Buried Wet Return Line Material

RonA

I have to replace a 10 foot segment of an underground return line, part of a two-line system, in the basement of a 75 year old residence. It appears to have been replaced previously and is buried in concrete. The current return line is 1.5 inch I.P. Since there is predictable future corrosion, my question relates to protecting future generations from the scourge of buried pipe decomposition, realizing that nothing is perfect. There is no acceptable alternative path in this system. If iron pipe is the only consideration, then certainly that is what it shall be. However, other considerations include gray PVC (for hot water application) and copper (with appropriate dielectric unions.) The PVC would seem ideal due to its expected longevity but are there other issues? Effort is not a consideration; material issues transcend the installation issues.

If iron pipe is used, what is the absolute best medium in which to embed the pipe. Also, with regard to iron pipe, is galvanized pipe more appropriate than black pipe in the condensed water portion of the system? I will eventually replace the remainder of the near-floor grade return line.

Thanks for your analysis and comments.

[Deleted User]

We use

black steel or L copper. We don't use dialectrics in this application. We insulate all buried lines w/ sprayed foam insulation. Keeps the contaminated back fill from eating the pipe from the outside. Not sand. The heating & cooling of a buried uninsulated return can keep the pipe to ground interface damp much of the time. Dry & warm is good.

Big Ed

Cinders

When you bury the the return shovel in fresh soil and lime . Old basement soil if full of ash from when coil was burned. The cinders increases acidity.........