Black pipe is used for carrying natural or manufactured gas such as propane, water, oil, and steam. The pipe, which consists of non-galvanized steel, is widely available but more expensive to install.
Black pipe is a high-strength pipe that is coated with iron oxide, according to AllSteelPipe.com. It is commonly used for gas distribution to homes, to carry potable water or hot water from boilers, or to drain wastes. It is also used to transport oil by the oil industry.
Black pipe can be installed underground, which is not true of all piping. It is available in lengths that are pre-threaded. A hardware store will typically cut the pipe to order and thread it. Larger diameter black pipe is welded instead of threaded.
Black pipe can also be used to protect electrical wiring. It is harder to work with than many other types of pipe, and requires cast iron fittings and special tools, such as a tube cutter and a pipe vise.