The pressure rating of schedule 40 black, or carbon steel pipe, varies with the inner and outer diameters of the pipe, ranging in value from 188 to 696 pounds per square inch gauge. This range encompasses pipe outside diameters from 1/2 inch to 20 inches.
The steel pipe size with the highest pressure rating has an outside diameter of 6.625 inches, an inside diameter of 6.065 inches and a wall thickness of 0.280 inches. The thickness of this pipe requires electric resistance welding, commonly used for larger pipe, while smaller pipe uses a different continuous welding process.
The schedule of a pipe is equal to the ratio of the service pressure rating divided by the allowable stress rating, multiplied by 1,000. There are 14 different schedules of pipe, and the higher the schedule number, the thicker the pipe is.