Absolute Roughness

Written by Jerry Ratzlaff on . Posted in Properties

Absolute roughness is a measure of the roughness of the inside of a flowing pipe. It is used in conjunction with the inside diameter to calculate the friction factor using a Moody Diagram, the Reynolds Number and the Darcy-Weisbach Equation

Abbreviated as \(\epsilon\) (Greek symbol epsilon)

Common values for the absolute roughness are listed below.

Type of PipeAbsolute Roughness in feetAbsolute Roughness in inches
Drawn tubing (glass, brass, plastic) 0.000005 0.00006
Commercial steel or wrought iron (new) 0.00015 0.0018
Commercial steel or wrought iron (existing) 0.0005 0.006
Cast iron (asphalt dipped) 0.0004 0.0048
Galvanized iron 0.0005 0.006
Cast iron (uncoated) 0.00085 0.0102
Wood stave 0.0006 to 0.0003 0.0072 to 0.0036
Concrete 0.001 to 0.01 0.012 to 0.12
Riveted steel 0.003 to 0.03 0.036 to 0.36