Which of the following is a measure of the smoothness of a pipe?

The smoothness of a pipe is primarily measured by the C value, often referred to as the "hazardous flow coefficient." This value is crucial in fluid mechanics, as it helps determine the friction loss that occurs when fluid flows through a pipe. A higher C value indicates a smoother pipe, which implies that there is less resistance to flow and a more efficient system.

In contrast, other options do not specifically measure smoothness. The pressure rating pertains to the maximum pressure a pipe can withstand, which is not related to flow smoothness. The flow coefficient is generally associated with the sizing of valves and fittings rather than the overall condition of the pipe itself. The diameter of the pipe is related to the volume of fluid it can carry but does not describe the internal surface texture. Therefore, identifying the C value as an indicator of smoothness provides a direct evaluation of how closely a pipe meets the ideal conditions for fluid flow.