SteelNews.com Article
ThyssenKrupp Steel Europe Supplies Steel for Hydroelectric Power
Jul. 26, 2010 ThyssenKrupp Steel Europe AG is supplying 17,000 tonnes of high-strength, quenched and tempered plate to the Ingula pumped storage scheme project of the South African power utility Eskom. The steel will be used to manufacture piping up to 5.1 meters in diameter for the scheme.
The Ingula power station is currently under construction and is scheduled to come on-line at the end of 2012. With the €16.6 billion investment, Eskom aims to respond more flexibly to peak loads on the electricity supply grid.
The power station features two reservoirs each with a capacity of 22 million cubic meters. They are situated around 6 kilometers apart, with a height difference of 470 meters. Between them is a powerhouse with four 333-megawatt turbines, which can be used both as generators to produce electricity and as pumps. The underground powerhouse is connected to the two reservoirs by underground waterways.
During times of peak electricity demand, water is released from the upper to the lower reservoir, driving turbines to generate electricity that can be fed into the grid. During off-peak periods, the water is pumped back up to the upper reservoir. The off-peak electricity it consumes is said to be cheaper than the on-peak electricity it produces. The scheme also allows the existing power plants to be operated at more constant levels and therefore at lower cost.
The steel plates supplied for Ingula are 32 to 60 millimeters thick. The material, known as NAXTRA M 700, has a strength of 700 megapascals. It can also withstand temperatures down to -40 degrees without becoming brittle. The company says the steel owes its properties in part to a heat treatment process in which the material is first heated to over 900 degrees, then cooled with water and tempered.
The Ingula pumped storage scheme’s conduit system consists of tunnels and shafts, some lined with concrete and others—in zones exposed to particularly high water pressure—with NAXTRA M 700. A high-strength steel lining is also needed to stabilize the shafts on a permanent basis. NAXTRA M 700 will be used to manufacture altogether 4.6 kilometers of penstocks.
ThyssenKrupp Steel Europe is also offering technical advice, in particular for the welding of high-strength steel plate. The company notes that because the heat-treated material is heated again during welding, close attention has to be paid to welding temperatures and cooling times to ensure the material maintains its good properties in the region of the weld.