In fluid mechanics, tubing roughness is the unevenness of the inside wall of a pipe, which affects the flow of fluids through the pipe (it has significant impact of losses due to friction). The roughness of a pipe is a function of the material it's made from, how it was manufactured, and its environment. Although manufacturers specify values upon sale of pipe or tubing, but these values can change with time due to buildup of scale and other material. See also autoRTA: Wellbore Model .
The typical absolute roughness used for new well tubing calculations is often quoted as 0.0006 in, while older well tubing can easily have an absolute roughness of 0.009 in. In producing wells, it is difficult to tubing roughness measure accurately without recorders at the inlet and outlet of the flow path. Plus roughness can vary substantially along the flow path (whether vertical or horizontal).