Andritz Hydro and Dillinger work together on pumped-storage technology

by David Fleschen

The fixing by the UN Climate Conference of all-signatory targets for the containment of global warming has resulted in a rapid rise in the significance of the generation of electricity from renewable energy sources and, concomitantly, also of the need for energy-storage facilities. The most important and cost-efficient method of storing energy on a major scale - pumped-storage technology - thus also underwent a steep upward trend. ANDRITZ Hydro, based in Vienna and one of the world's leading suppliers of electromechanical equipment and services for hydropower plants also became a partner in great demand for especially challenging projects. For the development of sophisticated concepts in steel, large component dimensions and high individual item weights, this hydropower expert puts its faith in Dillinger, the world's technological leader in tailor-made heavy plates, domiciled in Dillingen, in the Saarland region of Germany. The power-generation projects of Kaunertal (Austria), Nant de Drance (Switzerland) and Abdelmoumen (Morocco) stand as examples of this highly fruitful cooperation between the two companies.

The strengths of pumped-storage plants (PSP) can be found in their rapid reaction to fluctuations in the supply of and demand for electricity. Their technology assures high availability, high capacity and high flexibility, and involves only low operating costs and risks. This, for the energy corporations, guarantees the necessary grid stability and black-start capability in case of a sudden power failure. ANDRITZ Hydro is one of the largest global suppliers of the market for hydroelectric power generation: world-market leader in the field of bulb turbines, technology leader in Pelton turbines and an acknowledged leader in the field of service and modernisation for enhancing the output of existing hydropower plants. Its portfolio includes the entire spectrum of electromechanical equipment, turbines, generators, hydroelectric engineering in steel, accessory equipment and services for hydropower plants of all types and sizes, ranging up to more than 800 MW output per turbine unit. Some 7,000 employees, at 25 global locations in Europe, Asia, and North and South America, demonstrate the company's proximity to its markets. Up to now, ANDRITZ Hydro has equipped more than 500 pumped-storage plants, with a total output of 40,000 MW.

As Vice President Penstocks & Gates, Helmut Friedl is responsible globally at ANDRITZ Hydro for the steel-engineering sector for hydropower plants, with a particular focus on penstocks, armouring, branched distribution pipes, grills, gates and the appurtenant equipment. He has also played a leading managerial role in the Kaunertal, Nant de Drance and Abdelmoumen projects.

The expansion of the existing generating plant at Kaunertal, in the Austrian Tyrol, marked the inception of even more intensive cooperation with Dillinger. At a height of 2,000 metres in a high alpine valley, generating capacity was to be increased by just on 1,000 MW, to a total of 1,370 MW, via the addition of an artificial storage lake as the upper reservoir, a second lower reservoir and a second power plant. This would convert the existing flow-through power plant to a pumped-storage configuration. Rockfalls on the surface of the slope additionally necessitated replacement of the existing penstock by a new duct located below the slip line. The design and installation of this duct was also to take prior account of the upcoming increase in the output of the power-generating plant.

ANDRITZ Hydro was commissioned for the construction of this penstock following an exceptionally complex short-listing procedure. The potential suppliers of this duct received from the client plates, which they then had to weld using specially developed processes in their welding shops on the basis of the weld-filler materials selected. An independent test institute evaluated the results for suitability for use in the rock using the sophisticated TOFD and phased-array inspection procedures. The verdict was incorporated here into an initial applicant evaluation. Subsequent forming of the plates into a pipe with a diameter of more than four metres, with various wall thicknesses, and welding of circumferential and longitudinal welds, were the definitive elements of evaluation in the next stage. In addition, the candidates also had to locate a steel supplier capable of demonstrating significantly higher toughness indices than specified in the relevant standard.

The customer permitted steels of Grade S620 as the maximum allowable yield strength. Special requirements concerning the size and thickness of the plates to be used also applied in the case of the bifurcations - the branching elements of the penstock, with a diameter of five metres. The search for a suitable supplier of the steel was by no means easy, in view of the relatively small quantity required (900 tonnes) and of the challenges associated with the validated requirements - optimised Charpy V-notch indices in the parent material and in the weld, and the required cost-efficiency, with on-time production and minimal failure rates. ANDRITZ Hydro located the sought for partner in Dillinger and was commissioned for supply, design, fabrication and installation of the penstock for the Kaunertal power-generating plant. "Dillinger is the absolute expert when it comes to high wall thicknesses", notes Helmut Friedl on his selection at the time. He adds: "In addition, Dillinger also had a larger hardening quench than other producers and was thus able to supply these demanding plates not only in the required thickness but also in correspondingly large lengths and widths." After extremely intensive discussions between the client, ANDRITZ Hydro, the operator, Tiroler Wasserkraftwerke (TIWAG) and Dillinger, the steel concept elaborated by Dillinger was approved.

On this basis, the steelmaker then produced at the Kaunertal generating plant, specially for the bifurcations, high-strength DILLIMAX S620 QL proprietary steel in thicknesses of 90 to 120 millimetres. "One of the greatest challenges in building pumped-storage hydropower plants with pipe diameters of five metres or more is the particular grade of steel used", remarks Helmut Friedl on the importance of the corresponding capabilities on the part of the steel producer. Wall thickness will also increase in parallel to diameter. Cost-effective production of the hydropower-plant components is made possible only by high-strength steels with good weldability that also permit fabrication using thinner wall thicknesses and thus allow shorter fabrication and installation times. The carbon equivalent (CEV/ECC) assists in achieving higher mechanical strengths. Good steel weldability necessitates the lowest possible carbon equivalent, however. "Dillinger was willing and able to develop for Kaunertal a solution with a CEV below the standard rating which nonetheless met the requirements for maximum allowable yield strength and dimensions", enthuses Friedl.

Another special feature of the Kaunertal project was a small fabrication shop which ANDRITZ Hydro created, due to the restricted transport possibilities, at the top of the mountain. Here, the plant engineer welded together the six-metre pipes fabricated down in the valley to make the required twelve-metre-long segments of differing diameters. These were then transported and lowered into the rock. Another definitive reason for ANDRITZ Hydro winning the project became apparent in installation in the tunnel: the hot-wire TIG welding system used by the plant engineer for the entire sloping tunnel at Kaunertal. The preheated uncoated solid wire used by the automated welding unit minimises the hydrogen content in the deposited metal and thus the risk of cracking. All the branch elements for the penstock were also delivered in single pieces up the mountain. There they were welded together into formats that could then be transported into the tunnel and assembled. The new penstock for this hydropower plant at Kaunertal was commissioned in 2016. Commissioning of the upper reservoir is anticipated in 2032.

Source and Photo: Andritz Hydro

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