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HydroVision International 2017
18 HYDRO REVIEW / June 2017 www.hydroworld.com
• Replacing both penstocks with two 10-foot-diameter fberglass
reinforced penstocks; and
• Rehabilitating the existing penstocks and foundations.
Evaluations focused on four possible replacement materials — steel,
concrete, high-density polyethylene and fberglass.
“Te alternatives analysis report provided to FirstLight by Gomez
and Sullivan recommended either an in-kind replacement of the existing
steel pipe or replacement with new fberglass pipe,” said Ben Sawyer,
a civil and structural engineer with Gomez and Sullivan. “FirstLight
selected the fberglass replacement alternative because that alternative
was the most cost-efective option that still provided a similar amount
of net generation compared to the existing confguration.”
Fixing the problem
Having chosen a solution, FirstLight then had to pick a supplier. Hobas
Pipe USA of Houston was selected after previously performing work on
its Rocky River project. Te selection criteria included: quality control/
quality assurance program, uniformity of product, coupling sealing
surface, assembly technique, joint testing, interior and exterior smooth
fnish, domestic manufacturing facility, proven at large diameters and
wall thickness and, last but not least, engineering technical assistance.
The penstocks were replaced between September 2015
and January 2016 with 10-foot-diameter centrifugally-cast,
fiberglass-reinforced, polymer mortar (CCFRPM) pipe.
Hobas manufactured 600 feet of this CCFRPM pipe for this replacement project.
Installation posed its own challenges. Te steep job site was located
in a remote area with a section of the penstock running under an
existing highway bridge with low overhead clearance. It was also
necessary to construct a temporary road and crane pad to access the
penstock replacement area from midway along its route from the
forebay to the powerhouse.
An ingenious on-site transportation device used to install the pipe
under the bridge was designed by the contractor, Bancroft Contracting
Corp. of South Paris, Maine.
“Te rig involved a long I-beam connected to a column,” Sawyer
said. “Te column was composed of two hollow steel square tubes with
one sliding inside the other and held in place with steel pins. Wheels
were attached to the bottom of the column.
“Te end of the beam not connected to the column was attached to
the arm of an excavator, which could then drive the rig through a section
of pipe and extend the column to lift the pipe of the ground. Ten
the rig was driven up to an installed section of pipe and the column
could be lowered to drive the rig into the installed pipe, butting the
new section of pipe against the installed section.”
Te new penstocks were partially buried two feet above the spring
line, utilizing no cradles for support to optimize installation cost. Te
fll material was placed to about 2 feet above the pipe centerline, leaving
3 feet exposed. Te CCFRPM pipe was designed and manufactured
with an operating pressure of 50 pounds per square inch (psi) to
accommodate the operating pressure of the line.
Te penstock was returned to service during January 2015. ■
Stuart Piermarini is is the Connecticut facilities Plant Manager for FirstLight Power
Resources. Erin Boudreaux is marketing manager for Hobas Pipe USA.
Fill material was placed about 2 feet above centerline on the new penstocks, leaving 3 feet exposed.