Concrete Pipes Strengthened with Carbon Fiber Reinforced Polymer (FRP) for Nuclear Power Plant

This is among the earliest applications where Carbon FRP was used to repair and strengthen a PCCP pipe. Large-Diameter Prestressed Concrete Cylinder Pipes (PCCP) are widely used in the U.S. to carry water and sewage. The construction of these pipes consists of many layers of steel and concrete, including high-strength steel wires that are prestressed in the hoop direction. 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, the only technique that increases the strength of the pipe is the use of FRP.

What sets the PipeWrap™ system apart from other liners is the tremendous strength that it adds to the pipe; in many cases, the strength of the pipe can be increased significantly beyond the original pipe.

• Increases wall thickness by less than ¼ in.
• Restores hoop and longitudinal strength
• Reduces drag friction in the pipe
• Can increase pipe strength beyond original design
• Stops leaks
• Access through manhole is sufficient
• Resilient to harsh chemicals and effluent

Among the clients of PipeWrap™ is 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. After evaluating all options, FRP was selected as the method to strengthen these pipes.

During an on-site demonstration to show the effectiveness of FRP, the steel strands in a new "good" pipe were intentionally cut to model a pipe in which the strands have been lost due to corrosion. The weakened pipe was wrapped with carbon fabric (CFRP), its ends were capped with steel plates and the pipe was pressurized.

Testing was stopped when the pressure in the pipe strengthened with carbon FRP exceeded the original design strength of the pipe.

This clearly demonstrated the feasibility of the use of carbon FRP to strengthen PCCP pipes.

A major concern for most pipe repair projects is the time required to complete the repair. One of the advantages offered by QuakeWrap is the knowledgeable principals who can provide custom solutions for many clients. In the case of Nuclear Generating Station, for example, PipeWrap™ was the only vendor that could design and construct a special heavy carbon fabric (CFRP) with sufficient strength in the longitudinal and hoop directions. This CFRP resulted in lowering the number of wraps in the pipe from 5 layers to 3 layers, leading to significant shorter construction time. This was a major advantage to the client, considering the limited number of shut-down days they have available each year.

Our tack coat is a thixothropic epoxy with high viscosity.

As part of the approval process, it was demonstrated that a single coat of J200TC applied to the surface of the pipe is strong enough to support the weight of three layers of the very heavy PipeWrap™ carbon fabric (CFRP) that QuakeWrap had specially designed and manufactured for this project.

With all these assurances in place, the actual field installation of CFRP began.

The primer, resin was first applied in a thickness of approximately 8 mil to the interior surface of the pipes.

Next, the two-component tack coat was mixed using a mixer and applied to the primed interior surface of the pipes with a thickness of about 40 mil.

At the same time, the two-component saturating resin was mixed. This resin was introduced into the Saturation Machine, and the dry fabric was uniformly saturated with the resin. The saturated fabric was wrapped around the take-up reel and cut to the desired length. The fabric was passed into the pipes through manholes.

The saturated fabric was applied to the interior surface of the pipes that was coated with tack coat. The edges and overlaps of the fabric were carefully finished. One to three layers of fabric were installed on top of one another, based on the design requirements.

Once the strengthening of the pipes was completed, two layers of specially developed, highly chemically resistant QuakeBond™ were applied to the interior surface of the pipes. These were used to further protect the PipeWrap™ system against potential damage from the chemicals present in the gray water.