TPi January 2017

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business & market news
16 TUBE PRODUCTS INTERNATIONAL January 2017
Bespoke pipe puller aids
multi-duct installation
in Ireland
During April 2016, Stockton Drilling Ltd
(SDL) commenced work on a challenging
crossing of the River Corrib in Galway,
Ireland. The work was completed on a
sub-contract basis for GMC Utilities, the
principle contractor for SSE in Ireland.
The project involved the installation of a
390m-long HDPE pipe bundle beneath
the river to facilitate the installation of a
110kV grid connection to the SSE wind
park west of Galway city. To complete
the work SDL utilised its 250-tonne
horizontal directional drilling rig to install
a bore of 710mm (28") diameter into
which the HDPE pipe bundle was to be
pulled. The HDPE pipe bundle consisted
of three 200mm diameter and three
125mm diameter pipes. The installation
took place at a site located close to the
historic Menlo Castle.
As well as having a width of approxi-
mately 110m, the Corrib flows along a
fault line where two rock types, granite
and limestone, converge. The area is
also a Special Area of Conservation
(SAC). These factors, combined with
works being required not to interfere
with the ongoing activities of the
National University of Ireland Galway
and not to disturb the ruins of the
medieval castle, resulted in the project
presenting an array of logistical and
technical challenges.
In order to overcome these challenges,
the HDD profile was designed as a
continuous curve from the entry point,
entering at 13° to the horizontal and
following a vertical radius of not less
than 400m. To facilitate the reaming
stages of the main bore, two pilot holes
were drilled. Both were installed utilising
a 170mm (6¾") diameter down-hole
mud-motor, powering a 216mm (8½")
diameter tri-cone drill bit to follow the
predetermined profile trajectory to the
pre-planned exit point.
The first pilot hole had a 125mm HDPE
pipeline inserted; this was to be used as
a drilling fluid return line during the main
bore reaming operations. The second
pilot bore was reamed in two stages
to the required 710mm (28") diameter
to facilitate the insertion of the HDPE
pipeline bundle.
In order to install the required pipe
bundle effectively, given the pipe sizes
involved there was a requirement for
a pipe towing head that would pull in
five pipes (3 x 200mm and 2 x 125mm)
at the same time. SDL approached
Pipe Equipment Specialists Ltd (PESL)
for assistance, as this is one of the
company’s specialist areas of operation.
PESL offers a variety of pipe pullers
for various aspects of the pipeline and
trenchless industries. The company’s
Multi Puller is a cone-shaped device
that, within the outer shell, has the
facility to install links to which individual
pipe towing heads can be attached.
However, the job was not going to turn
out to be quite so simple.
Subsequent to the first meeting and the
formulation of the design of the Multi
Puller, SDL added that it wanted to
ballast the pipes in the bundle during
the pull-in operation in order to reduce
the pulling loads, and to minimise
stresses on both the drilling rig and
pipes themselves as the installation
proceeded. Further complicating the
situation, the ballasting would not be
required until the pipe string was about
half way through the pull-in operation of
the HDD process.
Steve Kent, managing director of PESL,
came up with the idea of using the
company’s Test Ends which, when
suitably modified, could be utilised in
the place of standard towing heads.
The Test Ends comprise a pipe end
stop that can be inserted into a pipe
The drill rig launch site on the Galway project showing the pipe bundle
successfully completed pull back
The exit side of the bore showing the pipe
bundle about to be installed