Page 222 - Handbook of Materials Failure Analysis

218 CHAPTER 9 Reliability and failure analysis of wastewater systems

– Resistance to corrosion and aggressive compound action
– Durable
– Resistant to temperature changes, both of the external environment and of the
transferred medium
– Resistant to shape deformation
– Resistant to abrasion
– Ease of manufacture and assembly
– Homogenous molecular structure
– Inexpensive to manufacture, implement, and operate
– Readily available on the market

The above requirements concerning the quality of materials to be used may be
extended to cover additional features that are related to specific local conditions.
In the context of a broad assortment of products and materials considered, particular
significance should be ascribed to the problem of how to select a material that is best
fitted to a planned investment in network infrastructure. Water supply and wastewa-
ter disposal infrastructure is found in every public location, urban agglomeration,
rural housing area, building, facility, industrial sector, or branch of industry. At
the same time, water supply systems and wastewater disposal systems play a very
important role in terms of reliability of water supply and wastewater disposal. As
they belong to complex network systems, they simultaneously fulfill several func-
tions within a given area. Large-scale systems have been functioning in an organized
manner for over 140 years in various countries. Vulnerability of such systems to fail-
ure has been investigated in Poland for over 50 years [3–9].
Investigations cover analyses of types and causes of damages, as well as identi-
fication of various reliability parameters. The range of investigated objects is highly
differentiated and covers, for instance, conduits of municipal and rural water supply
networks; transit, arterial, distribution conduits; household connection lines; con-
duits operating in various soil conditions (e.g., in zones affected by mining damages
or increased risk of seismic activity); conduits made of a variety of materials. In the
case of wastewater disposal networks, the investigations cover collector pipes, net-
work conduits, house drains, transfer conduits or small-sized, local wastewater dis-
posal systems. The research also covered network systems located in a variety of
industrial facilities, both in small-sized plants and in large-scale factories.
About 50% of the length of the water supply networks in Poland is still made of
traditional materials, yet water supply and wastewater disposal conduits are no lon-
ger made of steel, while gray cast iron is replaced mainly by nodular cast iron or
plastics.
Figure 9.1 presents changes that occurred between 1992 and 2005 in the distri-
bution of percentage shares of particular materials in the examined water supply
networks.
It should be underscored that small diameter conduits (primarily DN 100 and DN
150) constitute a clear majority of water supply networks. In big cities, conduits that
are 100 and 150 in diameter cover about 50% of the length of municipal networks.