Plumbing Gas Piping Systems

Question 1

What type of pipe is most commonly used for natural gas distribution inside residential buildings?

Accepted Answer

Black steel pipe

Answer

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?

Accepted Answer

Propane (LP gas)

Answer

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?

Accepted Answer

To collect moisture and debris before they enter the appliance valve

Answer

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?

Accepted Answer

Pressure test with air or an inert gas

Answer

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?

Accepted Answer

Appliance shutoff valve (gas cock)

Answer

An appliance shutoff valve (gas cock or stop valve) is required at each appliance connection to allow safe individual isolation for service or emergencies.

Plumbing Practice Test

Plumbing Practice Test

Plumbing Gas Piping Systems