Free ASNT NDT Level III Leak Testing (LT) Examination Practice Questions

Sample Practice Questions

Try these 10 sample questions from the ASNT NDT Level III Leak Testing (LT) Examination practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1During a leak test, an engineer reports the amount of gas passing through an opening per unit time. What property is being reported?

   1. A.Gas conductance
   2. B.Leakage rateCorrect answer: B
   3. C.Pumping speed
   4. D.Differential pressure

   Explanation: ASNT describes leakage rate as "The amount of gas or liquid passing through a leak over time. Leak testing measures flow, not the size of the hole itself." The measured quantity is therefore the leakage rate.

   Reference: Leak Testing (LT): NDT Methods for Sealed System Integrity — How Leak Testing Works: Basic Principles, Leakage Rate

2. 2A leak-test procedure calls for an ASTM practice covering bubble emission techniques. Which designation should the Level III consult?

   1. A.ASTM E1002
   2. B.ASTM E1003
   3. C.ASTM E515Correct answer: C
   4. D.ASTM E908

   Explanation: ASTM lists "E515-11(2022) Standard Practice for Leaks Using Bubble Emission Techniques" under leak testing. The other designations refer to other leak-testing practices.

   Reference: Nondestructive Testing Standards — Leak Testing Method, E515-11(2022)

3. 3A technician selects a tracer for a halogen diode leak detector. Which gas type is appropriate for this technique?

   1. A.Helium
   2. B.Nitrogen
   3. C.Hydrofluorocarbon refrigerantCorrect answer: C
   4. D.Carbon dioxide

   Explanation: ASNT says the technique "Uses a halogen-based tracer gas, such as a refrigerant, introduced into the system being tested." A hydrofluorocarbon refrigerant contains a halogen and is the appropriate tracer among these choices.

   Reference: Leak Testing (LT): NDT Methods for Sealed System Integrity — How Leak Testing Is Conducted in NDT, Advanced LT Techniques, Halogen Diode Leak Testing

4. 4A helium leak rate is reported as 2.00 standard cm³/s at 0 °C and 101,325 Pa. Using NIST's conversion, what is the equivalent molar flow rate?

   1. A.2.225e-5 mol/s
   2. B.4.45e-5 mol/s
   3. C.8.90e-5 mol/sCorrect answer: C
   4. D.8.90e-6 mol/s

   Explanation: NIST says "When referenced to the specific temperature, std. cm3/s can be converted to mol/s by multiplying by 4.45 x 10-5." Multiplying 2.00 by 4.45 × 10⁻⁵ gives 8.90 × 10⁻⁵ mol/s.

   Reference: Leak Artifacts — Leak Artifacts, standard conditions and conversion note

5. 5An NDT report must permit an individual pressure gauge to be traced to its calibration record. Which recorded identifier distinguishes that particular gauge?

   1. A.The gauge's model number
   2. B.The gauge's serial numberCorrect answer: B
   3. C.The gauge's measuring range
   4. D.The gauge's manufacturer

   Explanation: ASNT says: "The report must include the manufacturer, model, and serial number information in such a manner that each individual piece of equipment can be traced from the report." The serial number identifies the individual gauge.

   Reference: Nondestructive Testing Report Writing: Back to Basics — Recording Equipment and Materials

6. 6A leak-test procedure uses a liquid film to examine a vessel that cannot be pressurized and is accessible from only one side. Which attachment does ASTM E515 describe for that application?

   1. A.An accumulation hood
   2. B.A vacuum boxCorrect answer: B
   3. C.A detector probe
   4. D.A pressure enclosure

   Explanation: ASTM states: "It can be used with a vacuum box to test vessels which cannot be pressurized or where only one side is accessible." The vacuum box creates the test condition at the accessible surface.

   Reference: Standard Practice for Leaks Using Bubble Emission Techniques — ASTM E515-11(2022), section 6.2

7. 7A Level III writes the acceptance criterion in a leak-test specification for a component. Which parameter directly establishes the allowable leakage?

   1. A.The maximum system leak rateCorrect answer: A
   2. B.The system test duration
   3. C.The system test pressure
   4. D.The tracer gas concentration

   Explanation: ASTM states: "Acceptance is based on the maximum system allowable leakage." A maximum permissible leak rate directly defines the acceptance limit.

   Reference: Standard Practice for Leakage Measurement Using the Mass Spectrometer Leak Detector or Residual Gas Analyzer in the Hood Mode — ASTM E1603/E1603M-11(2022), section 5.1

8. 8A leak-testing employee assesses a permit-required confined space under OSHA's general-industry standard. Below what oxygen concentration is the atmosphere defined as oxygen deficient?

   1. A.16.0 percent by volume
   2. B.19.5 percent by volumeCorrect answer: B
   3. C.20.9 percent by volume
   4. D.23.5 percent by volume

   Explanation: OSHA defines an "Oxygen deficient atmosphere means an atmosphere containing less than 19.5 percent oxygen by volume." The stated boundary is 19.5 percent.

   Reference: Permit-required confined spaces — 29 CFR 1910.146(b), definition of oxygen deficient atmosphere

9. 9A rigid, sealed test vessel contains an ideal gas at an absolute pressure of 100 kPa and a temperature of 300 K. If its gas temperature rises to 600 K while its volume and gas amount remain constant, what is its final absolute pressure?

   1. A.50 kPa
   2. B.100 kPa
   3. C.200 kPaCorrect answer: C
   4. D.400 kPa

   Explanation: NIST gives the ideal-gas relationship as "PV=NRT". With volume and gas amount fixed, absolute pressure is proportional to absolute temperature. Doubling the temperature doubles the pressure from 100 kPa to 200 kPa.

   Reference: NIST Leak Calibration Service — Appendix D, Low-range flowmeters for use with vacuum and leak standards, section I

10. 10Under ASTM E499/E499M, which method captures escaping tracer gas in an enclosure to build a detectable signal above the background?

    1. A.Direct probing
    2. B.Tracer probing
    3. C.AccumulationCorrect answer: C
    4. D.Hood testing

    Explanation: ASTM states: "6.2 Test Method B is used to increase the concentration of trace gas coming through the leak by capturing it within an enclosure until the signal above the helium background can be detected." It identifies "1.2.2 Test Method B—Accumulation." as that method.

    Reference: Standard Practice for Leaks Using the Mass Spectrometer Leak Detector in the Detector Probe Mode — ASTM E499/E499M-11(2025), sections 1.2.1–1.2.2 and 6.2