Prestressed Concrete Cylinder Pipe (PCCP)

The Basics of PCCP

Prestressed Concrete Cylinder Pipe (PCCP) consists of a concrete core, a thin steel cylinder, high tensile prestressing wires, and a mortar coating.

The concrete core is the main structural load-bearing component with the steel cylinder acting as a water barrier between concrete layers. The prestressing wires produce a uniform compressive pressure in the core that offsets tensile stresses in the pipe, and the mortar coating protects the prestressing wires from physical damage and external corrosion.

History of Manufacturing and Use

PCCP was first manufactured in 1942 as lined cylinder pipe. The prestressing wire in lined cylinder pipe is wrapped directly around the steel cylinder.

A second type of PCCP was developed in 1952 that has concrete encasement of the steel cylinder on both sides. Known as embedded cylinder pipe, it differs from lined cylinder pipe by the encapsulation of its steel cylinder in a concrete core. Therefore, the prestressing wire is wrapped around the concrete core rather than the steel cylinder as in lined cylinder pipe.

The typical diameter ranges for lined and embedded cylinder pipe are between 16 to 60 inches (0.4 to 1.5 meters) and 30 to 256 inches (0.75 to 6.5 meters).

The Evolution of PCCP Design

PCCP design and manufacturing standards have gradually developed since 1942 with the first standard for PCCP approved by the American Water Works Association (AWWA) in 1949.

The AWWA C301 Standard for Prestressed Concrete Pressure Pipe, Steel Cylinder Type, for Water and Other Liquids (AWWA C301) standard was revised multiple times with the last revision in 2007.

In 1992, the AWWA created a new standard for PCCP design and manufacturing defined as the AWWA C304 Standard for Design of Prestressed Concrete Cylinder Pipe (AWWA C304).

The initial structural design requirements for the manufacturing of PCCP tended to be conservative with high safety factors. However, as experience with using this composite pipe and understanding of the behavior of PCCP increased, along with advances in material sciences, changes in the structural design of PCCP were made to reduce the cost of manufacturing.

The increase in the tensile strength of the wire during manufacturing in the late 1960s and early 1970s reduced the amount of prestressing steel wire and allowed wire of smaller diameter, which resulted in what appeared to be a more efficient design and economical manufacturing. These practices culminated in the 1970s when pipe utilizing Class IV wire and other cost saving measures were implemented in the manufacturing process.

Problematic Classes of PCCP

Pipe from the 1970s era started experiencing a high rate of premature failures. Subsequently, the engineering standards for PCCP began to improve, resulting in improved standards for PCCP. The major revisions in the standards, design, and manufacturing of PCCP consist of changes in the maximum diameter, the quality (strength) of the concrete, the thickness of the steel cylinder, prestressing wire standards (wire diameter, wrapping stress, spacing, etc.), and the thickness of the mortar coating.

In recent years, several significant improvements in the PCCP manufacturing process and quality control procedures have been brought about by the American Concrete Pressure Pipe Association (ACPPA) and the industry which is represented through:

• A strong focus on quality control and technology development
• A water industry landmark compliance audit and certification program
• Development of rigorous standards

The revised standards have resulted in a pipe material that is better designed and manufactured than the PCCP produced at any time over its 50-year history. PCCP has the lowest water main break rate per 100 kilometers of any other pipe material (Prosser, 1996).

The American Concrete Pressure Pipe Association (ACPPA) reports that 90 out of the 100 largest water utilities in the United States use PCCP in their water systems and the demand for PCCP is steadily increasing for new transmission pipelines.