Fuel transfer pipes
A non-metallic material, such as reinforced thermosetting resin tubing, is favored for the design of underground site piping due to its inherent corrosion resistance. Underground plumbing, consisting of a carrier pipe and a containment pipe, is almost always double-wall. For a leak detection system the interstitial space between the pipes is monitored.
Usually single-wall carbon steel is the fuel transfer pipes placed above ground inaccessible areas. Note that for aboveground applications even local authorities and insurance providers can need double-wall piping.