Absolute roughness is a measure of the surface roughness of a material which a fluid may flow over. Absolute roughness is important when calculating pressure drop particularly in the turbulent flow regime. This article provides some typical absolute roughness values for common conduit materials.
The roughness of pipes, ducts and channels impacts on the flow rates and pressure losses for fluids passing through them. This roughness is generally expressed in units of length as the absolute roughness of the conduit material. For use in calculating the friction factor the absolute roughness is divided by the pipe diameter resulting in the relative roughness.
Absolute Roughness for Common Materials
This table contains typical values of absolute roughness for common construction materials.
|Drawn Tubing, Glass, Plastic||0.0015-0.01|
|Drawn Brass, Copper, Stainless Steel (New)||>0.0015-0.01|
|Flexible Rubber Tubing - Smooth||0.006-0.07|
|Flexible Rubber Tubing - Wire Reinforced||0.3-4|
|Wrought Iron (New)||0.045|
|Carbon Steel (New)||0.02-0.05|
|Carbon Steel (Slightly Corroded)||0.05-0.15|
|Carbon Steel (Moderately Corroded)||0.15-1|
|Carbon Steel (Badly Corroded)||1-3|
|Carbon Steel (Cement-lined)||1.5|
|Asphalted Cast Iron||0.1-1|
|Cast Iron (new)||0.25|
|Cast Iron (old, sandblasted)||1|
|Sheet Metal Ducts (with smooth joints)||0.02-0.1|
|Wood Stave, used||0.25-1|
|Concrete – Very Smooth||0.025-0.2|
|Concrete – Fine (Floated, Brushed)||0.2-0.8|
|Concrete – Rough, Form Marks||0.8-3|
|Water Mains with Tuberculations||1.2|
|Brickwork, Mature Foul Sewers||3|