NH Penstock Pipeline Replaced With Fiberglass Pipe

November 2008 Vol. 63 No. 11

Meandering through New Hampshire’s White Mountains, a large wooden penstock pipeline served as the main water supply for a local hydro facility, Jackman Station.

The facility is fed by the Franklin Pierce Reservoir, which was created by the hydro facility’s dam and surrounding earthen dikes. The water elevation in the reservoir is managed according to spring run-off.

Public Service of New Hampshire (PSNH), the Granite State's largest electric utility, serves more than 475,000 homes and businesses. PSNH’s power generation facilities consist of nine hydroelectric plants, including the Jackman Hydro station, which was built in 1926. This facility, located in Hillsborough, has been serving the area for years, but the penstock was approaching the end of its service life.

Prior to the recent improvements, 5,000 feet of wood stave penstock extended from the Franklin Pierce reservoir to a surge tank upstream of the powerhouse. This 7.5-foot diameter penstock was made up of vintage wood stave sections, circa 1926. Repairs were undertaken in 1954 and in the 1970s, yet the downstream sections of the wood penstock still leaked badly. This leakage caused icing problems during winter months and required constant maintenance. In 2003, the penstock had a significant rupture that impacted abutting properties. To prevent future failures and ensure reliable operations of the hydro facility, repairs to the existing penstock were necessary. In a series of contracts, PSNH decided to replace the remaining wood stave penstock with a new pipeline.

Kleinschmidt Energy & Water Resource Consultants, headquartered in Pittsfield, ME, was retained to develop a feasibility study and engineer a replacement pipeline. Kleinschmidt initially evaluated five pipe material options for the penstock replacement: wood stave, concrete, HDPE plastic, steel and fiber reinforced polymer (FRP). Factors that led to the final determination included the structural reliability, corrosion resistance, hydraulic capacity, ease of installation (pipe weight) and performance history of the pipe material. Kleinschmidt provided their evaluation and recommendations to PSNH, which chose the fiberglass pipe option and purchased CCFRPM pipe manufactured by Hobas Pipe USA of Houston.

Flexibility