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)|
|Plastic, PVC||0 – 0.0015|
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.