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 offset tensile stresses in the pipe, and the mortar coating protects the prestressing wires from physical damage and external corrosion.
Prestressed Concrete Cylinder Pipe (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 and 30 to 256-inches, respectively.
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 factors of safety. 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 the PCCP were made to reduce the cost of manufacturing. The increase in the tensile strength of the wire during manufacturing in the late 1960’s and early 1970’s 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 1970’s when pipe utilizing Class IV wire and other cost saving measures were implemented in the manufacturing process.
Pipe from this 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 the PCCP consist of changes in the maximum diameter of the PCCP, 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, a number of 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 result in the revised standards provides a pipe material that designed and manufactured much better than the PCCP produced at any time over its 50-year history.
It is reported by the American Concrete Pressure Pipe Association (ACPPA) that 90 out of the 100 largest water utilities in the United States use Prestressed Concrete Cylinder Pipe (PCCP) in their water systems and the demand for PCCP is steadily increasing for transmission pipelines. Furthermore, PCCP has the lowest water main break rate per 100km than any other pipe material (Prosser, 1996).
- Resistant to physical damage
- Rapidly and economically installed
- Good corrosion resistance
- Can resist high internal pressure and external loading
- Wide range of pipe diameters available (up to 144-inches)
- Typically more economical than properly lined and coated ferrous pipes
- Requires careful installation to avoid cracking
- Susceptible to attack by Hydrogen Sulfide (H2S) and acids when pipes are not coated
MAIN FORMS OF FAILURE IN PCCP
- Broken prestressing wires due to corrosion or poor material quality
- Joint leaks
- Poor bedding
- Excessive external loading
- Hydrogen sulfide (H2S, wastewater applications)
- Poor quality mortar coating
- Corrosive environment (corrosive/ aggressive soil)
- Construction damage (coating damaged and not repaired)
CONDITION ASSESSMENT OF PCCP
Large diameter prestressed concrete cylinder pipelines (PCCP) are a significant investment for many water and wastewater agencies. Assessing and monitoring the condition of these pipes is becoming an increasingly important and challenging task. Pure has a comprehensive suite of services to better understand the condition of and manage PCCP mains.
- Engineering Services
- Structural Assessment
- Wire Break Monitoring
- Pressure Transient Monitoring
- Pipeline Management Programs
- Leak Detection
- Structural Analysis
- Visual & Sounding Inspections