Black steel pipe is steel that is not galvanized with a protective coat of zinc. Its dark color results from the iron oxide that covers it, and it is sometimes referred to as black iron piping.
In gas transport, black pipe is very durable, but it corrodes easily. It is used for low-pressure, low-heat water pipes that otherwise quickly corrode. Black iron pipe is coarse to the touch, scratches easily and flakes. Black iron pipe tends to leak at the connector spots and is time-intensive to repair. Black iron pipe is less expensive than steel, but it is not as energy efficient. However, it is more readily available, which makes its use convenient.