How is the wall thickness of steel pipe designated?

The wall thickness of a steel pipe is designated by the schedule number. This system categorizes pipes based on their wall thickness relative to their nominal diameter. The schedule number corresponds to specific wall thicknesses, with lower schedule numbers indicating thinner walls and higher schedule numbers indicating thicker walls. This standardized designation allows for easier identification and selection of pipes for various applications, ensuring that the appropriate pipe can be chosen based on pressure requirements and other factors.

The other options provided do not serve as designators for wall thickness in steel piping. The CRN number relates to the certification of pressure vessels in Canada, diameter merely refers to the external measurement of the pipe, and material strength number typically refers to the tensile strength of the material rather than its dimensions.