Mesman A0 Poster LESAM.indd
Transcription
Mesman A0 Poster LESAM.indd
Condition assessment of PVC water mains G.A.M. Mesman1,*, B. Schultz2 Introduction The Dutch drinking water network has a total length of about 116.000 km. More than 50% of this network is made of PVC pipes and the cohort has an average age of about 30 years, ranging from 60 to 0 years. The failure rate, as recorded systematically in a national database, shows to be low (0.025 failure/km/year). There is no clear time dependency in the failure pattern, which can be explained by earlier research results showing the material not to deteriorate under normal ground conditions. Failure is due to overloading of the pipe or insufficient initial quality. Three test methods are developed and tested to determine the (initial) quality of the PVC: the failure break surface inspection, the resistance of the material to DiChloroMethane at a specified Temperature (DCMT) test and the Resistance against Slow Crack Growth (RSCG). With these test methods failures can be analysed together with the loading pattern to determine the cause of failure and which subsequent action is best. A protocol for testing is developed that helps to determine the appropriate and most economical asset management strategy. 60 50 year 50 σY (MPa) Condition PVC main? 25 year 40 30 20 10 0 Yes 2 0 Figure 2. Result from DCMT test “Attacked”. 1 1 2 3 4 5 6 log t (sec) 3 7 8 9 10 y = -3.5475x + 43.691 Figure 1. Failed PVC drinking water main.. Failed pipe? No Yes Particles present? 4 Figure 4. Particles in the PVC matrix on the surface of the crack, probably crystaline PVC. Growth rings caused by slow crack growth can be seen around the particle. No DCMT = attacked Yes Figure 3. Result of a test for the resistance against slow crack growth, σγ below 12.5 MPa for 50 years. The 95% confidence interval lies between the dotted lines. No RSCG50y < 12.5 MPa Yes No Yes Failure rate high? No No Failure rate high? Yes Bad quality PVC. Replace main Replace pipe and monitor failure rate of main Failure rate (#/km/year) 0.07 0.06 0.05 Yes freq USTOREweb 0.04 0.03 0.02 0.01 0 1956- 1961- 1966- 1971- 1976- 1981- 1986- 1991- 1996- 2001- 20061960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 5 Years Wrong choice SDR. Replace main Figure 5. Averaged failure frequency of PVC water mains for the years 2009-2010 for the different years of construction. Figure 6. Scheme for condition assessment of PVC drinking water mains. Conclusions Condition assessment of PVC pipes will give an answer to the question which part of a failed main has to be replaced. For the condition assessment of PVC pipes three techniques have to be combined. These techniques are: • Visual inspection of the cracks of failed pipes on particles; • DCMT test on the investigated pipe; • Assessment of the resistance against slow crack growth. By using a protocol for ranking the techniques the total number of experiments can be limited. An answer to the question whether the whole main or just the failed pipe has to be replaced will follow from the protocol. 1. KWR Watercycle Research Institute, PO Box 1072, 3430 BB Nieuwegein, the Netherlands Watercycle Research Institute 2. OASEN, PO Box 122, 2800 AC Gouda, the Netherlands * Corresponding author: [email protected] This project was conducted within the Joint Research Program of the Dutch water companies 110802gm