Which type of piping material is NOT suitable for underground installation?

Wrought iron is not suitable for underground installation primarily due to its susceptibility to corrosion when exposed to moisture and soil conditions. Unlike materials specifically designed for underground use, such as uPVC, which is resistant to corrosion and chemical degradation, wrought iron lacks protective coatings that prevent rust. Over time, the corrosion can lead to structural failures and leaks, making it unreliable for transporting fluids or gases underground.

In contrast, the other materials listed, such as uPVC, stainless steel, and galvanized iron, possess properties that make them more suitable for underground applications. uPVC is lightweight and resistant to a variety of chemicals, making it an excellent choice for long-term underground installations. Stainless steel, while more expensive, offers high strength and excellent resistance to corrosion in a variety of environments. Galvanized iron is coated with a layer of zinc that provides some protection against corrosion, though it may still be less ideal compared to the other options. Therefore, the material choice for underground piping must prioritize durability and resistance to environmental factors, which is why wrought iron is not a suitable option.