Which of the following materials is NOT approved for gas piping?

Cast iron is not an approved material for gas piping in most modern plumbing codes due to its susceptibility to corrosion and its inability to withstand the stresses of gas service. Gas piping systems require materials that can handle the pressures and conditions of transporting gaseous fuels without leaking or breaking down over time.

Steel, polyethylene, and copper are considered suitable materials for gas piping. Steel is durable and can be welded, making it strong for carrying gas. Polyethylene is flexible and resistant to corrosion, which makes it advantageous for underground installations where it won’t be exposed to moisture and other environmental factors. Copper is also recognized for its durability and resistance to corrosion, while being relatively easy to install.

The use of cast iron in gas piping has largely been phased out in favor of these more reliable materials, highlighting the importance of selecting materials that meet current safety and performance standards in gas systems.