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Absolute Pipe Roughness

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'Absolute Pipe Roughness' (ε) is a measure of pipe wall irregularities of commercial pipes. Other than pipes, absolute roughness is also used for representing the irregularities of other equipment walls, for example, walls of heat exchanger shell. The absolute roughness has dimensions of length and is usually expressed in millimeter (mm) or feet (ft).

'Relative Roughness' or 'Roughness factor' of a pipe wall can be defined as the ratio of absolute roughness to the pipe nominal diameter. Relative roughness factor is often used for pressure drop calculations for pipes and other equipments. The relative roughness factor is an important parameter for determining friction factor based on Reynold's number for flow in a pipe.

Relative roughness = ε/D

Absolute Roughness is usually defined for a material and can be measured experimentally.

Following table gives typical roughness values in millimeters for commonly used piping materials.

Surface Material Absolute Roughness Coefficient - ε in mm
Aluminum, Lead 0.001 - 0.002
Drawn Brass, Drawn Copper 0.0015
Aluminum, Lead 0.001 - 0.002
PVC, Plastic Pipes 0.0015
Fiberglass 0.005
Stainless steel 0.015
Steel commercial pipe 0.045 - 0.09
Stretched steel 0.015
Weld steel 0.045
Galvanized steel 0.15
Rusted steel 0.15 - 4
Riveted steel 0.9 - 9
New cast iron 0.25 - 0.8
Worn cast iron 0.8 - 1.5
Corroding cast iron 1.5 - 2.5
Asphalted cast iron 0.012
Galvanized iron 0.015
Smoothed cement 0.3
Ordinary concrete 0.3 - 3
Well planed wood 0.18 - 0.9
Ordinary wood 5