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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

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.

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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