Hazen-Williams Coefficient

Hazen-Williams coefficient, abbreviated as C, also called Hazen-Williams friction coefficient or, Hazen-Williams roughness coefficient, a dimensionless number, is used in the Hazen-Williams Equation.  The coefficient is used in fluid dynamics to calculate the resistance of water flow in a pipe network.  The lower the coefficient, the smoother the pipe is.  The higher the coefficient, the less fluid flow is restricted.  By using pipe materials with improved flow characteristics, energy costs for pumping can be reduced or smaller pipes can be used.

The Hazen-Williams coefficient represents the internal roughness of the pipe, taking into account factors such as pipe material, age, and condition.  It is used to incorporate the effect of pipe roughness on the flow characteristics.  The higher the coefficient, the smoother the pipe surface, resulting in a higher flow rate for a given pressure drop.  The Hazen-Williams coefficient varies depending on the pipe material, and it is typically determined through empirical testing.  The coefficient values for different pipe materials are usually available in engineering references and design manuals.

It's important to note that the Hazen-Williams equation is an empirical approximation and is most accurate for steady, uniform flow conditions in water supply systems.  For more complex or non-uniform flow situations, other equations, such as the Darcy-Weisbach equation, may be more appropriate.

Note that the Hazen-Williams Coefficient is '''not''' the same as the Darcy-Weibach-Colebrook friction factor, f.  These are not in any way related to each other.

 

Hazen-Williams coefficient formula
\(\large{ C = \frac {v}{ 1.318 \; r_h^{0.63}  \; m^{0.54} }  }\)     (mean flow velocity)
Symbol	English	Metric
\(\large{ C }\) = Hazen-Williams Coefficient, see below for values	\(\large{ dimensionless }\)
\(\large{ v }\) = mean flow velocity	\(\large{\frac{ft}{sec}}\)	\(\large{\frac{m}{s}}\)
\(\large{ r_h }\) = hydraulic radius	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ m }\) = hydraulic grade line slope	\(\large{ dimensionless }\)

 

Hazen-Williams coefficient formula
\(\large{ C = \frac {Q}{ 0.285 \; d^{2.63}  \; m^{0.54} }  }\)     (fluid flow rate)
Symbol	English	Metric
\(\large{ C }\) = Hazen-Williams Coefficient, see below for values	\(\large{ dimensionless }\)
\(\large{ Q }\) = flow rate	\(\large{\frac{ft^3}{sec}}\)	\(\large{\frac{m^3}{s}}\)
\(\large{ d }\) = pipe inside diameter	\(\large{ in }\)	\(\large{ mm }\)
\(\large{ m }\) = hydraulic grade line slope	\(\large{ dimensionless }\)

  

Hazen-Williams Coefficient
Material	Coefficient
Aluminum	130 - 150
Asbestos Cement	120 - 150
Asphalt-lined iron or steel	140
Brass	130
Cast Iron, cement lined	140
Cast Iron, coated	110 - 140
Cast Iron, new unlined	130
Cast Iron, old unlined	40 - 120
Cast Iron, uncoated	100 - 140
Cast Iron, 10 years old	107 - 113
Cast Iron, 20 years old	89 - 100
Cast Iron, 30 years old	75 - 90
Cast Iron, 40 years old	64 - 83
Cement lining	140
Concrete	100 - 140
Concrete, old	100 - 110
Copper	130 - 140
Corrugated Metal Pipe	60
Corrugated Steel	60
Deteriorated old pipes	60 - 80
Ductile Iron	120 - 145
Fiberglass	150
Galvanized Iron	100 - 120
Glass	130
Lead	130
Polyethylene	140
PVC, PE, GRP	120 - 150
Steel, new unlined	120
Steel, 15 years	200
Steel, riveted joints	95 - 110
Steel, welded joints	100 - 140
Steel, welded joints, lined	110 - 140
Steel, welded or steamless	100 - 120
Tin	130
Wood Stave	110