Plumbing Gas Piping Systems 1 — Questions and Answers
Question 1: What type of pipe is most commonly used for natural gas distribution inside residential buildings?
- PVC plastic pipe
- Black steel pipe (Correct answer)
- Copper tubing
- CPVC pipe
Correct answer: Black steel pipe
Black steel pipe is the most widely approved material for interior natural gas distribution due to its strength, durability, and resistance to permeation.
Question 2: Which gas has a specific gravity GREATER than air, causing it to sink and accumulate in low areas?
- Natural gas (methane)
- Hydrogen
- Propane (LP gas) (Correct answer)
- Carbon monoxide
Correct answer: Propane (LP gas)
Propane has a specific gravity of about 1.52 relative to air, so it sinks and can pool in basements, crawl spaces, and pits where it poses an explosion risk.
Question 3: What is the purpose of a drip leg (sediment trap) installed on a gas supply line near an appliance?
- To reduce gas pressure before the appliance
- To collect moisture and debris before they enter the appliance valve (Correct answer)
- To regulate gas flow rate
- To prevent gas from flowing backward
Correct answer: To collect moisture and debris before they enter the appliance valve
A drip leg collects condensate and pipe debris that would otherwise clog or damage the appliance gas valve and controls.
Question 4: What test method is required to verify gas piping integrity before placing the system in service?
- Smoke test using theatrical fog
- Pressure test with air or an inert gas (Correct answer)
- Hydrostatic (water) pressure test
- Vacuum test at negative pressure
Correct answer: Pressure test with air or an inert gas
Gas piping must be pressure tested with air or an inert gas (not the actual gas) to safely detect leaks before the system is charged.
Question 5: What fitting is typically installed at each gas appliance to allow individual shutoff without interrupting the entire system?
- Union fitting
- Tee fitting
- Appliance shutoff valve (gas cock) (Correct answer)
- Ball check valve
Correct answer: Appliance shutoff valve (gas cock)
An appliance shutoff valve (gas cock or stop valve) is required at each appliance connection to allow safe individual isolation for service or emergencies.
Question 6: What color jacket is standard on corrugated stainless steel tubing (CSST) used for gas piping?
- Black
- Red
- Yellow (Correct answer)
- Orange
Correct answer: Yellow
CSST gas piping is covered with a yellow plastic jacket, universally recognized as a gas-service identifier and providing physical protection.
Question 7: What is the minimum burial depth required for a natural gas service line running underground to a residential building?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 36 inches
Correct answer: 12 inches
Natural gas service lines must be buried at least 12 inches deep under normal conditions to protect them from surface disturbance and damage.
Plumbing Gas Piping Systems 1
What type of pipe is most commonly used for natural gas distribution inside residential buildings?