JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 20

pipe

Optimal penstock routing
with GRP pipe systems

From an economic and ecological perspective,
the importance of hydropower is definitely
on the rise as it provides an array of
advantages compared to other conventional
methods of power generation.

By
Alexandra Dobnigg
Marketing Graphics & Press
Hobas Engineering GmbH

D

espite the initial
investment obstacle,
small hydropower
plants prove cost-effective
thanks to their long service
life of often more than 70
years and low maintenance
costs. Dams, canals, intakes
and penstocks obviously
cost a very different share of
the total for different sites.
A lot depends on the topography and the geology, but

also on the construction
method and the materials.
The penstock often constitutes a major expense in the
total budget, as much as 40
% is not uncommon in high
head installations and it is
therefore worthwhile choosing the material carefully in
regard to surface roughness,
design pressure, jointing
method, weight and ease of
installation, service life and
maintenance. The tradeoff is between head loss
and capital cost. Regarding
penstock design, there is,
however, a possibility to
save without compromise:
curved Hobas GRP pipe
installation with fewer or no
fittings.

to access, the topography does not allow a fully
straight pipe line, which for
sure would be beneficial
for the hydraulic properties
(low head loss).
The constructors are
confronted with both horizontal and vertical curves
which can be realized with
conventional elbows or
alternatively by curved installation with, for instance,
shorter angular cut pipe
sections and flexible joints
which accommodate a deflection that is higher than
what relevant GRP product
standards provide.

Economic and
hydraulic benefits
While some deflection can
be accommodated in the
Hobas FWC joint to achieve
curves with larger radii,
shorter pipe sections will

produce smaller ones, and
angular cut pipes will reduce
the radii even further,
especially in larger diameter lines. The penstock,
mounted above ground on
saddles or installed underground, is this way optimally routed, and utilizes fewer
or no fittings and concrete
thrust blocks. Regarding the
often remote and difficult
to access construction sites,
every cast in-situ concrete
block that can be eliminated from the design represents substantial cost and
time savings. Besides the
above mentioned economic
benefits, curved installation,
angular cut or not, substantially increases the pipe's
efficiency for there are less
hydraulic losses than if
elbows are employed.

Quality assurance
To check the leak tightness

Curved installation
Since penstocks of small
hydropower plants are often
set in remote places which
are sometimes also difficult

Main components of a small hydropower plant scheme

20 jec composites magazine / No85 November - December 2013
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013

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