Plastic gas pipes are supposed to have an insulated wire running with them for the purpose of carrying a tracing tone and carrying electrolytic corrosion protection current to isolated metal sections.

Metal underground gas pipes are insulated from the soil so that the electric field for corrosion protection is concentrated at the surface of the pipe and to conserve on current. Metal underground gas pipes are protected from corrsion by connecting them to the negative side of a direct current power supply and the positive side of the supply to cargon anodes. This is why long distance gas line have periodic electrical junction boxes up on a post. This is also why a gas meter bar has a dielectric union - never ever bond around this dielectric union.

You could transmit broad band over the gas pipes and toner wires by superimposing a carrier current signal but the losses on the earth side of the insulation would be enormous and would have excessive noise from power line neutral current. You would only be able to get a few hundred bits per second out of the link.

Also, Dominion East Ohio Gas would object to this. They are very paranoid about gas safety because the War Materials Board during World War 2 made them build 2 liquified natural gas tanks out of substandard thickness of steel and insulation. Eventually, both tanks ruptured and burned down an entire neighborhood. If you want your gasfitting job to pass inspection, do not mention this incident to them - they are still sore about it.

Mike Cole, mc5w at earthlink dot net