Page 288 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

266 CORROSION CONTROL AND PREVENTION

TABLE 4.28 The Most commonly Used Corrosion Control Methods for Water
Systems
Components in Water System Corrosion Control Method
Steel drums Increased wall thickness
General water infrastructure pH adjusters, corrosion inhibitors, alkalinity controllers,
hardness controllers
Storage tanks Cathodic protection (CP); internal coatings; external
paint coatings
Ductile iron, cast iron, and steel Internal linings, internal inspection
pipes-internal corrosion
Cement-based pipe Internal lining-cement mortar; cathodic protection (CP)
Ductile iron, cast iron, and steel External coatings
pipes
External corrosion Corrosion coupons, test stations, corrosion data loggers
Lead pipe Replacement with copper pipe
Copper pipe Prevention by improved tube production
Nonferrous alloys – Fittings, Replacement with corrosion-resistant components
fixtures, joints
Sewage pipes Increased wall thickness

hydrogen sulfide, methane, radon, iron, manganese, and VOC aeration is effective
for the removal of carbon dioxide. Carbon dioxide in turn directly affects pH and dis-
solved inorganic carbon, the two parameters that significantly influence the solubility
of lead and copper. Under the right water quality conditions, aeration can serve as a
potential corrosion control treatment by removing CO and subsequently increasing
2
pH and decreasing dissolved inorganic carbon. The degree to which aeration affects
corrosion depends on such raw water quality parameters as pH, dissolved inorganic
carbon dissolved oxygen, as well as the efficiency of removal of CO (43).
2
Chemicals used to treat raw water and improve its quality include corrosion
inhibitors, pH adjusters and alkalinity, and hardness-controlling agents. The
commonly used water treatment chemicals are soda ash, sodium bicarbonate,
sodium hydroxide (caustic soda) plus carbon dioxide, lime, alkaline media filters,
combinations such as limestone slurry, carbon dioxide, sodium hydroxide. All US
water utilities are required to always monitor the water quality by an analysis of
treated water. The samples for analysis are taken at regular time intervals and at
different locations spread out over the system.

4.18.3 Corrosion Inhibitors, pH Control, and Alkalinity Adjusters
In addition to water quality control as per the Safe Drinking Water Act (SDWA),
the application of chemicals for adjusting pH is one of the main options of internal
corrosion control. It should be noted that pH control alone is not sufficient to counter
corrosion problems. In such cases, corrosion inhibitors may be used for internal corro-
sion control. Corrosion inhibitors consist of chemicals that are used in small quantities
to counter corrosion. The impact of inhibitors on water quality and their effectiveness