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Corrosion by Natural Waters
Abundant supplies of fresh water are essential to industrial development. Enormous quantities are required for cooling of products and equipment, for process needs, for boiler feed and for sanitary and potable water. It was estimated, in 1980, that the water requirements for industry in the USA approximated 525 billion liters per day. A substantial quantity of this water was reused. The intake of "new" water was estimated to be about 140 billion liters daily. If this water was pure and contained no contaminants, there would be little need for water conditioning or water treatment.
The fast-growing demand for clean, fresh water coupled with the need to protect and enhance the environment, has made many areas of the world vulnerable to water shortages for various human uses.
As they interact with the electricity industry, these uses encompass agricultural irrigation, thermoelectric generation, municipal water and wastewater treatment and distribution, and industrial processes. The dependence of electricity supply and demand on water availability can impede the sustainability of economic growth, adversely affect future growth in electricity demand, cause shortages in current supplies of electricity, and have direct impact on power system planning and expansion.
Water possesses several unique properties, one being its ability to dissolve to some degree every substance occurring on the earth's crust and in the atmosphere. Because of this solvent property, water typically contains a variety of impurities. These impurities are a source of potential trouble through deposition of the impurities in water lines, boiler tubes and on products which are contacted by it.
Dissolved oxygen,
the principal gas present in water, is responsible for costly replacement of
piping and equipment by corrosive attack on metals with
which it comes in contact. The origin of all water supply is moisture that has
been evaporated from land masses and oceans and subsequently precipitated from
the atmosphere. Depending on weather conditions, this may fall in the form of
rain, snow, sleet or hail. As it falls, this precipitation contacts gases comprising
the atmosphere and suspended particulates in the form of dust, industrial smoke
and fumes, and volcanic dust and gases.
According to the American Waterworks Association (AWWA) industry database, there
is approximately 1,483,000 km (876,000 mi) of municipal water piping in the United
States. This number is not exact, since most water utilities do not have complete
records of their piping system. The sewer system consists of approximately 16,400
publicly owned treatment facilities releasing some 155 million m3 (41 billion
gallons) of wastewater per day (1995). The total annual direct cost of corrosion
for the nation?s drinking water and sewer systems was estimated at $36.0 billion.
This cost was contributed to by the cost of replacing aging infrastructure, the
cost of unaccounted-for water through leaks, the cost of corrosion inhibitors,
the cost of internal mortar linings, and the cost of external coatings and cathodic
protection.
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