TPi January 2017

business & market news

Bespoke pipe puller aids multi-duct installation in Ireland

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.

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

The exit side of the bore showing the pipe bundle about to be installed

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

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