Page 295 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

DRINKING WATER AND SEWER SYSTEMS 273

concentration of metals, cation and anion concentrations, (iii) alkalinity, (iv) hard-
ness, (v) pH, and (vi) chlorine concentration.
Internal condition of pipes can be assessed through visual inspection photomi-
crographs, weight loss, pitting potential measurements, scale analysis, and corrosion
probe data. From the corrosion data, service life of the pipes can be estimated.
Metal release tests may be used to measure the corrosion rates and the accumula-
tion of corrosion products in water flowing through a plumbing system or distribution
network. It is desirable to use large loops to evaluate metal release rates to select the
suitable control strategy. The two systems in use are: (i) closed-loop system and (ii)
recirculation loop system. The pipe loop corrosion control system simulates closely
the consumer’s tap under different corrosion control strategies. When determining
the lead concentrations, the protocol for sampling the water is important. Stagnation
time, flushing, and the specific conditions of the installation under study influence
the results to a great extent.

4.18.7 Corrosion Control in Sewage Water Systems

Sewage water is pumped through sewer water piping to a treatment plant. The US
investment in sewage lines in the United States is nearly $1.8 trillion. Wastewater is
collected through relatively small diameter pipes and transmitted to treatment plants
through larger diameter pipes. Common materials of construction for sewage water
systems are concrete piping, steel, and ductile iron piping.
The mechanism of material degradation in sewer pipes is similar to potable water
systems. The internal corrosion may be more severe than in potable water because the
wastewater is not clean. The winterizing treatments of roads are a source of chloride,
which comes into contact with the pipe. Cement-based pipe experiences corrosion of
reinforced steel. The corrosion control method consists of using thicker pipe walls,
which provide for larger corrosion tolerance and a longer design life.
Table 4.34 represents a corrosion control program implementation flowchart for
internal corrosion.

4.18.8 Optimized Management by Combining Corrosion Control Methods
Increased wall thickness is one way of decreasing corrosion impact. The most com-
monly used repair methods for water systems with corrosion damage are given below.
The repair methods consist of addition of corrosion inhibitors, pH adjusters, alkalinity
controllers, hardness controllers to the water, application of CP, internal coatings and
linings, internal inspection, external coatings, monitoring with coupons, test stations,
and corrosion data loggers.
To prevent any further problems in the cases where lead and copper release is the
problem, it is advisable to consider the complete replacement of the tubes, fittings, fix-
tures and joints by corrosion-resistant components. The most commonly used repair
methods for water systems with corrosion damage are given in Table 4.35.