Pre-stressed concrete cylinder pipe (PCCP) has been a widely utilized composition of large-diameter pipe for nearly a century due to its economic advantages. First introduced as a lower-cost alternative to full steel or concrete pipe, it has been extensively used in water and wastewater applications. Its use also extends to industrial environments like power plants, where large quantities of circulating water, water intakes, or cooling pipes are required.
What is Pre-Stressed Concrete Cylinder Pipe?
Pre-stressed concrete cylinder pipe is a large-diameter concrete-steel hybrid pipe that was first introduced in 1942. Its composition features a concrete core reinforced with a thin steel cylinder. The steel cylinder is wrapped with high-tensile pre-stressed wires under extreme tension (upwards of 200,000 psi) and externally coated with a cement-rich mortar coating.
The design of PCCP allows for a thinner pipe wall overall than pure reinforced concrete. This is because its design successfully combines the strong tensile properties of steel with the compressive properties of concrete. The extreme tension of the pre-stressed wires allows the pipe to withstand substantial internal pressures as well as external loads. The combined properties of the steel and concrete form a high-strength, long-lasting structure.
PCCP is designed to withstand a dynamic combination of internal pressure and external loads. The concrete core bears the internal load, while the pre-stressed wires balance the internal and external stresses of the pipe. The steel cylinder primarily acts as a water barrier between the concrete core and mortar coating. The external coating protects the entire system from damage or external corrosion. PCCP systems are considered rigid pipe by design, which means they do not need to be buried or depend on soil side support.
Advantages and Precautions for PCCP Applications
The efficient use of materials in PCCP results in a cost-effective, lighter alternative to pure concrete pipe. Cost savings are especially significant for large-diameter pipe applications because of the high volume of materials used in construction. When properly constructed, the engineering principles that underpin PCCP design are sound and result in a long-lasting, high-performing structure. However, when insufficient safety factors are employed during construction, problems occur, which can result in catastrophic collapse of the pipe.
Common Causes of PCCP Failures
Loss of containment within PCCP systems typically results from either degradation of the concrete or, more commonly, failure of the pre-stressed wires. These wires are critical to the system’s function, and localized breaks leave the pipe vulnerable to catastrophic collapse. When localized failures of the pre-stressed wires occur, the surrounding wires cannot carry the tension of the damaged section, which leads to a widespread progressive breakdown of the system and decompression of the concrete core. PCCP failures can easily result in rapid excavation of sinkholes through extensive flooding. Many historical PCCP failures can be traced back to insufficient thickness of the reinforcing pre-pressed wires.
Case Study: Catastrophic San Francisco Water Main Failure in 1999
While PCCP regulations and construction standards have significantly improved since the 1970s, the consequences of improper construction during that era are far-reaching. Efforts to cut PCCP construction costs in the 70s broadly impact municipalities today and are projected to cost water systems billions in the future.
The Metropolitan Water District (MWD), serving 19 million residents of Southern California, experienced these consequences firsthand in December of 1999.
A water main on the outskirts of Irvine, California failed, spilling five million gallons of water and disrupting service to around 700,000 residents of southern Orange County. This failure, which left some without water service for more than a week, exposed critical weaknesses in the MWD system. The failure prompted the district to initiate full-scale inspections to trace its cause. Hundreds of leaks and breaks were discovered during the inspections, caused by premature deterioration of the prestressed wires in the PCCP system.
The financial implications were massive: the water system consisted of at least 100 miles of PCCP, and the total cost of restoration is expected to exceed $2.5 billion over the next 20 years [Source: Los Angeles Times].
Inspection Methods for PCCP Systems
Accurate inspection of PCCP is an essential practice for proper system maintenance and protection against the threat of catastrophic failures. Today, technologies exist to determine the strength and quality of the pre-stressed wires in pipelines. Electromagnetic inspection, which involves running a device through the inside of the pipeline, counts the approximate number of wire breaks present in the line. This form of inspection is an excellent tool to prioritize maintenance and gauge the system’s overall health. Additionally, acoustic fiber optic (AFO) cables can be installed throughout the length of the pipeline without disrupting service. These cables listen for wire breaks and can alert the operator in real time about potential areas of worry.
Repair Methods of PCCP Systems
Isolated repairs of PCCP systems are difficult to implement without full system replacement. Because the pre-stressed wire spans the length of the pipeline, section replacement is difficult without compromising the functionality of the entire system. A total system replacement is an effective but expensive method of repair.
An alternative repair method is slip lining. This involves the insertion of a secondary pipe into the original host pipe. The annulus between the host pipe and the secondary pipe is sealed with grout. This rehabilitation method reduces the total capacity of the line but is an effective way to restore its structural integrity. It also removes the catastrophic failure mechanism present in the host pipe because it is isolated from internal pressure. However, slip lining requires a large run of pipe to be economically feasible and often requires excavation of the pipe segment to insert the slip liner, adding further expense and complexity.
External tendon repair is an effective but expensive method of rehabilitation that can be implemented without taking the pipe out of service. This repair method ensures that the concrete core remains in compression even if the pre-stressed wires fail, reducing the possibility of catastrophic system failure [Source: Dewberry].
A final method of repair includes carbon fiber reinforcement of the PCCP system, which is explored below.
Internal Carbon Fiber Reinforcement of PCCP Systems
Carbon fiber repair is an effective method of internally reinforcing damaged PCCP systems. This method requires the pipe to be drained before a reinforcing composite wrap is applied to its interior. Like slip lining, the carbon fiber wrap acts as a structurally independent pipe within the existing host pipe and eliminates the risk of catastrophic failure. However, carbon fiber application requires no grout or sealant, allowing the pipe to retain much more of its original capacity than slip lining, which noticeably reduces the line’s diameter. The repair mirrors the contour of the pipe, effectively repairing straight sections, elbows, tees, or diameter changes
Internal carbon fiber reinforcement can be used to repair PCCP systems regardless of the level of degradation of the pipe and wires. Whether the system is at risk for catastrophic collapse, or the damage is isolated to a single joint failure, carbon fiber repairs are both an economical and effective solution for any scale of repair. The biggest benefit of carbon fiber repairs is that all reinforcement is internal, meaning no additional access points are needed, and no pipe excavation is required.
Advanced FRP Systems has extensive experience implementing carbon fiber repairs for PCCP systems that need structural reinforcement. We work hand in hand with our customers to design, calculate, and implement cost-effective composite repair solutions. To learn more about how carbon fiber reinforcement can cost-effectively rehabilitate your PCCP system, schedule a free consultation.
Where Tension Meets Compression: Applications of Pre-Stressed Concrete Cylinder Pipe
Pre-stressed concrete cylinder pipe (PCCP) has been a widely utilized composition of large-diameter pipe for nearly a century due to its economic advantages. First introduced as a lower-cost alternative to full steel or concrete pipe, it has been extensively used in water and wastewater applications. Its use also extends to industrial environments like power plants, where large quantities of circulating water, water intakes, or cooling pipes are required.
What is Pre-Stressed Concrete Cylinder Pipe?
Pre-stressed concrete cylinder pipe is a large-diameter concrete-steel hybrid pipe that was first introduced in 1942. Its composition features a concrete core reinforced with a thin steel cylinder. The steel cylinder is wrapped with high-tensile pre-stressed wires under extreme tension (upwards of 200,000 psi) and externally coated with a cement-rich mortar coating.
The design of PCCP allows for a thinner pipe wall overall than pure reinforced concrete. This is because its design successfully combines the strong tensile properties of steel with the compressive properties of concrete. The extreme tension of the pre-stressed wires allows the pipe to withstand substantial internal pressures as well as external loads. The combined properties of the steel and concrete form a high-strength, long-lasting structure.
PCCP is designed to withstand a dynamic combination of internal pressure and external loads. The concrete core bears the internal load, while the pre-stressed wires balance the internal and external stresses of the pipe. The steel cylinder primarily acts as a water barrier between the concrete core and mortar coating. The external coating protects the entire system from damage or external corrosion. PCCP systems are considered rigid pipe by design, which means they do not need to be buried or depend on soil side support.
Advantages and Precautions for PCCP Applications
The efficient use of materials in PCCP results in a cost-effective, lighter alternative to pure concrete pipe. Cost savings are especially significant for large-diameter pipe applications because of the high volume of materials used in construction. When properly constructed, the engineering principles that underpin PCCP design are sound and result in a long-lasting, high-performing structure. However, when insufficient safety factors are employed during construction, problems occur, which can result in catastrophic collapse of the pipe.
Common Causes of PCCP Failures
Loss of containment within PCCP systems typically results from either degradation of the concrete or, more commonly, failure of the pre-stressed wires. These wires are critical to the system’s function, and localized breaks leave the pipe vulnerable to catastrophic collapse. When localized failures of the pre-stressed wires occur, the surrounding wires cannot carry the tension of the damaged section, which leads to a widespread progressive breakdown of the system and decompression of the concrete core. PCCP failures can easily result in rapid excavation of sinkholes through extensive flooding. Many historical PCCP failures can be traced back to insufficient thickness of the reinforcing pre-pressed wires.
Case Study: Catastrophic San Francisco Water Main Failure in 1999
While PCCP regulations and construction standards have significantly improved since the 1970s, the consequences of improper construction during that era are far-reaching. Efforts to cut PCCP construction costs in the 70s broadly impact municipalities today and are projected to cost water systems billions in the future.
The Metropolitan Water District (MWD), serving 19 million residents of Southern California, experienced these consequences firsthand in December of 1999.
A water main on the outskirts of Irvine, California failed, spilling five million gallons of water and disrupting service to around 700,000 residents of southern Orange County. This failure, which left some without water service for more than a week, exposed critical weaknesses in the MWD system. The failure prompted the district to initiate full-scale inspections to trace its cause. Hundreds of leaks and breaks were discovered during the inspections, caused by premature deterioration of the prestressed wires in the PCCP system.
The financial implications were massive: the water system consisted of at least 100 miles of PCCP, and the total cost of restoration is expected to exceed $2.5 billion over the next 20 years [Source: Los Angeles Times].
Inspection Methods for PCCP Systems
Accurate inspection of PCCP is an essential practice for proper system maintenance and protection against the threat of catastrophic failures. Today, technologies exist to determine the strength and quality of the pre-stressed wires in pipelines. Electromagnetic inspection, which involves running a device through the inside of the pipeline, counts the approximate number of wire breaks present in the line. This form of inspection is an excellent tool to prioritize maintenance and gauge the system’s overall health. Additionally, acoustic fiber optic (AFO) cables can be installed throughout the length of the pipeline without disrupting service. These cables listen for wire breaks and can alert the operator in real time about potential areas of worry.
Repair Methods of PCCP Systems
Isolated repairs of PCCP systems are difficult to implement without full system replacement. Because the pre-stressed wire spans the length of the pipeline, section replacement is difficult without compromising the functionality of the entire system. A total system replacement is an effective but expensive method of repair.
An alternative repair method is slip lining. This involves the insertion of a secondary pipe into the original host pipe. The annulus between the host pipe and the secondary pipe is sealed with grout. This rehabilitation method reduces the total capacity of the line but is an effective way to restore its structural integrity. It also removes the catastrophic failure mechanism present in the host pipe because it is isolated from internal pressure. However, slip lining requires a large run of pipe to be economically feasible and often requires excavation of the pipe segment to insert the slip liner, adding further expense and complexity.
External tendon repair is an effective but expensive method of rehabilitation that can be implemented without taking the pipe out of service. This repair method ensures that the concrete core remains in compression even if the pre-stressed wires fail, reducing the possibility of catastrophic system failure [Source: Dewberry].
A final method of repair includes carbon fiber reinforcement of the PCCP system, which is explored below.
Internal Carbon Fiber Reinforcement of PCCP Systems
Carbon fiber repair is an effective method of internally reinforcing damaged PCCP systems. This method requires the pipe to be drained before a reinforcing composite wrap is applied to its interior. Like slip lining, the carbon fiber wrap acts as a structurally independent pipe within the existing host pipe and eliminates the risk of catastrophic failure. However, carbon fiber application requires no grout or sealant, allowing the pipe to retain much more of its original capacity than slip lining, which noticeably reduces the line’s diameter. The repair mirrors the contour of the pipe, effectively repairing straight sections, elbows, tees, or diameter changes
Internal carbon fiber reinforcement can be used to repair PCCP systems regardless of the level of degradation of the pipe and wires. Whether the system is at risk for catastrophic collapse, or the damage is isolated to a single joint failure, carbon fiber repairs are both an economical and effective solution for any scale of repair. The biggest benefit of carbon fiber repairs is that all reinforcement is internal, meaning no additional access points are needed, and no pipe excavation is required.
Advanced FRP Systems has extensive experience implementing carbon fiber repairs for PCCP systems that need structural reinforcement. We work hand in hand with our customers to design, calculate, and implement cost-effective composite repair solutions. To learn more about how carbon fiber reinforcement can cost-effectively rehabilitate your PCCP system, schedule a free consultation.