NH Penstock Pipeline Replaced With Fiberglass Pipe

November 2008 Vol. 63 No. 11

“The corrosion resistance and relative stiffness of FRP pipe meant it could be supported on the existing grade and half buried, rather than placed on saddles or completely covered in a buried trench. This design flexibility, combined with a longer projected service life led to a competitive total construction cost for the FRP alternative,” stated Keith Martin, a project engineer and civil/structural engineer with Kleinschmidt.

“The lower frictional resistance of the FRP compared to other materials allowed the replacement pipe to be reduced to a 7-foot diameter without additional head loss,” added Martin.

The pipe was half buried in the shallow trench of the existing penstock, requiring minimal excavation costs and low environmental disturbance. Approximately 300 feet of the new penstock was supported above ground on steel saddles to accommodate the topography as well as minimizing the impact to the wetlands that the penstock crossed.

“HOBAS CCFRPM is manufactured by a unique computer controlled centrifugal casting process. To achieve the higher axial strength necessary for the aboveground installation, additional reinforcement is placed in the longitudinal direction during the manufacturing process,” explained Rene Garcia, Sr. Hobas engineering associate.

“PSNH bought the pipe directly and CCB Inc. of Westbrook, ME, was contracted to install it,” said Newell Porter, project manager with CCB.

Remote challenges

The job site posed some challenges as the pipe was installed in a remote area. “The pipe arrived as scheduled and unloaded near the roadside. This phase of the job called for 1,020 feet of 84-inch diameter pipe. The individual joints were then carried to the point of installation with an excavator. We had no truck access to the installation point. The first part of the installation was through a curve where 10-foot joint sections were connected and then deflected to make up the curve,” stated Porter.