Water pipeline from Turkey to Cyprus - 1,600 mm diameter PE 100 pipeline and its flange-technology solution

The construction of the 80 km long drinking-water pipeline through the Mediterranean sets new standards in water supply. Urgently needed by the Turkish Republic of Northern Cyprus (TRNC), it runs from the Turkish mainland (Mersin province) to the Turkish part of the island of Cyprus. Single lengths of 500 m PE pipe are being produced for the TRNC project, and installed tethered to float around 250 m below the surface of the Mediterranean. The otherwise customary seabed installation was not the first-choice solution for this project. One of the reasons was the depth exceeding 1,400 m, interspersed with numerous underwater ridges and trenches, encountered along the installation route.

The plans for this project go back more than fifteen years. The Alaköprü dam at the Turkish side was planned as early as 1998; the installation of the PE 100 pressure pipeline is now merely the conclusion of a long chain of events. Construction of the dam began in the mountains of the province, to the north-east of the Mediterranean town of Anamur, in 2011. The dam is also to be used for the generation of hydroelectric power, as well as storing the water required for the pipeline. From here, the water is transported by pipeline to the Anamur pumping station, and then enters the pressure PE line leading into the Mediterranean. After travelling around 80 km through the sea, the PE pressure pipeline reaches the coast of the Turkish Republic of Northern Cyprus, where the water is pumped into the reservoir of the Geçitköy dam, some 3 km way.

This unique PE project starts in the immediate vicinity of the Taşucu containment basin. Here, the 500 mm lengths of PE 100 pressure pipe sections, with an outside diameter 1,600 mm, have already been under production for many months. Three extrusion machines have been operating in parallel in this purpose-built facility. This system not only achieves cost benefits, but also for many projects, it provides an assurance factor both desirable and in many cases mandatory. The pipe length results from the fact that PE pipes, due to their specific gravity of less than 1 g/cm3, would normally float on the surface of the water. This fact, in combination with the lower relative density of freshwater compared to seawater, causes enormous positive buoyancy forces. These are counteracted by the pipe joining yokes, each consisting of two flanged connectors and a steel pipe bend to which the flanged connector is fixed. The steel yokes have an outside diameter of 1,514 mm, a curvature radius of 8,000 mm with a bend angle of 30°, and weigh around 10 tonnes without the connecting elements. Total weight including the two connecting elements is around 13 tonnes. The steels yokes, which also act as fixing and anchoring points, are subsequently drawn down to a depth of 250 m by means of steel cables and then anchored to the seabed (Figure 1), illustrating even better the special features of this project.

The specially made flange connectors are welded on to the long PE pipes on site and bolted to the steel pipe yokes by means of a steel flange provided specifically for this purpose. This yoke is then anchored to the seabed by means of steel cables to the securing and anchoring point. The challenge for Reinert-Ritz was that of providing a product to join the PE pipes and steel yokes durably and securely such order that even the most adverse conditions encountered underwater in the Mediterranean could not impair the connection. At a depth of around 250 m, this design involves the following technical challenges: buoyancy forces exerted by the PE 100 pipeline; powerful and dynamic sea currents, high shipping (and submarine) traffic frequency, potential of earthquakes, and the 7 bar operating pressure.

Decision for high quality and safety

The Nordhorn company is the specialist for semi-finished products and full pressure rated fittings conforming to the specified pressure classification for large dimensions up to an outside diameter of d 2000 mm; hence the right address for solutions to demanding problems. With over forty years of experience in plastics and the company’s pronounced quality awareness, the definitive arguments are established for initiating the co-operation between the project planner and Reinert-Ritz. From the high-quality granulate, used for production of the semi-finished products, through to the machining of the finished stub ends, the company was able, with its all- encompassing Quality Assurance system, to guarantee the high production standards vital for the performance and completion of this demanding project. This high quality consciousness has been shaped, in particular, by work for the gas industry in Germany, one of the first customers for PE, which makes use of this material and its high flexural strength in areas subject to mining subsidence. Only then did the safety and cost benefits result - within just fifty years - in PE‘s leadership on the supply-systems market.

It is therefore not surprising that ever more positive experience is being accumulated, with the application of PE pressure-pipe systems in large-scale industrial fire-extinguishing installations and power-generation plants, including the nuclear-energy industry.

There are two production routes for these full pressure- rated fittings: injection moulding and machining. The hollow bars and solid rods made by Reinert-Ritz are used in the latter process. This method assures a product free of voids and incorporating more than forty years of design and processing experience.

Solution of the complex flange concept

Production of hollow bars of 1,900/1,400 mm, with a wall thickness of approx. 250 mm, is the first stage in the fabrication of the special flanged connection. Subsequent machining takes place on a milling machine capable of processing material up to sizes of 2,800 x 1,500 x 4,800 mm. A particular challenge was presented by the large dimensions of the PE pipeline fitting and the extremely high dimensional accuracy demanded; tolerances of 0.0 mm and +0.5 mm. On site in Turkey, the finished PE 100 stub end is enclosed geometrically secured in two steel clamping assemblies, into which it must fit perfectly. The high-precision flanged connectors are assembled on a special installation ship, with twenty-four connecting bolts, on both ends of the steel yoke. The yoke is then anchored to the seabed, to enable the pressure pipeline to "float" at an average depth of 250 m.

Conclusion

The precondition for the success of this project was the successful evolution for the ultra-demanding innovative flange design of a PE 100 fitting which would durably join steel and PE 100. The extreme dynamic loads to which the flanged connection is exposed in underwater service were, above all, taken into account in development. Excellent communications and co-operation between Reinert-Ritz and the project planners achieved successful in-company installation and have generated an extremely high level of confidence for the longterm tightness and safety of the flanged connection.

(Authors: Dragisa Dubocanin, Paul Hutchings and Michael Ritz, Reinert-Ritz GmbH)

 

More News and Articles