Black tube is a type of common steel pipe.

Cold rolled steel that is heated to the annealing temperature becomes black on the surface due to high-temperature contact with air, and it is called black annealed steel. Since its surface has not been brightened, it remains black. The physical properties become softer, making it easier to weld and form into steel pipes. The common hardness is 57HRB, and it can be annealed to different hardness levels as needed.