Penstock Rehabilitation Using CFRP

In 2012, power output dropped at Mississippi River Power Corp.'s 4.6-MW Brian J. Gallagher Generating Station, on the Mississippi River in Ontario, Canada. The turbine was taken offline inspected and found to be in good condition. Mississippi River Power then examined the 106-inch diameter penstock to discover it was partially blocked. The horizontal steel plate lining the penstock had delaminated in the rectangular transition section, causing the steel liner to buckle and deform throughout the concrete-encased pipe.

Full-out replacement and welding a series of internal steel patch plates onto the concrete encasement with a grouted annulus were considered alternatives for a solution and both ruled out due to a number of reasons including safety and cost concerns.A carbon fiber-reinforced polymer (CFRP) solution, manufactured by Fyfe, Co., was chosen as alternative solution to provide a fully-structural rehabilitation solution.

Designed according to requirements from the American Water Works Association (AWWA), the CFRP liner resists the effects of the internal positive pressure, internal negative pressure, external groundwater pressure and temperature changes without relying on any strength contribution from the encasement. When designing for the top and bottom portions of the transition piece, SGH designed the Tyfo^® Fibrwrap^® system to act compositely with the reinforced concrete section as a one-way slab to resist the combined effects of groundwater pressure and internal negative pressure in flexure. The general requirements of the American Concrete Institute’s 440.2R-08 guide were followed for flexural strengthening with additional limit states investigated, such as CFRP debonding, steel reinforcement yielding and concrete crushing.