Page 237 - Handbook of Materials Failure Analysis

5 Examples of Serious Failures of Water Supply and Wastewater 233

In 2003, a cracked cast iron pipe (400 mm in diameter) in a zone pumping station
was the cause of a water supply network failure in a town of 200,000 inhabitants.
In mid-2003, a town of 50,000 inhabitants suffered an incident of water contamina-
tion in the water supply network that lasted for 17 days. Coli group bacteria were
detected in the water supply pipeline in the amount of MPN¼99 (99 coli bacteria in
3
100 cm of water, while the admissible standard is 0). Due to information chaos, the
town succumbed to panic and inhabitants started to buy mineral water from shops.
The contamination was caused by improper operation of the water supply network.
The network was not rinsed properly after the application of phosphate preparations
used to facilitate removal of deposits from the network. During the crisis period, the
local hospitalrecorded 100cases of varioustypes ofailments relatedto thefailureevent.
Another failure event in 2003 affected a city of about 2 million inhabitants. An
arterial conduit of the water supply network suffered a breakdown in the vicinity of
the national stadium. Water flooded 1/4 of the stadium surface area. Many cars were
flooded. Moreover, about 25% of the inhabitants had no access to water.
In 2005, in a city of 550,000 inhabitants, a delivery collector sewer of 800 mm in
diameter (feeding sewage to one of the two sewage-treatment plants) was damaged
during drilling operations. As a result of this event, a part of the sewage had to go
without treatment, for a short period of time, over an overflow to the point of dis-
posal. The other part, in turn, was directed to a smaller sewage-treatment plant,
which resulted in facility overloading [13].
In 2007, a brick collector sewer with pear-shaped cross-section (1.20 1.50 m)
collapsed along a section of 50 m. It was the only point of disposal of sewage from
370,000 inhabitants. The failure resulted from improper selection of materials used
to construct the collector sewer (constructed in 1956).
A water supply network in a city of 700,000 inhabitants in central Poland, with a
water supply network length of about 1430 km, was analyzed in terms of suscepti-
bility to failure. The water supply network was made primarily of cast iron, steel,
PVC, PEHD, asbestos cement, and reinforced concrete. The analysis yielded the fol-
lowing damage types (Tables 9.7 and 9.8):

• Corrosion (also as a cause of damages)
• Transversal cracking
• Longitudinal cracking

Table 9.7 Failure Rate as a Function of Conduit Type
Type of Network Number of Failures Failure Rate One Failure on
Water Length in the Period (failure/km Pipe Length
Supply (km) 2008-12 year) (km)

Arterial 244 68 0.06 17.94
conduits
Distribution 1184 1853 0.31 3.19
conduits