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3-2_3. presentation 8


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3-2_3. presentation 8

  1. 1. On the Selection of the Type of Pipes for Water Distribution Networks Boyan Borisov UASEG - Sofia
  2. 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. 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. 4. A short description of compared materials1. Ductile cast iron /DCI/2. Polyethylene /PE/
  5. 5. Comparison methodology Weight Rating for Valuation Rating for Valuation for pipeN 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,ji+ 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. 6. The quantitative parameters1. Initial investment min (Ci , j ; Ci , j 1 ) 1. Purchase costs Ri , j 2. Construction costs Ci , j2. 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. 7. The chosen comparison parameters: qualitative ones3. Environmental aspects4. Corrosion resistance for DCIP and slow crack growth resistance for PE Rating “R” is5. Impact resistance between 1 and 36. Thermal stability Weight7. Durability coefficient is8. Operational experience between 5 and9. External load resistance 15%.10. Resistance to water hammer
  8. 8. Parameter 1 - Initial investment1. Price characteristics of both types of pipes €/m’ Turning point phenomenon DCI PE DN
  9. 9. Parameter 1 - Initial investment andturning points of pipes and pipelines – real data
  10. 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. 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. 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. 13. Two common WDN cases
  14. 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 X2WLC DX2 <WLC DX1 Operating /Energy/ costs Opt. DX1 Opt. DX2 Diameter
  15. 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 orof pipe kg of pipe/year 100) /year DN 500) /year PE 40.1 88.23 2819 DCI 20.7 246.33 1900Note: The data is for the production and laying stage,without transportation.
  16. 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. 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 PE5. 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. 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. 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. 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