GPS PE Pipe Systems has supplied plastic piping to carry out one of the longest pipeline pull back schemes ever carried out in Europe: the Orkney to Shapinsay under sea link.

Located two miles off the coast of Orkney Mainland, Shapinsay has just one village and a population of around 300. Historically, the drinking water supply for the island has been provided by seven boreholes but only three of these remain operational and to safeguard the quality and security of supply, Scottish Water decided to connect Shapinsay

to the water treatment works on the Mainland. The project involves installation of 1.4km of pipework on Shapinsay, 4km of pipework on the Mainland and a 2km tunnel under the sea connecting the two islands.

Following a rigorous procurement process, Scottish Water Solutions, the project delivery arm of Scottish Water selected contractor, George Leslie Ltd, to carry out the project. Working with their specialist subcontractor, Stockton Drilling Ltd, they drilled the 311mm diameter tunnel for the 180mm PE pipe from coast to coast 20m below the sea bed, using directional drilling to divert the tunnel up to 15m below the rock head where required. PE pipe was specified with a high wall thickness of SDR6 to ensure sufficient tolerance to the stresses involved during the pull back

Explains Scott Rowan from George Leslie Ltd:

"The maximum water pressure once the pipeline is in use will be in the region of 10 bar, but the stress on the pipe walls during the pull back operation will be extreme. PE pipe was specified for its durability and flexibility as it will need to follow the contours of the tunnel and have a long and maintenance-free service life.

“GPS PE Pipe Systems was the only UK based pipe specialist that could answer the specification for SDR6 PE100 pipe and we were impressed not only with the quality of the piping they provided, but also with the way in which they answered the logistical challenges of such a remote location."

Ten metre sections of piping were butt fused by the George Leslie team to create a 2km string weighing 28 tonnes, which was then laid out straight to enable pressure testing to be carried out prior to the pull back operation. Once the tunnel was completed, the end of the pipe string was connected to the towing head using drill rods and the two day operation to pull it back through the tunnel at the rate of nine metres per minute began.

The undersea pipeline is now in place and the installation team has begun the open cut installation of the land-based pipeline. Shapinsay is expected to get its first taste of water from the Mainland when the full system is completed and commissioned in December 2012.

For more information:

GPS PE Pipe Systems
St Peters Road
Huntingdon
Cambridgeshire
PE29 7DA

Web: www.gpsuk.com