Surface roughness of common materials

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

Material Roughness
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

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

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.

Mecanique et Rheologie des fluides en genie chimique, Midoux, Lavoisier Tec et Doc, page 277
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