G3 Leak Detection and Testing Procedures 1 — Questions and Answers
Question 1: Which leak detection method is most commonly used for a quick field check of gas piping joints?
- Electronic combustible gas detector
- Soap bubble solution applied to joints (Correct answer)
- Pressure gauge monitoring over time
- Ultraviolet dye injection
Correct answer: Soap bubble solution applied to joints
Soap bubble solution is the standard field method for locating gas leaks at joints and fittings, as bubbles form visibly where gas escapes.
Question 2: Before applying pressure for a leak test on a new gas piping installation, what must a technician ensure?
- All appliances are turned on to full capacity
- All open ends are capped and appliance connections are isolated (Correct answer)
- The gas meter is fully open
- The main shutoff valve is open
Correct answer: All open ends are capped and appliance connections are isolated
All open ends must be capped and appliance connections isolated to contain the test pressure and obtain accurate results.
Question 3: What is the minimum test pressure typically required for a pressure integrity test on a residential gas piping system according to most North American codes?
- 1.5 psi
- 3 psi
- 10 psi (Correct answer)
- 25 psi
Correct answer: 10 psi
Most codes require a minimum of 10 psi (or 1.5 times the maximum allowable operating pressure, whichever is greater) for pressure integrity tests on residential systems.
Question 4: When performing a pressure drop test, a technician notices a pressure drop of 0.5 in. W.C. over 10 minutes. What does this indicate?
- The system is leak-free and passes the test
- A leak is present in the system (Correct answer)
- The gauge is malfunctioning
- Normal thermal expansion is occurring
Correct answer: A leak is present in the system
Any measurable pressure drop during a pressure drop test indicates a leak is present in the system, as a tight system should hold pressure.
Question 5: Which gas has the lowest explosive limit (LEL) making leak detection especially critical?
- Natural gas (methane)
- Propane (Correct answer)
- Butane
- All fuel gases have the same LEL
Correct answer: Propane
Propane has a lower LEL (2.1%) compared to natural gas (5%), meaning smaller concentrations of propane in air can create an explosive mixture.
Question 6: What is the primary reason soap solutions containing chlorides should NOT be used for leak detection on stainless steel gas piping?
- They are too thick to reveal small leaks
- Chlorides cause stress corrosion cracking in stainless steel (Correct answer)
- They leave residue that blocks gas flow
- They react with gas to form toxic compounds
Correct answer: Chlorides cause stress corrosion cracking in stainless steel
Chlorides in soap solutions cause stress corrosion cracking in stainless steel, compromising the pipe's structural integrity over time.
Question 7: After a gas leak is detected and repaired, what must a technician do before restoring gas service?
- Wait 24 hours for the repair to cure
- Re-test the repaired section to confirm the leak is eliminated (Correct answer)
- Notify the gas utility immediately
- Replace the entire section of pipe
Correct answer: Re-test the repaired section to confirm the leak is eliminated
Re-testing the repaired section confirms the repair was successful and the leak has been eliminated before restoring service.
G3 Leak Detection and Testing Procedures 1
Which leak detection method is most commonly used for a quick field check of gas piping joints?