Which type of pipe fittings should NOT be used for metallic pip and tubing?

Cast iron pipe fittings should not be used for metallic pipe and tubing due to several reasons related to compatibility and structural integrity. Cast iron has a brittleness that can make it less suitable for applications involving metallic piping systems, especially those that may experience vibrations, shifts, or thermal expansion.

In addition, the properties of cast iron can lead to issues with corrosion and potential leaks when used in conjunction with different metals. This is particularly important in systems designed to transport propane or other gases, where maintaining a secure and leak-free environment is critical for safety and efficiency.

In contrast, brass, steel, and aluminum fittings are commonly utilized in metallic piping systems due to their durability, strength, and corrosion resistance, making them more appropriate choices for these applications.