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FRP Penstock Piping

Industry Served: Power


In the last quarter of 2012, RPS Composites completed an FRP penstock (an enclosed pipe delivering water to hydraulic turbines) project for Nova Scotia Power (NSP) replacing 3500 feet of wood stave pipe. This installation is part of a 5-year capital replacement program by NSP with the longer term goal of producing 40% of all power from renewable resources by 2020.

Over the years, the wood stave pipe experienced numerous leaks, requiring expensive repairs. The line has been in operation since the mid 1950s and it was past its normal working life. The pipe was installed at the St. Margaret's Hydro system, which encompasses Tidewater and Sandy Lake hydro stations, a critical component of the power grid serving the city of Halifax Nova Scotia and surrounding communities.

The fiberglass reinforced plastic (FRP) pipe was chosen over high density polyethylene pipe. FRP was chosen for several reasons – competitive pricing, previous successful FRP penstock installations, and location. FRP is more economical than HDPE, particularly in larger diameters. RPS Composites manufacturing facility in Mahone Bay Nova Scotia is only 45 minutes from the St. Margaret's Hydro plant resulting in significant additional savings on freight. RPS Composites has previously supplied several penstocks to NSP dating back to the 1960s and the trouble free performance of these systems has demonstrated the viability of FRP for large diameter piping applications. RPS scope of work included design of the FRP penstock, manufacturing of 2,900' of 10' diameter and 600' of 8' diameter, and design and installation of tie in joints between the FRP and steel thimbles at the damn and turbine intakes. The pipe comprised a 0.06" corrosion barrier and a filament wound structure utilizing Ashland Chemical's Aropol Q6023 resin. The wall thickness of the 10' pipe was 0.74" and the 8' was 0.62". Production of the pipes consumed 330,000lbs. of resin and 550,000 of glass reinforcements. The 40' lengths of pipe were supplied with integral bell and spigot ends with a double "O" ring configuration. The FRP penstock was joined to the steel thimbles by a laminated joint with steel bands clamped over the cured joint to prevent disbonding which may occur due to differential thermal expansion of the steel and FRP. This joint design has been used successfully by RPS on penstocks dating back to the 1970s. The pipe was designed to accommodate a partially buried installation. In this design the pipe is laid on the ground and back fill is installed and compacted in a series of lifts until it is just above the spring line of the pipe with the back fill sloping away from the pipe for drainage.

The project began in May 2012 and the installation was complete in October 2012. This project is an excellent example of RPS value proposition of supplying customers with smarter choices. Our experience in the design and manufacture of large diameter FRP piping allowed Nova Scotia Power to fully realize the benefits of composite materials.









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