Project Highlights
- Composite system repair avoided expensive and extended plant shutdown
- The final solution materials were extensively tested and analyzed by customer and our engineering teams
- A high temperature composite system was installed during normal operations
Project:
Structural and integrity reinforcement of secondary bypass duct from furnace.
Severe corrosion of carbon steel hot gas duct resulted in the 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.
Solution:
Alternative high temperature resins and materials were identified and proposed to create an insulating barrier layer prior to application of carbon fiber, a CFRP repair might provide a structural and integrity repair that could be installed without a plant shutdown.
Working with our engineering and materials partners, SCG developed a testing protocol 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 alternative materials were prepared 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 rising curing process, as materials were force cured during duct operation.
Results:
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.