Which type of pipe is not permitted for gas piping?

Cast iron is not permitted for gas piping primarily due to its inherent properties and the potential risks associated with its use in gas applications. Cast iron is known for being brittle and can easily crack or break under stress or impact. This brittleness can lead to leaks in gas systems, which pose significant safety hazards such as explosions or fires.

In contrast, materials like steel, plastic (specifically certain grades designed for gas), and aluminum are typically allowed in gas piping systems because they offer better flexibility, durability, and resistance to corrosion when used appropriately. Steel, for instance, is commonly used for its strength and ability to withstand pressure, while specific types of plastic are designed to handle the characteristics of gas safely.

Understanding the materials appropriate for gas piping is crucial for both safety and compliance with building codes and regulations, which often specify the types of materials that can be used in gas installations to ensure reliable and safe operation.