GPT Gas Pipe Installation & Repair 3 — Questions and Answers
Question 1: What test is required to verify the integrity of a gas piping system before it is placed into service?
- Hydrostatic pressure test with water
- Pressure test using air, CO2, or nitrogen at required test pressure (Correct answer)
- Visual inspection only
- Flow test with gas at operating pressure
Correct answer: Pressure test using air, CO2, or nitrogen at required test pressure
Gas piping must be pressure-tested with an inert gas (air, nitrogen, or CO2) before being placed into service to detect leaks without using combustible gas.
Question 2: According to NFPA 54, what is the typical test pressure for gas piping systems operating at 0.5 psig or less?
- 1 psig for 10 minutes (Correct answer)
- 3 psig for 10 minutes
- 1.5 times operating pressure for 24 hours
- 10 psig for 15 minutes
Correct answer: 1 psig for 10 minutes
For systems operating at ½ psig or less, NFPA 54 requires a test pressure of at least 3 inches w.c. (≈0.1 psig), but many jurisdictions require at least 1½ times the working pressure, commonly 1 psig.
Question 3: Which fitting is NOT allowed in a concealed gas piping installation inside walls?
- Welded joints
- Brazed fittings
- Mechanical (compression) couplings (Correct answer)
- Press-fit fittings listed for gas
Correct answer: Mechanical (compression) couplings
Standard mechanical or compression couplings are generally not permitted in concealed locations because they require periodic inspection and adjustment.
Question 4: What is the minimum clearance required between a gas meter and an electrical meter or panel?
- 3 feet (Correct answer)
- 5 feet
- 10 feet
- No clearance required if separated by a wall
Correct answer: 3 feet
Gas meters must maintain at least 3 feet of separation from electric meters, service panels, and other ignition sources per code.
Question 5: When sizing a gas pipe, which factor has the GREATEST effect on pressure drop across the run?
- Pipe color
- Pipe length (Correct answer)
- Type of gas (natural vs. propane)
- Pipe wall thickness
Correct answer: Pipe length
Pressure drop increases with pipe length; longer runs require larger diameter pipe to maintain adequate pressure at the appliance.
Question 6: A yellow odorant (mercaptan) is added to natural gas primarily to:
- Improve combustion efficiency
- Enable leak detection by smell (Correct answer)
- Prevent corrosion inside steel pipes
- Stabilize pressure in distribution mains
Correct answer: Enable leak detection by smell
Mercaptan gives natural gas its rotten-egg odor so leaks can be detected by smell, since natural gas is otherwise colorless and odorless.
Question 7: Where should a manual shutoff valve be located relative to each gas appliance?
- At the gas meter only
- Within 6 feet upstream of the appliance in an accessible location (Correct answer)
- Downstream of the appliance flex connector
- Only at the main service entry
Correct answer: Within 6 feet upstream of the appliance in an accessible location
Code requires an accessible manual shutoff valve within 6 feet of each appliance, upstream of any flexible connector, so the appliance can be isolated quickly.
GPT Gas Pipe Installation & Repair 3
What test is required to verify the integrity of a gas piping system before it is placed into service?