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Coatings as Corrosion Control in Water Distribution Systems

Corrosion is the slow decay and deterioration of a substance by chemical action moving inward from the surface.

Corrosion can occur on the inside or outside of the metal surfaces of storage facilities in water distribution systems; however, using a storage tank coating can control corrosion.

Corrosion

There are many factors that can influence the rate of corrosion, including the temperature of water. The warmer the water, the faster the chemical corrosion reactions. If a water is corrosive, low velocities create a longer contact time between the water and pipe, which can result in a higher metal pickup and a higher amount of complaints of dirty water, while high velocities cause rapid pipe deterioration, but little metal pickup.

Corrosion can also be influenced by substances in the water, including dissolved oxygen, carbon dioxide, and salts, and can also occur when mixing waters from different sources and different chemical content.

A primary form of corrosion control is painting the outside or inside of a tank with paint or a coating. This is the most effective way to control corrosion inexpensively and the most important aspect of any corrosion control program. Methods other than painting and coating that are used to control corrosion include adding chemicals to the water treatment process and electrical control.

Most regions require that coatings used in potable water systems be approved by a regulatory body. NSF International publishes two standards to provide guidance, and generally, coatings that are approved for use by the FDA for continuous contact with aqueous foods as defined in the Code of Federal Regulations are generally acceptable to use in a potable water distribution system.