Circ. Water Pipe Leaking
Nuclear Generating Station
Pipe leak on section with limited access, where replacement was not an option.
- CW Pipe – 24 Diameter
- Leak near flange
- Previously repaired with other methods as shown.
Repaired pipe with carbon fiber wrap with the following elements:
- Provided Engineering Calculations for repair
- Removed previous repair and prepared surface
- Stopped leaks
- Wrapped pipe with CFRP per engineering drawings
- Inspected and tested final repair
Leak repaired with CFRP on existing pipe section. Repair completed during an outage in a 48 hour timeframe.
Steel Pressurized Water Pipe
CFRP Repair & Testing
Engineers wanted to determine if high strength composites could be used to perform fast, non-intrusive repairs to pressurized steel pipe. A test was designed using a severely damaged piece of 18″ diameter steel pipe. The pipe section had lost wall thickness of 50% to 100% due to corrosion. As can be seen, the pipe was completely corroded through leaving a number of holes including one large 2″ x 4″hole.
First the corrosion was removed using abrasive blasting. The large holes were covered with light gauge sheet metal and attached with silicone caulk. Then, a multi-layer carbon fiber system was applied to the pipe. The system included a galvanic insulator and three layers of heavy ounce fabric. The system was installed wet on wet to simulate field repair conditions.
The pipe section was transported to the plant for testing. Hydro-testing equipment was connected to the pipe segment. Pipe fitters checked all fittings prior to pressurizing the pipe segment treated with carbon fiber reinforcement. After filling the pipe with water, pressure was gradually increased in 50 psi increments with a five minute dwell time at each interval. Once the pressure reached 200 psi, the dwell time was extended to 60 minutes. There was no breech in the carbon fiber reinforcement and there was no pressure drop
The pipe showed no signs of damage or leaking when sustained pressure of 200 psi was applied. The high strength carbon fiber repair system proved to be a viable repair method that would provide ease of installation, replacement strength for the steel lost through corrosion, a water-tight seal under design pressure, and significant new corrosion resistance.
The piping was weathered with about 60% showing signs of rust. The remaining 40% appeared to have tight mil scale. The pipe required cleanup and the application of a protective coating to prevent rust and mil scale.
The repair system used multiple coats and flake to provide a permeation resistant membrane coating to prevent rust and mil scale.
The repair method began with abrading the mil scale with 40 grit sand paper to “roughen” the surface. Next the pipe surface was cleaned with high-pressure water to remove dirt and loose rust. We then applied 1 coat at 5 to 7 mils of a surface tolerant epoxy by brush and roller. For the final step, SCG applied a second coat at 2 to 4 mils of high solids poly-urethane.
Durable repair developed specifically for this environment that met the required shutdown constraints.
9′ Dia. Hot Gas Duct
Strengthening & Rehabilitation
Structural and integrity reinforcement of secondary bypass duct from furnace.
Severe corrosion of carbon steel hot gas duct resulting in danger of structural collapse and through holes causing EPA reportable releases. Replacing duct would cause extended plant shutdown. Corrosion level of existing steel had reached the level where weld repairs created further damage, and support structure was not designed for additional weight of alloy cladding. Replacement and alloy cladding were also price prohibitive for construction costs and not feasible given plant downtime for extended shutdown. Plant had not considered CFRP repairs as traditional systems have temperature limitations of approximately 160-180 degrees F. This duct cycled from approximately 120 degrees F to 440 degrees F when the furnace was in bypass mode.
By using alternative resins for CFRP and utilizing an insulating barrier layer prior to application of carbon fiber, a CFRP repair provides a structural and integrity repair that was installed without a plant shutdown.
Working with our engineering and materials partners, a testing protocol was developed to prove whether the modified CFRP system would retain its structural properties through long term temperature cycling of the duct.
Once the test protocol was complete, samples of the composite system were created and thermally cycled to replicate the plant and duct operating conditions. Post cycling testing actually provided increased structural capacity and no degradation to the system.
Design and Installation Challenges:
After the testing program produced a viable system, the design process included dealing with long sections of duct that were originally designed to be self-supporting but now lacked structural integrity, and to transfer strength of the CFRP system across stiffeners, flanges and ports on the duct.
The entire duct was modeled using both a 3D Finite Element Analysis and Global Beam. Analysis in order to capture the behavior of the duct and to validate the repair strategies.
The installation process was equally complex, as furnace scrams would send the surface temperature of the duct soaring 300 degrees without warning. The plant operation also created significant challenges for the resin curing process, as materials were force cured during duct operation.
The result of the testing, design and successful installation is a first of its kind, Patent Pending system for using CFRP to structurally repair high temperature systems.
The cost of the repair was a fraction of the alternatives in construction cost, and did not require a single day of plant shutdown, providing an immeasurable economic benefit.