Which type of fittings are permitted with steel pipe?

Malleable iron fittings are permitted for use with steel pipe due to their compatibility and physical properties. These fittings can withstand high pressures and provide a robust connection that is resistant to corrosion and mechanical stress. Malleable iron is designed specifically for heavy-duty applications, making it suitable for gas and fluid transport, which aligns with the requirements for joining steel pipe systems.

In contrast, aluminum and brass, while useful in other contexts, can have issues when paired with steel due to differences in expansion rates and electrolysis, which can lead to corrosion over time. PVC fittings are not suitable for steel pipe because they are designed for a different application and do not have the same mechanical strength or heat resistance required for high-pressure gas systems. Thus, malleable iron is the correct choice for ensuring safe and effective connections in steel pipe installations.