According to NFPA 54, which piping material is prohibited for use with natural gas?

The prohibition of cast iron piping for use with natural gas, as specified by NFPA 54, arises from concerns about the potential for brittleness and failures, especially in applications involving gas. Cast iron can become brittle over time due to corrosion or stress, which can lead to dangerous leaks. In systems designed to transport natural gas, integrity and the ability to withstand pressure fluctuations and environmental conditions are crucial for safety.

Other materials, such as steel and copper, are permitted under NFPA 54 because they have stronger mechanical properties and better long-term performance in gas applications. Steel, for instance, is commonly used because it can handle high pressure and is resistant to burst under most conditions expected in natural gas piping. Copper is also well-regarded due to its durability and resistance to corrosion in certain environments. Plastic, while allowed in some applications, is typically used in specific contexts and must meet certain standards to ensure safety and reliability.

Thus, the prohibition of cast iron is a safety measure aimed at preventing leaks and catastrophic failures in natural gas piping systems.