Establishment of Leakage Accident Rate Curves for Drinking Water Pipes

Transcription

1 Establishment of Leakage Accident Rate Curves for Drinking Water Pipes H. Matsushita (Japan Water Research Center) Y. Takahashi Y. Suzuki (Japan Water Research Center) H. Taniguchi A. Koizumi (Tokyo Metropolitan University) 1

2 Introduction 1 In the thirty years between 1950 and 1980, the coverage rate of water supply systems in Japan increased threefold. Currently, 97.5% of all the people in Japan are served by water supply systems. Along with the increase in the coverage rate, various types of pipes have been used in water supply systems. Asbestos cement pipes : ACP Gray cast iron pipes : CIP Polyvinyl chloride pipes : PVC Steel pipes : SP Ductile cast iron pipes : DIP As Japan is an earthquake-prone country, use of earthquake-proof pipes has increased in recent years. 2

3 Introduction 2 The statutory life span of pipelines in Japan is 40 years. This is designated by law as the period of depreciation for pipelines. Although the period does not indicate actual useful life, it is considered to be one standard for estimating pipeline life spans in Japan. Soil and groundwater around pipes in Japan are slightly acidic, and depending on soil and installation conditions, pipes sometimes deteriorate rapidly due to corrosion. 3

4 Introduction 3 We studied leakage accident rate curves based on the relationship between the leakage accident rate and operating period for different pipe types and materials. Thus, we are developing a method to estimate the deterioration rate of pipelines. This study is a part of an ongoing e-pipe research project conducted by the Japan Water Research Center. Participants : Universities, Drinking water utilities, and Private companies Research Period : Fiscal year

5 Study method Leakage accident data in this study Research Project e-pipe New Epoch Total Surveyed years (Fiscal year) 2006, , 2005 Number of surveyed utilities Number of responding utilities Response rate 63.3% 62.2% Total leakage accidents 10,144 12,286 22,430 Accident data with details 4,317 2,136 6,453 Details : pipe age and pipe material, etc. 5

6 Leakage accident data in this study Age of pipe Pipe Type (years) CIP SP ACP PVC DIP Total , , , Total , ,643 Note : CIP = gray cast-iron pipes SP = steel pipes ACP = asbestos cement pipes PVC = polyvinyl chloride pipes DIP = ductile cast-iron pipes 6

7 Relationship between pipe age and leakage accidents Leakage accidents (number) ACP = asbestos cement pipes CIP = gray cast-iron pipes PVC = polyvinyl chloride pipes SP = steel pipes DIP = ductile cast-iron pipes DIP PVC SP Age of pipe (years) CIP ACP 7

8 Pipe length data Pipeline length by age Age of pipe Pipe Type (km) (years) CIP SP ACP PVC DIP Total , , ,809 1, ,912 8, ,265 1, ,127 10,951 22, ,661 1, ,050 20,467 31, ,498 1,177 6,988 23,908 34, ,659 8,417 30,051 41, ,539 8,089 35,399 45, ,301 9,591 46,774 60, ,224 9,344 43,312 53, ,081 37,906 46,911 Total 16,071 15,331 1,979 58, , ,474 Note: Based mainly on data from Statistics on water supply (Japan Water Works Association) 8

9 Existing pipeline length by year 350,000 Existing pipeline length (km) 300, , , , ,000 ACP = asbestos cement pipes CIP = gray cast-iron pipes PVC = polyvinyl chloride pipes SP = steel pipes DIP = ductile cast-iron pipes ACP DIP PVC CIP 50,000 SP Fiscal year 9

10 Removed pipeline length by year Removed pipe length (km) 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1, ACP = asbestos cement pipes CIP = gray cast-iron pipes PVC = polyvinyl chloride pipes SP = steel pipes DIP = ductile cast-iron pipes CIP PVC ACP DIP SP Fiscal year 10

11 Leakage accident rate with detailed data: Ad We should calculate leakage accident rates using data on all 22,430 leakage accident cases, but many utilities do not know the pipe type or years of installation of all their pipelines, and details of leakage accidents have not always been recorded. So, we first calculate the leakage accident rate with data from accidents for which details are known as follows: Ad = Nd Ly Ad: Rate of leakage accidents with known details by pipe age (number/km) Nd: Number of leakage accidents with details by pipe type and age Ly: Pipeline length by type and age (km) 11

12 General leakage accident rate: Ag Then we assumed that the characteristics of the accident data with details can represent all the accident data. This assumption allowed us to calculate the general leakage accident rate as follows: Na Ag = Ad Nd Ag: General leakage accident rate by pipe age (number/km) Na: Number of all leakage accidents by pipe age Nd: Number of leakage accidents with known details for each pipe type and age Ag is basic rate for each pipe material, which leads corrected rate for practical use. 12

13 Results of calculated general leakage accident rate Age of pipe (years) General leakage accident rate (number/km) Representative age of pipe Pipe Type CIP SP ACP PVC DIP

14 General leakage accident rate curves Ag Leakage accidental rates (number/km/year) ACP = asbestos cement pipes CIP = gray cast-iron pipes PVC = polyvinyl chloride pipes SP = steel pipes DIP = ductile cast-iron pipes Age of pipe (years) PVC SP ACP CIP DIP 14

15 Correction coefficients (1) Factors affecting leakage accident rate Factor CIP SP PVC DIP Ground condition (hard/soft) Pipe diameter Effect of polyethylene encasements for iron pipe Joint types (screw coupling or welding) Joint types (TS: tapered adhesion socket joint RR: rubber ring socket joint) Corrected leakage accident rate Ac = Ag C g C d C e C j Ac: Corrected leakage accident rate (number/km) Ag: General leakage accident rate (number/km) Cg, Cd, Ce, Cj: Correction coefficients 15

16 Correction coefficients (2) Joint type Ground condition Pipe diameter (mm) Examples of correction coefficients (for PVC) TS (tapered adhesion socket) RR (rubber ring socket) hard soft hard soft This table shows correction coefficients for PVC pipes as an example. The number in italics is a benchmark value 1.0 for numerical comparison. 16

17 Conclusion In this research, we created general leakage accident rate curves for every type of pipe, including resin pipes and iron pipes. In addition, we are currently establishing correction factors taking variations in pipe diameter, soil conditions, joint types and the effect of polyethylene encasement into account. Drinking water utilities will be able to easily explain to their customers the necessity for replacing pipelines, showing them the increased frequency of leakage accidents that occur as pipelines age or expenditures caused by accidents, which can both be calculated from leakage accident rates. Thus, water utilities can promote the replacement of aging, deteriorated pipes, ensuring that sustainable pipelines remain in place for the next generation. 17

18 Thank you for your attention 18

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21 Leakage accidents (number) Age of pipes and leakage accidents Pipes have been removed Age of pipe (years) 21

22 Length of asbestos cement pipe by year Existing Removed 22