The receiver pipe will be made from a less expensive material because of its large size. The rest of the oil loop will be made out of 1/2 inch thick M copper pipe. This pipe is very strong at high temperatures and can be easily fit together.
For the joints a high temperature solder or brazing will be used. Solder is easier to work with but has a lower melting temperature. Brazing requires an oxy-acetylene which can be expensive. The Oil plumbing will be heavy insulated. Fiberglas insulation can operate at high temperatures and is inexpensive but is difficult to work with.