Prestressed concrete cylinder pipe (PCCP) used for water and sewer transmission service is composed of a thin wall steel cylinder, lined on the interior and exterior with cement mortar, and reinforced by prestressing wire either wrapped around the steel cylinder or embedded in the exterior mortar (Figures 1 and 2). These large-diameter composite pipes are often thought to be immune to corrosion because the steel cylinder and prestressing wire are covered by concrete whose alkalinity promotes the formation of a protective passive film on the steel surfaces. As with many passive films, however, the protective film is subject to breakdown by chlorides, and there has been an increasing number of failures on PCCP piping because of chloride attack. Once the film is penetrated and corrosion is initiated on the prestressing wires, which are typically under -200 ksi (1,400 MPa) tension, stress corrosion cracking occurs, often causing catastrophic failure of a major water transmission main.
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