Page 236 - Handbook of Materials Failure Analysis

232 CHAPTER 9 Reliability and failure analysis of wastewater systems

Table 9.6 Generalized Values of the Failure Rates of Water Supply Conduits
as a Function of Conduit Material, Based on Data Collected in 2008 (According
to Kwietniewski and Rak [14])
Failure Rate (failure/km year)
Material Water Supply
Gray cast iron 0.47
Nodular cast iron 0.08
Steel 0.83
PVC 0.09
PE 0.08
Concrete 0.29

5 EXAMPLES OF SERIOUS FAILURES OF WATER SUPPLY
AND WASTEWATER DISPOSAL SYSTEMS: CASE STUDY
The factors most often leading to failure of utility network systems include: lack of
employment of protection methods, lack of protective devices, lack of preventive
measures, or faulty operation resulting from operational errors [6,19,30]. Serious
failures occur frequently; for instance, the last one that occurred on 30th July
2014 at the University of California, Los Angeles, where a 90-year-old water supply
conduit cracked at the fringe of UCLA and flooded streets, garages, and sports
halls. The period between 2000 and 2010 witnessed 13 spectacular system break-
downs in Polish cities that resulted in the paralysis of almost entire district and led
as a consequence to disruptions in the functioning of entire cities that lasted for
some time. The breakdowns were related both to failures of water supply networks
and to defectiveness of wastewater disposal networks. They were often related to
susceptibility to failure that resulted from faulty operation of networks, mechanical
damages, errors in network operation, unpredictable and extreme atmospheric con-
ditions (impact of torrential rains on wastewater disposal networks or of severe
draughts on water supply networks), as well as from aging of materials, etc.
Research conducted in this domain provides a broad perspective on the relations
between materials used, types of failures, and reliability analyses, as well as many
other factors that influence the functioning of both water supply and wastewater
disposal networks.
One of the major large-scale failures occurred in 2002, when 70,000 town inhab-
itants were deprived access to potable water for about 24 h. The failure was caused
by a cracked conduit with a diameter of 1200 mm that supplied water to rapid-flow
filters at the water purification plant. The press was informed about this failure event.
This allowed the authorities to avoid panic among water consumers. The effects of
this situation could have been minimized if a water reserve in tanks had been avail-
able during the failure period [14,31].