Abstract
Today, the average worldwide efficiency of coal-fired power plants stands at about 33 percent. The consistent use of state of the art technologies would enable an increase of the average efficiency of up to 47 percent and thus a sharp reduction of greenhouse gas emissions. The importance of improvements in this field becomes apparent when reviewing e.g. plans in Europe in 2017 for new power plants to be built across the continent. About 44 percent of the envisaged 153 gigawatts are still to be generated by fossil-fuel power plants [1]. One technical solution is to increase the steam turbine inlet temperature to 700°C. This, however, requires the use of nickel-based superalloys. Only these alloys satisfy all the requirements with regard to high-temperature, corrosion and oxidation resistance and creep behavior [2], [3]. Due to their relatively poor machinability, forgeability and high material costs compared to the steel-based alloys they are to replace, a more effective welding technology is needed to overcome the disadvantages of conventional welding technologies, i.e. large quantities of filler metal required and high energy input per unit length resulting in distortion and the potential reduction of high-temperature properties.
Highlights
Introduction and motivationAs a consequence, a multi-pass welding technology needs to be developed to overcome these limitations and to ensure the economic, innovative and low-damage production of components such as reheaters, pipes and valves for example by using Alloy 617B/occ [11]
The objective of the given research and development results was to develop the Laser-MPNG welding technology to join pipe perspectival elements made of Alloy 617occ
The welding head enables the possibility to use LaserMPNG to produce weld seams that meet the quality requirements according to international standards
Summary
A multi-pass welding technology needs to be developed to overcome these limitations and to ensure the economic, innovative and low-damage production of components such as reheaters, pipes and valves for example by using Alloy 617B/occ [11]. The approach is to develop what we call the laser multipass narrow-gap (Laser-MPNG) welding technology. This paper will present the advantages of the new technology, the developed welding equipment and the results of welding tests in the lab as well as first results of low cycle fatigue properties at 700°C
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