Page 231 - Handbook of Materials Failure Analysis

3 Damage Analysis 227

• Temperature fluctuations
• Age
C: factors related to conduit operation:
• Maintenance, overhaul, and repair activities
• Operational procedures
• Network monitoring
• Identification and location of failures
• Failure removal

Anticorrosion protection that appeared among conduit protection factors refer primar-
ily to conduits and elements made of metal or concrete. In the case of water supply
conduits made of thermoplastics, one can observe the phenomenon of bacteria prolif-
eration on conduit walls. In the case of metal conduits, one observes surface corrosion
affecting considerable areas inside and outside a conduit, as well as local corrosion that
assumes various forms, such as corrosion pits, crevice corrosion, intergranular corro-
sion, etc. Both in water supply conduits and in wastewater disposal conduits, one
observes the phenomenon of microbially induced corrosion, which leads, among
others, to the formation of deposits inside conduits. The phenomenon of corrosion
in water supply and wastewater disposal conduits is correlated with numerous factors
that have an impact on conduit reliability. In the water supply network, these factors
include the quality of water transferred through a conduit, the type and humidity of the
soil and the quality of maintenance activities performed. In a wastewater disposal net-
work, they are related to phase interfaces between conduit material, air, and the flow-
ing liquid, to the aggressiveness of sewage, to the amount, quality and type of gases
generated in sewers as well as to the performance of pipeline operation activities. Cor-
rosion sources may already appear at the stage of conduit assembly if pipes were dam-
aged during transport, if conduit assembly works were not performed properly or if
anticorrosion insulation had been damaged or if connections are not made correctly.
When analyzing susceptibility of a conduit to failure in terms of its impact on
water quality, one should consider the corrosive impact of water on conduit material
and the impact of the material on water, as these processes are interconnected. As a
result, a corroded conduit is susceptible to damages, while such situation also
enhances secondary water contamination that manifests itself through the deteriora-
tion of organoleptic, physical, chemical, and microbiological properties of water
transferred through a conduit.
The standards prepared for the water supply and wastewater disposal sector
[20–22] assume that 25 years is the technical service life of conduits in a water supply
network (transit, arterial, and distribution conduits).
According to these standards, the criteria for selecting conduit service life should
take numerous factors into account, including:
– Application: aggressive sewage versus fresh water
– Materials of manufacture: resistance to corrosion
– Local conditions: soil humidity, soil and water conditions
– Monitoring of operating and technical conditions