Which type of piping is prohibited for underground gas distribution?

The prohibition of polypropylene and PVC piping for underground gas distribution stems from the material properties and safety standards necessary for handling gases such as natural gas or propane. These materials are not designed to withstand the pressures and potential chemical properties of gas environments.

Polypropylene and PVC are prone to degradation when exposed to certain elements found in underground environments, including moisture and soil chemistry, which can lead to failures or leaks over time. Furthermore, these plastics can become brittle under low temperatures and can soften or deform under higher temperatures, leading to a potential loss of integrity in gas distribution systems.

In contrast, galvanized steel, copper, and stainless steel have established properties that make them suitable for gas distribution and have been widely used in the industry. They possess excellent resistance to corrosion (in the case of galvanized and stainless steel), mechanical strength, and durability required for underground installations.