Black pipe is strong, and a PITA to cut and thread. It will not take any kind of shifting or vibration. Copper is more forgiving and easy to work(cut and join) and more forgiving if shifted or vibrated. Copper comes in M(residential hard pipe), L(commercial hard pipe), and K(used by utility), there is a L soft as well. used often under ground to accommodate some shifting if need be. This might be helpful:
http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdfPage 21 through 29 will give the working pressure, burst pressure and includes the solder joint ratings as well.
