Strengthening of Pipes with Carbon Fiber Reinforced Polymer (CFRP)
QuakeWrap wet layup is an economical CFRP system for strengthening corrosion-damaged pipes. Specially-designed bands of carbon fiber reinforced polymer (CFRP) fabric are applied to the surface of the pipe, significantly increasing the strength of the pipe. Application of CFRP virtually leaves the internal diameter of the pipe unchanged. Installation is very fast and economical.
Large-diameter pre-stressed concrete cylinder pipes (PCCP) are widely used in the U.S. to carry water and sewage. PCCP consists of a steel cylinder embedded in a concrete core, which is helically wrapped with high-strength, hard-drawn wire after curing. The wire is embedded in a thick cement slurry and coated with a dense cement mortar. An easily assembled watertight joint is provided by using bell and spigot steel joint rings welded to the ends of the cylinder and sealed with a confined round rubber gasket.
Corrosion of steel reinforcement is a major cause of failure and potential collapse of these pipes. Numerous such collapses have been reported in the U.S. in recent years, resulting in significant loss of property.
A number of solutions and lining systems have been offered in recent years. However, these techniques add little (if any) additional strength to the pipe.
What sets the QuakeWrap system apart from other liners is the tremendous strength that carbon fiber reinforced polymer (CFRP) adds to the pipe. In many cases, the strength of the pipe can be increased significantly beyond the original!
Among the advantages of QuakeWrap are:
- Increases wall thickness by less than ¼ in.
- Restores hoop and longitudinal strength
- Can increase pipe strength beyond original design
- Stops leaks
- Access through manhole is sufficient
- Resilient to harsh chemicals and effluents
Among the clients of QuakeWrap are a number of major utilities, including the largest nuclear generating station, in the U.S. In a number of PCCP pipes in this facility, corrosion of the steel wires had resulted in cracking of the concrete and weakening of the pipes. During an on-site demonstration, the steel strands in a new pipe were intentionally cut to model a pipe in which the strands have been lost due to corrosion. The weakened pipe was wrapped with QuakeWrap® carbon fiber reinforced polymer (CFRP), its ends were capped with steel plates and the pipe was pressurized. Testing was stopped when the pipe pressure exceeded the original design strength of the pipe. This clearly demonstrated the feasibility of this technique.
A major concern for most pipe repair projects is the time required to complete the repair. Our tack coat is a high viscosity thixothropic epoxy. As part of the approval process, it was demonstrated that a single coat of tack coat applied to the surface of the pipe is strong enough to support the weight of three layers of a very heavy carbon fabric; this leads to faster construction time and significantly reduces down time of the system.
The QuakeWrap system can be custom-designed to meet the needs of the clients. For example, in the case of the nuclear power plant, QuakeWrap was the only vendor that could design and construct a special fabric with sufficient strength in the longitudinal and hoop directions. This resulted in lowering the number of wraps in the pipe from 5 layers to 3 layers, leading to significant shorter construction time. In another application for Power Service of New Mexico, we designed and constructed yet another special carbon fabric that could strengthen the pipe with application of a single layer of carbon fabric.
The QuakeWrap system has also been used in repair of 9-ft. diameter PCCP pipes on a section of the Central Arizona Project. In this case, some regions of the pipe that were severely cracked were first patched with strips of carbon fabric before the entire internal surface of the pipe was strengthened with QuakeWrap® carbon fiber reinforced polymer (CFRP) fabrics.
