Black steel pipe, or iron pipe, is made of steel that has not been coated with a substrate such as zinc or paint. Since it has a dark-colored surface that is formed by iron oxide during the manufacturing process, it is called black steel pipe. When burying black steel pipe, the pipe is coated with a plastic (usually green) for underground use.
In residential work, black steel pipe is very labor-intensive to install, since each length of pipe is connected by a threaded coupling. When turning a corner, a threaded 90-degree fitting is used. Special lengths have to be cut and then threaded. The time to make these connections is considerable. For that reason, we use plastic whenever possible.
