Prospect Tarbert Internal Pipeline Assessment

Tender description

The Prospect Tarbert is a high voltage 220kV circuit. It was originally constructed in 1977, energised in 1978 and operated as the Cashla Tarbert 220 kV line until 1986, when the Prospect 220kV Station was commissioned. The circuit is approximately 10.1km in length and consists of an overhead line section and a section of cable crossing the River Shannon. The length of the overhead line section is 7.6 km and the marine cable section is 2.5km. The Prospect Tarbert cable is a High Pressure Fluid Filled Cable (HPFF). At the time of construction, two pipelines were laid across the estuary of the River Shannon from Tarbert Generating Station in Co. Kerry to Kilkerin Point in Co. Clare. Both pipelines are known to be a carbon steel composite covered in a polyethylene layer and casted with a 25-37mm thick mesh reinforced concrete applied to the submarine section of the cable. The two carbon steel pipelines have diameters of 273.00mm and wall thickness 9.3mm with ‘Pritec’ extruded polyethylene anti-corrosion coating of 1.27mm nominal thickness. The Northern pipeline contains the 220kV cable circuit, which is composed of three individual phase cables of 88 mm diameter. The area between the cables and the pipe is filled with electrical insulating oil, which is maintained at a pressure of 15.2 bar. The Southern Pipeline was installed as a spare and is filled with nitrogen. The two pipelines are two meters apart on the riverbed although it is possible that some movement may have occurred due to estuarine conditions. The pipeline internal/external survey shall provide EirGrid with an overall Pipeline Condition Assessment of the Southern Pipeline to enable future use and estimated lifespan.