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Surface roughness of common materials : Overview, References

Pipe roughness for friction factor and pressure drop calculation

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Section summary
1. Surface roughness of common materials
2. Relative roughness

1. Surface roughness of common materials

What is the surface roughness of a steel pipe ? What is the surface roughness of concrete... ? The roughness is actually a measurement of all the asperities at the surface of a material, especially a pipe where it will oppose the flow of fluid.

Pipe roughness

The following table is summarizing usual pipe roughness for many materials used for piping or ducts.



Material Absolute Roughness
mm
Steel pipe - stretched 0.015
Steel pipe - commercial, laminated - NEW 0.05
Steel pipe - commercial, laminated - RUSTED 0.15-0.25
Steel pipe - welded NEW 0.03-0.1
Steel pipe - welded RUSTED 0.4
Iron pipe - galvanized 0.15-0.20
Cast iron - molded NEW 0.25
Cast iron - molded RUSTED 1-1.5
Glass, copper or brass stretched pipe 0.001
Concrete pipe - smoothed 0.3-0.8
Concrete pipe - coarse 3
Plastic pipe 0.002-0.007
Wood - ordinary 1-2.5
Stone (cut) 8-15

For steel pipes, when nothing more is precised, 0.05 mm is 1st good approximation.

2. Relative roughness

What is the relative roughness ? How to calculate the relative roughness ? The relative roughness is calculated by dividing the pipe roughness ε over the pipe diameter D

Relative Pipe Roughness = ε / D

In a more general expression, the diameter can be replaced by the hydraulic diameter.


What is the pipe roughness used for ? The pipe relative roughness is used to calculate the friction factor, and then the pressure drop for a fluid flow. What is the friction factors in pipes ? Have a look there : friction factor or Moody chart

Source
Mecanique et Rheologie des fluides en genie chimique, Midoux, Lavoisier Tec et Doc, page 277
Other internet sources