Pipe Sizing Calculation – Part 5: Determining the Relative Roughness Using Table

This article will show the table for absolute roughness (different to coefficient of friction) of pipe surfaces of few commonly used materials. The absolute roughness is used in the relative roughness calculation and in the water piping system sizing design calculations through Darcy–Weisbach equation.

 

Absolute Roughness Value table for Different Pipe Materials:

Pipe surface materials Absolute roughness value ( k in mm)
Aluminum 0.0012
Brass 0.001
Cast iron 0.26
Copper 0.0015
Concrete 0.3-3
Cement 0.3
Drawn tube 0.0015
Galvanized iron 0.15
Plastic, PVC 0 – 0.0015
Steel 0.045

 

The water pipe sizing calculation example, we are dealing with, has galvanized iron (GI) tubes. From the above absolute surface roughness table we can see the value for GI pipe is 0.15.

 

Relative roughness is the ratio of the absolute roughness and hydraulic diameter.

 

For our home water tube sizing example,

The value of relative roughness  =absolute roughness / hydraulic diameter (refer part-4)

= 0.15/ 20 = 0.0075

In the next part (part-6), we will calculate the Reynolds number for the piping system.

 

 

Aluminum

0.0012

Brass

0.001

Cast iron

0.26

Copper

0.0015

Concrete

0.3-3

Cement

0.3

Drawn tube

0.0015

Galvanized iron

0.15

Plastic, PVC

0 – 0.0015

Steel

0.045

Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies.
Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

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