Sheet Metal Journeyman Practice Test

Gas piping must use a metal that can handle internal gas pressure, resist movement and vibration, and form reliable, leak-tight joints. Cast iron is not suitable because it is brittle and prone to cracking or breaking under impact or movement. Its joints are difficult to seal properly for gas, which can lead to dangerous leaks. That’s why cast iron piping is not used for gas service. The other metals listed—copper, steel, and, in some cases, aluminum—are used in gas piping because they can be joined reliably and maintain a tight, safe line.