1. On the Selection of the Type of
Pipes for Water Distribution
Networks
Boyan Borisov
UASEG - Sofia

2. The current situation
• Pipes are basic elements of Water Distribution
Networks /WDN/ and single pipelines
• Polyethylene /PE/ and ductile cast iron /DCI/– two
of the most widespread pipe materials for water
supply pipelines
• The current situation with the selection of pipe
material in practice

3. Outline of presentation
• 1. Short history and descriptions of compared
pipe materials
• 2. Description of the selection methodology and
quantitative and qualitative parameters
• 3. Analysis of some of the compared parameters
• 4. Discussion and conclusions

4. A short description of compared
materials
1. Ductile cast iron /DCI/
2. Polyethylene /PE/

5. Comparison methodology
Weight Rating for Valuation Rating for
Valuation for pipe
N Parameter coefficie pipe mat. for pipe pipe mat.
mat. j+1
nt j mat. J j+1
Parame Vi,j =
i Ki Rij Ri,j+1 Vi,j+1 = Ki.Ri,j+1
ter i Ki.Ri,j
i+ Parame Vi+1,j = Vi+1,j+1 =
1
Ki+1 Ri+1,j Ri+1,j+1
ter i+1 Ki+1.Ri+1,j Ki+1.Ri+1,j+1
Parame Vn,j =
n Kn Rn,j Rn,j+1 Vn,j+1 = Kn.Rn,j+1
ter n Kn.Rn,j

6. The quantitative parameters
1. Initial investment
min (Ci , j ; Ci , j 1 )
1. Purchase costs Ri , j
2. Construction costs Ci , j
2. Whole life costs Ci,j – the value of “initial
1. Initial investment investment” or “WLC” for
2. Operation and pipe type “j”
maintenance cost

7. The chosen comparison parameters:
qualitative ones
3. Environmental aspects
4. Corrosion resistance for DCIP
and slow crack growth
resistance for PE Rating “R” is
5. Impact resistance between 1 and 3
6. Thermal stability
Weight
7. Durability
coefficient is
8. Operational experience between 5 and
9. External load resistance 15%.
10. Resistance to water hammer

8. Parameter 1 - Initial investment
1. Price characteristics of both types of pipes
€/m’ Turning point
phenomenon
DCI
PE DN

9. Parameter 1 - Initial investment and
turning points of pipes and pipelines –
real data

10. Parameter 2 – Whole Life Cost
N
Ct
WLC t
t 1 (1 r /100)
• After initial investment the energy
consumption, i.e. head losses is decisive factor
• An analysis is made for the influence of pipe
roughness and the internal diameter

11. Influence of hydraulic roughness
Hydraulic roughness PE pipes DCIP
Pipes;
k1=0.01mm k1=0.03mm
“Individual concept”
Pipelines and networks;
k2=0.1mm k2=0.1mm
“Global concept”
• In transition zone friction factor “f” is slightly
influenced
• Difference in head losses for k=0.01 and k=0.3
is under 5 %

12. Influence of internal diameter
• Difference by 1 % in internal diameter causes
difference in head losses by 5 %
• There are bigger differences in internal
diameters of different pipe materials, incl. PE
and DCI

13. Two common WDN cases

14. The correct approach for choosing
diameter
Costs
WLC pipe mat. X1
WLC DX1
WLC pipe mat. X2
WLC DX2 Install. costs X1
Install. costs X2
WLC DX2 <WLC DX1
Operating
/Energy/ costs
Opt. DX1 Opt. DX2 Diameter

15. Environmental aspects
• Raw materials:
 for DCI pipes fresh iron ore or iron scrap
 for PE pipes: oil
• Carbon print
g of CO2 eq/1 m g of CO2 eq/1
Type g of CO2 eq/per
(DN 110 or DN m (DN 630 or
of pipe kg of pipe/year
100) /year DN 500) /year
PE 40.1 88.23 2819
DCI 20.7 246.33 1900
Note: The data is for the production and laying stage,
without transportation.

16. Durability for DCI and PE
• DCI pipes: the service life is so long that it is
even not mentioned in the product standard
• Thinner wall since 2010 and rubber gaskets
• PE pipes: the standard service life declared in
EU is 50 years; in some standards – 100 years
• There are now PE pipes which are 50 years old
and are in good condition

17. Summary - Qualitative parameters
Qualitative parameters DCI (K x R) PE (K x R)
3. Environmental aspects 5% x (2-3) 5% x (1-2)
4. Corrosion resist. for DCI 5% x (1-2) 5% x (2-3)
and slow crack growth for PE
5. Impact resistance 5% x (2) 5% x (1)
6. Thermal stability 5% x (3) 5% x (2)
7. Durability 10% x (2) 10% x (2)
8. Operational experience 5% x (1-3) 5% x (1-3)
9. External load resistance 5% x (2-3) 5% x (1-2)
10. Resist. to water hammer 5% x (2-3) 5% x (2)

18. Discussion
• In practice - tendency for exaggeration of some
disadvantages and advantages of the pipes;
• Standards, technical literature and own research
should be used instead manufacturer’s catalogues and
common opinions
• It has been confirmed that generally PE is appropriate
for smaller diameters and DCI for larger ones
• Consensus of stakeholders is needed for ratings of the
qualitative parameters and all weight coefficients

19. Conclusions
• Qualitative parameters still could be decisive
for the selection of pipe material
• The result of the comparison methodology
could vary in the course of time and for each
particular case
• The comparison methodology could be used
for all pipe materials

20. Next step
• The selection methodologies have to be
included in some form in the national design
legislation or gradually to be accepted as a
good practice