, or "sniffer", is used to locate leaks. 
• Mass Spectrometer Leak Testing can be done by pressurizing the test part with helium or a helium/air mixture within a test chamber then surveying the surfaces using a sniffer, which sends an air sample back to the spectrometer.

Topical Outline

This examination is 4 hrs in length, having 135 questions of equal value.

1. Principles theory
   • Physical principles in leak testing
   • Principles of gas flow
   • Proper selection of LT as method of choice
2. Equipment/Material
   • Leak testing standards
   • Detector/instrument performance factors
   • Vacuum pumps
   • Bubble testing practices and techniques
   • Absolute pressure testing equipment
   • Absolute pressure hold testing of containers
   • Absolute pressure leakage rate testing of containers
   • Analysis of data for determination of accurate results
   • Halogen testing equipment
   • Helium mass spectrometer testing equipment
3. Technique/Calibration
   • Bubble test
   • Pressure change/measurement test
   • Halogen diode detector leak test
   • Mass spectrometer leak testing
   • Helium mass spectrometer vacuum testing by dynamic method
   • Helium mass spectrometer vacuum testing by static method
4. Interpretation/Evaluation
   • Basic techniques and/or units
   • Test materials and equipment effects
   • Effects of temperature and other atmospheric conditions
   • Calibration for testing
   • Probing/scanning or measurement/monitoring
   • Leak interpretation evaluation
   • Acceptance and rejection criteria
5. Procedures
6. Leak testing procedures
7. Leak testing specifications
8. Safety and Health
   • Safety considerations
   • Safety precautions
   • Pressure precautions
   • Safety devices
   • Hazardous and tracer gas safety
   • Types of monitoring equipment
   • Safety

References

The number in parentheses following each reference is the ASNT catalog number.

• NDT Handbook: Volume 1, Leak Testing (141, 141CD, 141WCD)
• ASNT Level III Study Guide — Leak Testing Method (2266)
• All Four Leak Testing Methods - Supplement to Recommended Practice No. SNT-TC-1A (Q&A Books) — Leak Testing Methods (2033A)