What does nominal pipe size refer to?

• A. A rough size designation for piping, not the exact outside diameter
• B. The exact outside diameter of the pipe
• C. The pipe's insulation thickness
• D. The color coding of the pipe system

Answer: (A)

Nominal pipe size is a rough size designation used to indicate the size category of a pipe without tying it to the exact outer diameter. This convention makes it easier to match pipes with fittings and components across different materials and wall thicknesses. The actual outside diameter varies with the pipe’s schedule (wall thickness) and material, so a nominal size doesn’t equal a precise measurement. For example, a 2-inch nominal pipe won’t have the same outside diameter across different materials or schedules. Insulation thickness and color coding are separate attributes, not used to define the pipe’s size, which is why they don’t describe nominal size.