Which material is prohibited for use with metallic pipe and tubing?

The use of cast iron pipe fittings with metallic pipe and tubing is prohibited primarily due to concerns related to corrosion and compatibility. Cast iron is a brittle material that can crack or break under stress, which poses a risk in a pressurized environment like propane systems. Furthermore, when cast iron is used with other metals, such as steel or copper, it can create galvanic corrosion issues, leading to premature failure of the fittings and potentially hazardous leaks.

In contrast, plastic fittings, copper, and steel pipe fittings are generally considered safe and compatible for use with metallic pipes and tubing, as they either provide flexibility, resist corrosion, or maintain structural integrity under pressure. This ensures a safer and more reliable propane system.